CH stretching frequencies, bond lengths and strengths in halogenated ethylenes

Spectrochimica Aeta, Vol. 31A, pp. 1167 to 1186. PergamonPreen1975. Printed in NorthernIreland

CH stretching fkequencies, bond lengths and strengths in halogenated ethylenes D.

C. McICE~LN

Department of Chemistry, University of Aberdeen, Aberdeen AB9 2UE,

Scotland

(Received 11 September 1974)

Ab&ac&New i.r. studies have been made of the CH stretching and other relevant bands for CH,=CHF, CH,==CHCl, CHD==CHCl (cis/tram) CHD=CDCl (ci-a/trana), CH,==Cmr, CHD==CHBr (cis/tnzns), CHD=CDBr (cia/tmna), CH,==CF,, CHCl=CHCl (cia and trams), in gaseous and/or condensed phases. CHBz==CHBr (ck/travw), CHCl=CCl, and CBBr=CBr,, Some Raman spectra have also been recorded for CH,=CHF, CHCl==CHCI and CHBtiHBr. From these and previous data on CH,=CX,, CHX=CHX and CHX=CX, compounds, isolated CH stretching frequencies are obtained, from which bond lengths, dissociation energies and force constants are predicted. The substituent effects (S values) of CX bonds on the frequencies of CH bonds in cia, tram or dopositions are obtained either directly from the CH,==CHX isolated frequencies (X = Cl, Br) or indirectly from those of the X, and X, species (X = F, Cl, Br). The fair agreement between the two sets for Cl, Br shows that the effects are approximately additive; the incomplete results for the fluorides are promising in this respect. A pronounced tram effect of the CX bond (S: > Sp’ > StBr > St’) is discovered, comparable with similar effects in haloalkanes. S,’ and 8,’ are muoh higher in the ethylenes than in alkanes. An unusual apparent case of Fermi resonance is discovered in vinyl bromide. One component of a dyad is almost unobservable in both i.r. and Raman spectra.

INTRODUCTION

EXPERIMENTAL

In the preceding paper [l] isolated CH stretching frequencies

were

obtained

for

the

olefinic

In&red

CH

spectra

were recorded

Elmer 226 spectrometer.

on a Perkin-

Frequencies are accurate

bonds in propene and isobutene, and the effects of

to about 0.5 cm-l except where otherwise indicated.

methyl

A few Raman spectra were recorded, the gases on

substitution

discovered.

on

o(, trans

and

cis bonds

In the present work the substitution

the

University

of

Glasgow

Spex

Ramalog

effects of halogen are studied in a variety of halo-

instrument,

genated

with external recorder for scale expansion.

ethylenes

with the object

of comparing

the liquids

on a Cary

4

83 equipped Neon

these with the a, trans and gauche effeots of halogen

calibration

lines were used in each case, and the

in

calibration

error was

alkanes

[2, 31.

studies include

Previous

partial

deuteration

workers on 1,l -dibromoethylene,

[S], also on vinyl chloride, of EDQEL~ and ULTEE 1,l dichloro

ethylene

[9], of SHI~OUCHI

ethylene [lo], of B=

on vinyl fluoride [ll]

and OVEREND

ethylenes

these, only the last was conducted

1121.

Of

with resolving

power adequate for the present purposes.

to the usual Fermi resonances, the CH stretching often

The earlier controversy

weak

or unobservable.

over CH,=CF,

instance arises from this cause.

In the vapour

phase, two bands attributed

v1 and 2v, of almost equal intensity 3079

and

3116 cm-l

frequencies

were

BERNSTEIN

[14].

apparently

also

Rough

The spectra in the 3 ,um region of halogenated ethylenes are difficult to interpret, since in addition are

CHBr;CBr,

on

and CHRISTENSEN

and of CMO

on cis and trana 1,2 difluoro

fundamentals

or better.

RESULTS FOR INDIVIDUAL COMPOUNDS

[4] vinyl bromide

[6] and chloride [6, 71, of ENOMOTO and ASAEINA on l,l-difluoro

&l cm-l

those of DE HEMPTINNE and co-

estimates

are 3094

f

close

respectively: to

those

vg near affected

to

were seen at the

liquid

of Eves

and

1663 cm+

(gas)

Fermi

resonance.

by

is

of vcH based on i.r. intensities

6 (gas) and 3074 f

5 (liquid).

CHCl=CCl,

[9, 131 for

A type A band was observed cm-l

1167

at 2996.6

f

0.1

and a further weak broad band at 3166 cm-1

1168

D. C. MCKEAN

presumably affected

due

to

by 8 Fermi

intensity liquid,

2~s.

vz is again

resonance,

apparently

being seen at 1561 and 1590 cm-l. vi lies at 3082 cm-l

2vs is apparently of ALLEN 3000 f

according [16].

In the

to [15], and

absent from the Raman

and BERNSTEIN

both

two bands of equal

estimated It

vCH is taken to be

cis (-3 mode

MANN et al. [ 171 record dyad

in the gas a close Fermi

3170 and

3120 cm-l,

ponent of which is the combination The maximum likely

3150 *

one

tram

com-

is 25 cm-r,

20 cm-i.

Thus

CHI==CHI

being

dubious appear

quality

for

[18, 191.

to be about

and the tram

these

The

cis

are

shift, v:S, is 3050 *

visible is

(vi),

V lrand

3070 (vs) and 3090 (vi),

Applying

a 20 cm-1

10 cm-l,

a$,,,

10 cm-l.

spectra

of

[20] studied

gaseous

(Table

and

liquid frequency 3059.7 cm-l Dowling

liquid

essentially

pure isomers.

represents

line,

the

polarized et al.

resonance

the b, mode, vs, and the

a1 fundamental Raman

line

* Another = 3082a,).

vi.

possibility

The

observed

ah 3085 cm-1 is probably with vr.*

This

There is

the 3061.8 cm-l

(582 + 2 x 1252 = 3086, al) activated Fermi

cisltrana

1) confirms the earlier result.

no doubt that in the cis compound

additional

frequencies

are respectively

now

negative,

vcIIz*

measured

2 and

to explain

13 cm-’

tram interaction

the

opposite

There

here

in both constant

of that

is no Fermi

this reversal

are identical

The

data

in the

resonance

of sign.

vf:$ and

at 3089 4 1 cm-l.

of CRAIG and

OVEREND

[12] for the

suggest a Fermi resonance

Resonances

The agreement

the i.r. and

while DOWLING et al. [21] were apparently

able to investigate work

one.

between

the type A i.r. bands at 3136 and 3051 cm-‘,

EVANS and BERNSTEIN mixtures,

since the symmetric

in the gas.

the sign of the

cis-CHFdHF

CHBr=CHBr Raman

the

constant

CHF=CHF

gas-solution

3100 f

than

2. The cis and tram CH-CH

trans CHBr=CHBr.

of

frequencies

3023 (vs) and 3034 cm-l

ones about

all in solution.

compounds

the

trans CH-CH cm-l)

antisymmetric

gas and liquid

are shown in Table couplings

data

by

vi

(3129) the

CHF=CHF

coupling

(3130)

indicates

a very

frequencies

of about

8 cm-i.

is negative

1 cm-1 (tram)

of

and

cissmall

In the trans compound,

vCHis values

i.r. CHF=CDF

by 8 weak

gas

(0,).

frequencies

of

3110 for CHF=CDF

constant

compound. 3110 f

again 2 cm-l.

i.r.

and

interaction

the Raman

cis-CHF==CHF

of about

however, larger

between

liquid

coupling

with 2vz in x

for

CHF=CDF

v4 + 2vs

is va + Zv,, (1686 + 2

is

in

3080 & 1 and 3102 & 2 for the cis and

phases, only

positive,

the

species respectively

The

the

vCH =

5 cm-r.

The

the (~8

be

ri

3065 cm-l

the sign of the interaction

above

to of

CHCl=CHCl

1362 + 1788 =

shift possible

is about

one

about

greater

appear

position

seen that

cases being lies

becomes

resonance

at

rather

cm-l),

in both

unperturbed

is then is

compounds

trans

therefore coupling

5 cm-r in the gas.

3150.

and The

liquid.

spectrum

CHF=CF,

most

cis

negligible.

of

3114

for

indicate

The

a

sign of the

as in the dichloro 3123 f

are taken

1 (cis)

directly

from

and the

gas frequencies.

CH,=CBr, DE

748

HEMPTINNE

spectra

of

liquid

et

al.

[4]

CH,=CBr,,

measured CHD=C’Br,

Raman and

Table 1. CH stretching frequencies in CHBr=CHBr Assignment

Ci8

This work i.r. gas

i.r. liq.

3078.84 *

3161.5 3061.8

2Vd%l

v&b,) vl(al)

R liq.

3059.7

i.r. gas

i.r. liq.

R liq.

i.r. liq.

R liq.

3161 3064

3158

3162

3157

3081

v4 + 2V,(%) v&,) tmn.9 2v,(a,) vp(U V‘(%) VZ(%) * & 0.2cm-‘. 7 mdyn/A.

1584.0 3097.6B

3081.4

DOWLING [Z I]

EVANS [20]

1586

3089

3099

3081

3061

3959 f’ =

3084 1681

3085 I583

1586

+@ooQ

3156

3156

3089

3689 f’ = +0913-t

1681

1581

1169

CH stretching frequencies, bond lengths and strengths in halogenated ethylenes Table 2. CH stretching frequencies in CHCI==CHCI* Assignment

i.r. gas

i.r. liq.

R gas

R liq.

3167 3079.1

3177 bd

3167

3083*0t A

3090 ep 1693

3081.0 I 1587;

3163 vbd

3150

3083 sp

3072.8

1586 bd

1676f

CL4

1687.2 Wan.9

2v,(a,) r,(b,) VI(%)

3086.1

3095.6t B/A

va(ay)

f’ = +o.oosg

f’ = -0.021$

* This work. t *to*2 cm-l. $ Herzberg Infrared and RanaanSpectra of Polyatomic Molecules. Van Nostrand, New York (1946).

CD,=CBr,.

Although

3023 cm-l

in the H,

predicted at 2972 cm-l,

a resonance between v1 at

the spectra in the CH

species and

nearly

v,+o

+ 8oIIe,

might have been expected,

there is no evidence in the spectra to suggest that it occurs. 3108)

vCHav from the H, and

= 3065 cm-l,

agreement cm-r).

van from

with

Adding

3078

species is $(3023

this

17 cm-l

is

in

the HD for

+

reasonable

species (3061

a liquid-gas

shift,

crystal,

however,

A careful recent i.r. study of this molecule has been

by

made

~29

WINTHER

is not observed

can be located bands,

through

which resonance

since the latter’s the extent

No

Raman

value

vc_o

+ 6,,

calculated

value

in the intensities

since absolutely intensity

they is

[22].

and overtone 3133.7 cm-l.

as though

of the shift can hardly

The similarity dental,

the

looks

with

HUMMEL

in the gas phase but

combination

predict

vFHl at 3045-S cm-l Fermi

and

directly

it

were

in

at 2999.8, but is 3012.1 cm-l, exceed

5 cm-l.

may easily be acciare both very

found

weak.

attributable

to

vC=C + dona. voHaV is taken to be 4(3133*7 + 30403) = 3087 cm-l, which is in good agreement with the value of 3082 for vCH in CHD=&Cl, in CCI, solution. CHD=CCl,

Since no details

are available,

the

[lo],

of the work

value

on

of 3087 for

voHis is preferred. CH,=CF, Due

to confusion

in the literature

over

assign-

ments for this molecule,

this has been investigated

here

Infrared

more

frequencies 6

completely.

are given in Table

gas and

3, and Fig.

crystal 1 shows

region.*

IO-cm

bands

at 3170 and 3049 cm-l

parison

with

(The former high

two relatively

weaker

ones

is actually

frequency

With

gas cell, the

to a very

stand out by com-

a doublet,

weak

and

[13].

vc_o

in

resonance

The

alternatively

assigned

6,,

below.

the latter the

with

mode

to the type

has a gas

is

vs + via,

in the earlier Raman

SMITH et al.

In the

strong and narrow

between

shoulder.)

which is conspicuous CHs=CCI,

in the

bands in the gas are very weak, absolutely.

subject

& 5 is adopted for vCHI’a.

stretching

60 cm pressure

work of

vs has been

A band in the

gas near 1412 cm-l

by SMITH et al. [13] and to the

sharp weak Raman

line at 1358.5 by EDQELL and

DLTEE [9].

With

improved

resolution

the weak i.r.

band near 1360 cm-l is seen in Fig. 2 to be de6nitely of type

B, although

the q-like features

and 1358.7 are more pronounced other three

type

prominent

1400 cm-l, Since

B bands

only

at two

at 1365.2

than they

There

branches

seen

&

1430.6,

to

1412.4

be

and

frequencies

+ 610 = 1412 (a,), 2 x 437

+ 650 = 1424 (a,)-the from the aI fundamental

third & branch must arise vs.

However,

all three

upper state levels are likely to be in resonance other.

The

type

are near

1393.0 cm-l.

a1 or b, combination

are possible here-802

each

are in

in the spectrum.

B band

at

with

1362 cm-l

is

readily assigned as 437 + 925 = 1362 (b,) although * The i.r. spectrum was identical, apart from effects due to improved resolution, with that of SMITH et aZ. [13]. A weak narrow & branch at 749.1 cm-1 previously assigned as part of a type B difference band 13OI-660 is more likely to be due to a trace of CHF=CF, impurity. The torsional mode vg(at) was observed as a very weak band at 692 cm-’ in the gas phase, and aa a weak peak at 599 cm-l in the crystal, close to the weak doublet 606, 603 cm-’ due to vlp(b._,).

1170

D. C. MCXEAN Table 3. Frequencies of some vibration bands in CH,=CF,

Infrared (this work)

Assignment

Gas *

v,W V&l) iv5 + 2V,(%))

VI +

vs +

VIZ +

%(W

2vo + 2V&l) va + vs + vu(b) va + ~11 -t vd4

1

v4 +

~4 + *5 +

4594 BP w 4613 B, m 4390 ? w 4122 A, m 4000 B, w 3876 q, VW 3846 q, vw 3466 A, m 3174 B? w 3166.5 q, w 3164.0 q, w 3111.2 q, m 3101.2 q, m 3098.4 q, m 3092.2 q, m 3086.4 q, m

3014 q, vw 2946 q, vw 2932 q, vw 2831 q, w 1740.6 q 1727.6 q 1vs

%W

va:vo+ Vl&l)

vQ:vll

Crystal film?

3067.3 A, vs

Vl(%)

+

vl8:2vlo +

vdbl) vu(br)

v,(h)

VW

(ad

1430.6 1412.4 1 1393.0 1366.2 1368.7

Raman

q, w A, w q, w q B w q1 ’

1319 B, sh 13003 B, vs

Gas [13]

Liquid [Q]

4609 w 4108 w 3986 VW

~3440 bd, w 3169.5 31665 I’ 3109 bd, m

3171 VW, p

3112.2 w 3099.8 m

3101 VW, p

3094 bd, m 3069 bd, w

3086.4 w

3060 sh 3047.0 s

3068.3 ap, s

~1726 1442 ww 1432 vw 1391 bd, as, w 1362.6 sp, w 1366 bd, w 1320 1317 bd, w 1289 sp, s 1263 as, vs

1740.6 sp 1728.6 sp Is*pol

1728 vs. pol 1718 w. pol

1406 w

1389 VW

1368.7 vw

1369 m, pal?

1280 w 1212 vw

vdh)

964.3 B, s

v&4

926.6 821.9 809.3 806.0 803.6 802.1 797.3 796.4 796.2

vn@J

and hot bands

A, vs q, w q, m q, ah sh C, vs q, vw q, m q, w

949 944 m 914 bd, as, s

926.3 sp, vs

916 vs. pol

831 sp, s 816 bd, s

799 vw

810 m, dp

949 w, dp

714 vw

vuU4 Vo(%)

609.6 C, w

Vd%)

592 q, vvvw 649.7 A, m

eo(bd

437.0 B, vw

sp, w 699.6’sp, w 650 sh 648.6 s 439 sp, w

615 VW

603 8, dp

690 vw 649 m, pol? 440 vw

439 m, dp

* Pressures for bands 6000-2800, 690 cm-l, approx. 66 cm: for other bands, 8-100 mm, all in lo-cm cell. t At about 66 K.

1171

CH stretching frequencies, bond lengths and strengths in halogenated ethylenes CH,=CF,

cyst.film-651

gas-56

I

I

I

3200

I

1

3100

cm

I

I

3ootl

2900

CM-’ Fig. 1. Infrared spectm of C%&=CF,, 3200-2900 cm-r. Path length in ges, 68 cm Hg in IO-cm cell. Crystalline Elm at -66 K. there could be contribution to absorption here from

(type A)

802 + 550 = 1357

(b,) + 3174

CHF==CF,

as

well

from

us of

1412 of

rs,

to

can then be assigned as as + vT, 954.3 (b,) = 4128

(or).

ra8 and v, is then 3174 -

represent

the

us + rs is predicted

3136 cm-r, with complexity

approximate to lie near

of structure due to the

resonances on each component. prominent

as

at 1362 cm-l.

Taking position

(b,)

The spacing of the

Q branches at 31665

and 3154-O cm-l

compatible

The separation

3080 = 94 cm-l,

of

which is

with an HCH angle of about 122’ [23],

while van (Iv becomes

3127 cm-l,

agreement

rcH value

with

CHD=CF,

the

[Q],

particularly

which is in fair of 3133 cm-l

since

part

absorption between 3110 and 3085 cm-l

of

in the

may arise

fits well with the resonance on vs, and it is con-

from a level in weak resonance with v,. Although

cluded that va + vS has been displaced upwards by

the

about 23 cm-1 through a resommce with v1 below

additional peak near 3050 cm-i

Raman

spectrum

of

CHD=CF,

at 3057.3 cm-l.*

are no obvious combinetion

has

an

(Fig. 4 of [Q]) there

frequencies to account

near

for this, and the presence of an impurity seems as

3080 cm-l,

then the position of v,s”* (v,) can hardly

likely a source for it ES a Fermi resonance with r1

be

than

If

the lower

unperturbed about

position

of

vi

is

3080 + 80 = 3160 cm-l,

according to the correlation of DUNCAN [23]. previous

assignment

most improbable.

near

3100 cm--l

Tentatively,

[13]

Its

seems

the shallow mini-

mum at 3 174 cm-l is chosen for its centre, although the band may possibly be too weak to be seen. prominent

combination

band

at

A

4121.5 cm-l

* The Raman data leave no doubt about the aasignment of vl.

at

3127 cm-’

above.

chosen is 3130 f

The

final

value

of

van*’

5 cm-i.

The interpretation

of the crystal

hampered by uncertainty

spectrum

is

as to where v3 lies. If it

has moved as far down as the weak broad band st 1391 cm-l,

then the degree of resonance between

v2 -+- vs and r1 should increase (Ye also falls from gas to crystal).

The possibility then arises that the

crystal band near 3170 cm-l

is entirely due to the

1172

D. C. MCKEAN CH,=CF, cfyst.film-65K

Fig. 2. Infrared spectra of CH,==CF,, 1475-1350 cm-r. Path length in gas, 30 cm Hg in lo-cm cell. Crystalline film at ~66 K. vs + vs:vl

On

dyad.

increase in resonance more

than

istence

the

9 cm-l

of a doublet

indication

the

that

other

should

hand,

have

actually

found.

near 3170 cm-l

both

va8 and

such an

lowered

vi by

The

ex-

is perhaps

an

vs + vs are present

here.

state.

Observed

A feature vc=o

(a) on progressive

to bromide.

The labelled

species studied here were the cis and

trarr-_s mixtures compounds, chemical

of the CHD==CHX which

addition

of DX

CsD,

respectively.*

from

the Institute

the

University

contained

a

and CHD=CDX

are available The

from

to CsH,

small

and of HX

CHD=CHBr

de Physique

of

the photo-

The

amount

was a gift

Corpusculaire

Louvain. of

Vinyl

solutions.

CH,==CHCl

on the cold window which is thought ness

of

spectrum

most

of

chloride

initially

vapour

the

gas

bands.

results on annealing

By contrast in the unannealed

and and

isotopic deposits

in a metastable

to be crystalline

of

CHDtiHCl

Spectra were recorded in the CsHs. crystalline phases, the latter including solid

to

form,

from the sharp-

A

quite

(see Figs.

different 3 and 4).

bromide films the

bands were nearly all broad, as of an amorphous

deuteration,

(b) in passing

Forthe

CH,=CHX

to be about

is considered

has

which

2vs

represents

a

and the degree of resonance

to be zero.

CHs=CHBr

The band due to vc=o

two

are

to a very weak but close resonance

with

level

doublet

in

occurs

CHD==CHX

Q

1258 + 344 cm-l.

the

first

compounds but

these

branches,

in

which

the combination

branches,

chloride

species 2 x vs -

7 cm-l,

normal anharmonicity,

attributed

from

above increases in all these

vcH and 2v*o

is found

4-9.

is the fall in

As a result the risk of Fermi resonance

directions. Br

are listed inTables

to both halides

from gas to solid and (c) in passing between

CH,=CHCl,

frequencies

comon

overtone

vo=o

are

the

has

band.

cis and

Although

there is still no evidence for an abnormal where however

less precise.

the further

passing to CHD=CDX

the data are

fall in vG=o on

appears to produce 2ro=o,

about

perhaps in the crystal

phase of CHD=CHBr, However

by

Q

trans

30 cm-l,

except

fallen

In

has two

bands.

position of 2v-o,

v-o

now

again

A similar

resonance

involving

more especially

condensed

phase for the bromide.

a small in the

In the CH,=CHX species, a resonance between o=a and the combination level vcd + BFHa va below, near 2950 cm-l, has long been postulated

* Contrary to the &dings of ENOMOTOand ASAHINA [S], both cia and lrans CHD=CHCl resulted from the in the chloride, and in addition there is a very weak resonance between the almost exactly coincident addition of DC1 to C,H,.

CR stretching frequencies, bond lengths and strengths in halogenated ethylenes

I 33w

I 3200

I

I no0

I

I 3ooo

t

I 2soa

cd

Fig. 3. Infrared spectra in gas and crystalline film, 3300-2800 cm-l, of CH,=CHF, CH,=CHCl and CH,=CHBr. Gas pressures aa indicated, f?lm temperatures 78 K for Cl, Br, 66 K for F.

1173

__

1500

I~__

__L__I-I 1550

w

r 1500

cno=cocl

’

I 3200

I

I 3100

I

I 3000

Gas pressures in IO-cm cell-A, Fig. 4. Infrared spectra of CHD=CHCl and CHD=CDCI, 3200-2900 and 1625-1500~m-~. B, 11 cm; D, 12 cm with x 2 ordinate expansion. Crystalline films at 78 K.

___.._~

-I

C

w

I

I

C, 2 cm;

F-300

1176

CH stretching frequencies, bond lengths and strengths in halogeneted ethylenes Table 4. Some vibrational frequencies and assignments for CH,=CEIBr 8 i.r. (gas)* 31g8.2

i

32082 3202.2

K (gas)

ix. (cryst.)*t

t=l

3186 vw 3180 vw 3099 w 3090.6 sp, s 3077 sp, s 3002 sp, m

) 3112 3087 3027 2971

3112.3Q 11 3087GQ II 3026.5Q jj

sp, m sp, m sp, s vvw

2944 w 2934 vw 2838.6 sp, w 2687.6 1603.4 vs 1694 bd, vs 1673.6 sp, m 1667.6 sp, m I 1369 vs 1354 bd, s 1281 sp, w 1257 vs

2969.3Q (29778) 2966*2Q (2974.6) 28498Q (2860.9) 1604.1Q 1601.1Q

1601

1373.5

1373

1267.8

1258

Assignment

i.r. (8.8.) *t

2vc-0 vcdl

pa

+

2&I,

01

3072

vng

3006

VC= I 4

(2966.4) (2969.5)

VCLC +

&Ha

vc-a + &I* 1698.4

vc-c:v~ + vp

1691.6

(1268 + 344 = 1602)

iSC 1368

&Ii*

6H.7

l This work. t Annealed lilm at 78 K. $ Solid solution in CHD==CDBr at 78 K. 5 In brackets, frequencies calculated from fundamentals. I( *-to.1 cm-*.

Table 6. Some vibrational frequencies and assignments for CHD=C!HBr i.r. (gas)* 31378 (3148.6) 3134Q (3142.0) 3089.OtQ

i.r. (crystal)* 3134 bd, w 3122 w

i.r. (as.)*:

K (liq.)

PI

(3134.6) (3127.4)

2vc-a

tram,

3070.4tQ

3057.OtQ 2989Q 2945 2853Q vvw

1602.2 min 1574.3Q

3076 (3)

3066.6 w 3062 sh 1

3067 (3)

tram

2283 (7)

tram, vDl

2267 (10)

‘k vD#

ck VHs

1671 + 1295 2278.6 2276.6 I w 2262 sh 2266 m 1694 m

1696 (1) 1667.3 1666 (16)

15719Q

This work. t &to.1 cm-‘. $ Solid solution in CH,=CHBr

,‘a1

3037.6 w 3032 w I

1564 s

1294.7Q 12655Q 1230.3

vHIL

3074 s 3084.7 tQ I

3063 vw

Assignment

1663.7

1286 1265 1226 1188

bd, bd, bd, bd,

s s as, s m

l

at 78 K.

1290 1269 1228 1192

1543 1370 1304 1290 1263 1216 1186

1

(1) (1) (3) (2L) (7) (2) (10)

VC_C,

ci.9, tram

cia,VII tralta, vs tran9, vls

cw

v11

1176

D. C. MCKEAN Table 6. Some vibrational frequencies and assignments in CHD=CDBr

ix. (gas) *

i.r. (crystal)*

i.r. (5.8.) * t

R (liq.)

PI

Assignment

3129 bd, sh 3106Q

3056,3$Q, m 2937Q, vvw

2316elQ 2308.79 22799Q 22669Q 224&O&

1587.7Q w 15866Q w 16733Q w 1651~6Qvs 1649.6Q s 1544Q vs I

3107.5 w 3094 w 3082.5 w 3070 w 3062 w 3051 ms 3031 m 3022 vw 3005 vw 2788.5 w 2489.5 sp, s 2306.5 s 2297.7 8 2269.2 s 2256 bd, m 2245.6 vs 2231 bd, m 2211.6 sp, m 1614 w 1597 w 1573 8 1555 s 1538 vs

2vc_o and other combs.

(3085.0) (3078.4)

Ci8.

3044 (3)

Val

tram,

vne

2309 (3) 2291 (7) 2283 (5)

tram,

2241 (1) 2234 (5) I

Cis,VDaand

‘%

VDt VDQ

tram, vD1 1266 + 980

1614 (2)

1573 (6) 1566 (6) 1641 (15)

1542.5 1539.2

VC_C

Ci8,

tWZn8

1619 (1) This work. t Solid solution in CH,=CHBr r kO.1 cm-r. l

at 78 K.

Table 7. Some vibrational frequencies and assignments in CH,=CHCI

R (gas) WI

i.r. (m&a)*

i.r. (arm)*

3214*5Q (3221.8) 3120.6tQ 3086.4tQ

3214 ep, vw 3121 sp, m 3086 sp, s

3200 sp, m 3107.5 m 3080.6 sp, m

3197 sp, m 3106 sp, m 3077.5 sp, 8 3066.5 vw

3034.3tQ 3028

3033 3027I sp’ ’

3023 w

3021 bd, w

2950 sp, ms

2947 SD, m

i.r. (gas)

l

2961.2tQ(2981.2) 16128q 16109Q

1370.3Q

1280Q

1607 sp, vs

1603 bd, s 1582.0 sp, m 1578 bd, w 1634 bd, m 1396 bd, m 1387 sp, w

1368 sp, s

1279 sp, 8

1366.6 s 1362.3 sp, w 1284 bd, m 1279.8 sp, m

i.r. (9.8. m&a)+

ix. (8.8. arm)+

(3207.4)

(3204.1)

2vc,c VC% a*

I

(2968.4)

(2965.9)

1603.7

1602.2

% CEt

V8

1607 + 1030 + 394 vc,c + &a, W-c W

1581.1 sp, vw 1671 bd, m 1538 bd, m

1369.7 1359.2 sp* ms

Assignment

1364.7

1363.7

&H2

‘SC 1280 m 1273.7 vs

1280

*a3

This work. t -10.1 cm-l. meta = metsstable solid, arm = annealed solid, 8.8. meta = solid solution in metastablec HD=CHCl, = annealed solid solution, all at 78 K. l

as. arm

1177

CH stretching frequencies, bond lengths and strengths in halogenated ethylenes Table 8. Some vibrational frequencies and assignments for CHD=CHCl i.r. (gas)?

ix. (mete)?

3086.9 *Q 3082.4 ‘Q 30716*Q

3181.5 w 3148 bd, w 3140.5 w 3107.5 w 3080.2 s 3075.7 m 3062.0 m 30577 m 2873.5 w 2292 w 2276.5 vs

23045Q, vw 2262 min 1610 sh 15795Q,sh“S 1578.7

i.r. (s.s. meta)?:

3148 bd, vw 3139 bd, vw 3107 bd, w 3076.6 3072.3 3059.5 3057.6

(3152.2) (3147.0)

i.r. (s.s. ann.)t$

R (liq.) [6]

Assignment

3144 (05)

2%-c

3126 3080 3072 3062

tram, vgg

(0.5) (1) (7) (10)

cis, vsg c& VEg trans, vs 1

1576.1 vw 1573.5 sp, w

1573 bd, as

1302 E

1304.4

1303.3

1274 s 1271 sh

1267 s

1274.3

1270

1270 (3)

Wan-s, vs

1242 s

1243 s 1239 sh

1242.5

1241.8

1241 (2)

trans, vIp

1202 (5)

cis, vrp

-1578

vs

1377.0 sp, w 1349 bd, w

I 1242.5 min

i.r. (arm.)?

~1578 vs 1363.7 sp, m 1347 bd, w

1207 sh 1204 w I &O.l cm-l. t This work. $ Solid solution in CH,=CHCl

cis, VQ

*

at 78 K.

Table 9. Some vibrational frequencies and assignments for CHD=CDCl i.r. (gas)?

(31266) (3123.4)

i.r. (meta)t

i.r. (ann.)t

3140 sp, w

3138 vw

i.r. (8.8. meta)tz

3105 bd, m

3101 w

3095 m

3093 w

(3103.4)

3061.6 m 3063.9 m 2798 sp, w 2490 sp, w

3057.4 ah 30663 ms 2793 sp, w 2492 sp, w

23183Q 2314*5Q I

2309.4 m

2307.6

2290.2Q 2274.2Q

2279.7 8 2262.2 1118

2276.9 2264.0 1584.2 sp, VW 1555.6 1556.6 15526 bd, vs 1661.7 15505

3070.7 *Q

1663&J, s 1661.7Q, vs 16425Q, w 12699Q

1250

12505Q

1254

1268.5 1255.0 1247.2

ho.1 cm-l. t This work. $ Solid solution in CH,==C!HCl at 78 K. l

R (liq.)

P-31

Assignment

3130 (0.5) (3111.2)

3122’o

i.r. (8.8. ann)tS

(3107.8) (3101.4)

3108 (05)

%J-0

3081 (0.5)

I2309

1252.0 1247.7

tra%?, vDs

(8)

c’i8

2284 (0.5 2265 (2)

1563.9 1550.7 12675 12506

1657 (10)

trans,

cis,

vDIl

vDl

“Da

vc43

I

1264 (1)

tran.9,

v3

1249 (4)

cti,

v,

D. C. MCKEAN

1178 levels of vfHa and the combination 394 cm-l What

which

splits the band

is most surprising

similarity chloride

throughout

their

and the bromide,

is no

trace

of

spectra

with

about

almost (Two

4 atm.

in a l-m a very

frequency

Q branches

were

above-mentioned monicity

in the

ST”a) were almost

latter

In the crystal is of

compounds, concluded 10 cm-l that of

spectra,

the

the

from -

the

(vc=o

in fact, then

intensity

to

shift

in the

+

a

pairs,

may

stronger

clearly indicates

the

band,

(vHJ

and

for

frequency

moments suffice

to

spectra.

from

the chloride

cause

this

strange

The crystal

resonance

may

to the bromide

spectra

not involve

difference

would in their

also suggest that the $“a

so much as vcH

near 3075 cm-l. In a,,

the

10 cm-r the

eminently

and

modes are generally

is no evidence with

to

be the most reliable

CHD=CDX

below

suggest

vCH. The former

branch

apart.

significant

latter

resonances

and CHD==CHBr,

to

The

chloride

has

10 cm-l in

9228.3 cm-l. the

peaks

at

(v,,),

for

the

expected these

from

two

for the second

v, and

the

In

CHD=CHCl

frequency and

gas

zi

weak

spectrum

3071.8

are

both

because it is

peak, and the

of type A character, vHI, but not from

to the

very

Q branch

from

+

sum is then

than the highest

frequencies

eeems

of vcpc

in addition

because its pronounced

high proportion

resonance

which

assigned to the cia species, the former latter

sum

of the CH,=CHCl,

is deducted,

the

negligible,

crystal frequencies band,

3082.4 cm-l

The

a figure which

from the position

to allow

3062.0

(vH1).

is not

to the gas frequencies 3 cm-1

cia fre-

The identical

is deducted

reasonable

resonance

Figs. 4

Finally,

the

coupling

is

assumption

suggests

a

which is to be

vH1. Subtracting vi yields

frequencies

one

and the 4.5 cm-1 splitting

extra

Q

side, at 3071.8 cm-l, (there is also a very

of the tram

about

IO.0251 mdyn/A.

.

negligible, (b)

* GLASS and PULLEN [24], inter al&z, have drawn attention to this possibility, but this is the Grst instance of such an occurrence known to the author. It is even more remarkable in that no Raman intensity is seen in the gas, attributable to the combination band, in the bromide [26].

then become

value

the

larger.

is made The

negligible.

spaced about

two, at 3070.4 and 3057.0 cm-l, the

being more pronounced

cis coupling

the

vnlir =

3074.1 cm-r.

band near 3085 cm-l

with two Q branches

on the low frequency

and the bromide,

1300 cm-l and there

source of vCHi* values.

In both CHD=CHCl

4.5 cm-1

species,

species is then reckoned

and 5, the main CH stretching is of B/A type,

above

3075.7

term.

is

isolated

= 3062.2

2950 cm-l

lower by 4.5 cm-l

CHD==CHX

are

assume

three

from the CH,=CHCl

provided

an extra

transition

if the

involving

signs of the two

unperturbed

crystal

only by one cis coupling is obtained

spectra

frequencies

sum is then 9199.9 cm-l,

small change in

the

This

and the outer

we

the

3057.7 + 45

is in error,

of

of

If

tram form.

in the

moment

4) in

in the crystal.

pair

quencies

source

fundamental

to

inner

It is

or overtone

(Fig.

4.6 cm-l.

to the cis CHD=CHCl

v,.

and

about

from the CHX=CHX

to be zero, then

perturbed

lose this

A relatively

of

couplings

it is seen that

four appear

split

coupling

transition

magnitudes

the

that cis coupling is small compared

the

tram,

pair

property

transition

pair

both

of about

the

crystal,

each

Since the evidence

certain values of W, 6, and relative the

of

splitting

and of the tmns H,

now only the chloride,

in the gas, or to 3062 cm-l

6CHa.* Turning

moments.*

between

bonds

fre-

suggests that both vH1 and vH, lie close to 3070 cm-1

with

CH,=CHBr

that a combination state,

4.5 or 4.3 cm-1

in

and bromide

determining

ground

Considering

The anhar-

sharp

resonance

level having a small unperturbed from

two

the stretching

and H, ones.

two

is due to the little-known

namely

higher

from

difference

in the metsstable

an

3, the combination and

intensity

the

and H,

with

(20.0 for CH,=CHCI, Fig.

a Fermi

equations

intensities,

the

of the cis H,

ordinate

+ (a:=“)

strength

the negligible

represents

and

with

deriving

occurs in both chloride

gas spectrum

bond,

The

originate

band

on vc,o.)

much stronger, that

H,

attributed

similar

3063 cm-l).

cell,

18.3 for CHs==CHBr). band

the

at

plainly

instead of one other band in the g&4 at 3071.8 cm-r,

seen,

identical

lump

quencies

near

to that of the chloride.

(vo=o)

weak

More careful study, weak

resonance

differences

the

absence

As seen in Fig. 3,

a band

revealed

identical

between

is the apparent

2950 cm-r at normal pressures. expansion,

6 cm-l.

in view of the remarkable

of this resonance in the bromide. there

1607 + 1030 + by about

cis

that

represents

splitting,

This

coupling contingency

cir,

vH, and vns respectively,

If

the absolute

corresponding

the cis coupling

(a) vnl and vHs will approach

tram

the

CHD=CHCl

will

be

to

fls

is not

each other

proportionately

is considered

unlikely

however. * No decision is needed as to which fundamentals have been affected by this resonance.

1179

CH stretching frequencies, bond lengths and strengths in halogensted ethylenes

Fig. 6. Infrared spectra of CHD=CHBr and CHD=CDBr, 3200-2950, 1600-1626 cm-l. Gas pressures in IO-cm IO-cm cell-A, 14 cm; B, 1.6 cm; C, 18 cm; D, 2.3 cm. Crystalline 6lms at 78 K.

Examining

now the CHD&DCI

spectrum,

frequencies appear to be normal

Since the 2vc,o

in

the gas, Fig. 4, only a single rather weak type

A

in

band

is

attributed to the third band present, at 3140 cm-l,

is seen,

centred

at

3070.7 cm-l.

pltGnly due to vns in the tram

. .

proxmty

to

the

value

of

This

species*,

and its

with

gas.

However,

in the

metastable

anharmonicity

the aaaumption

deficit,

the

anomaly

that in one of the

is

species

there is a triad of levels in weak resonance.

vns in CHDaHCl

Any attempt to extract similar information from

suggests that there is little Fermi resonance here in the

their

solid,

the CD stretching

region runs into di&ulty

due

Fig. 4, three other bands appear at higher frequen-

to the coupling between CD and C=C

cies, two of which are clearly due to 2v+o,

which is known to occur in ethylene [26] and can

of the

lower pair of bands

3061.6 and 3063.9 cm-r, predicted,

ascribed

the first is exactly

and

vn,,

\

d

jHP

C==C

‘D,

also be seen in the cruder calculations of ENOMOTO and ASAEINA for vinyl quency

of -2309

cm-l

chloride itself [S].

A fre-

is clearly associated

with

vus, 88 the survey of DE HEBWTINNE et al. [6] shows,

I-I* \_/=s x/

D,

at

where

but the second is lower by 8 cm-l.

* The 1r(msspecies are respectively

and

to

stretching

and the i.r. gas data of the present work supports e cis/truns coupling ?a. -1

4 cm-l.

2275 cm-r cm-l H,

difference of slightly

The i.r. crystal in CHD=CHCl,

in CHD=CDCl and H,

stretching

frequencies

less than

of 2292 and

or of 2280 and 2262

however

bond

strengths

regions

and

do not reflect the

found from

clearly

the CH

variations

in

D. C. MCKEAN

1180

Table 10. Isolated CH stretching frequencies in vinyl chloride and bromide

H, \

c=c

X’

/Hz ‘H

1 CH,=CHBr

CH,=CHCI Gas

coupling

3062

3074.1

3058

Vi%

3071.8

3062

3060

3057.0

3035

Vz1

3082.4

3076

3072

3084.7

3070

the new feature

seen (Fig.

stretching

low

with

3035 cm-l,

frequency

Q branches

5. The apparent

shifts are noticeably for the chloride, compounds.

in

splitting

small.

Clearly

and

coupling The

band at 3056.3 cm-l that

3057.0 and

indicates

difference

sum z(

CH,=CHBr

the

deduction

of 10 cm-l

predicted

to

frequency

in CHD=CHBr

The from

be

the possibility having

suggests

spectrum

excellent

at 3070.4 cm-l.*

14 cm-l. a slight

of CHD=CDBr

B

strength,

must under-

no Raman

for

both

summarized

intensity

above

vinyl

in

the line

chloride

Table

10;

are considered

to be about

of

resolution

lack

band in one

of

by a Fermi Certainly

the

ostensibly

interaction.

The

in this region

work use.

available

adequate

in the 3 ,um region

and their

+3 cm-l.

Since

is

* A similar calculation using the crystal frequencies of CH,=CHBr and CHD==CHBr, assuming the bands at ~3074 and ~3054 cm-r to be the tram frequencies of the latter, puts the crystal value of vzl at 3031 cm-l, close to the doublet seen at 3035 cm-r.

only

and

together

on deuterated

vinyl

CH

the

fluorides

the normal

frequencies

poor

render

[l l]

species

in the present work, only a frequency

for the isolated

derives

3070.4

of a weak band at 3106 cm-l,

due to 2v*o, crystal

The

of little

the

A

since a type

[5].

are

calibration

to be

is in

been displaced

of about

a

vnr is

is then expected

to

nor

CHs=CHF

previous

that the 3056.3 cm-l

CHD===CHBr, shift

with

in this argument

corresponds

presence

are the

tram

which

be

the type

CHD=CDBr,

vcHis values

The

be

must 2vcEc,

involves

enough,

for liquid

at 3044 cm-l

lower

with the band observed

CHD=CDBr resonance

The

inevitably

Surprisingly

is reported

bromide

2vc,o

eztm to

and that

resonance,

3074.1 cm-l.

than

appear

seen at 3056.3 cm-l,

uncertainties

is prima facie

stretches,

for Fermi

uncertainty

A

these, and the frequency

= 3069.8 cm-l,

only

a type

in CHD==CHBr

From

agreement

of

in CHD=CDBr

3084.7 cm-l

almost

levels

band due to vH1, of unknown it.

and the

would

in the gas is necessarily

that the resonance

lie

to that found

observation

cis fundamentals.

3074.1-4.3

an

this is the Y=, frequency,

vt for

than

at 3050.5

It cannot be assumed that the band

fundamental

gas-crystal

of the two Q branches

3084.7 cm-l

chloride.

evidence

The

bands being

lines,

close to the 3055 and

resonance other

at 3106 cm-l

is surprisingly

strongest

are fairly

Fermi

participating.

annealing.

seven prominent two

bands of CHD=CHBr,

doublet

as was found in the CHX=CHX

tram-&

the

3035 crystal of

for the bromide

The separation

3089.0

identical

bigger

and 30305 cm-l, degree

that it must contain both

vHs components.

The

3055 and

may be due to inadequate

tram

complex, 5).

near

bands

The main crystal band at 3074 cm-l

at

at 3070.4

(gas phase) is obviously

broad even remembering cis and

surprisingly

are considerable.

bromide,

the crystal

Fig.

of the latter

Cryst.

3062

and 3057.0 in CHD=CHBr, connected

GE%3

3074.1

now to vinyl

of two weak

tryst .

VEl

to C=C

Turning

Mets solid

was sum

can be aimed

at

here.

At a pressure of 60 cm, the i.r. gas spectrum

(Fig.

3)

shows

3094 cm-l near

two

respectively

3000 cm-l.

The

strong

bands

with first

at

a third

two

bands

3140 and

weak

v~~~~and vEI modes, in large measure at least. Raman

spectrum

complicated, 3,002 cm-l

of the gas (Fig.

The

6) is rather more

but the high intensity leaves little

band

are clearly

of the band at

doubt that this is primarily

vg *. There is no sign of any i.r. absorption at this point in the gas phase, but in the crystal, a strong band is seen at 3047 cm-l which may be due of the 3000 cm-r

band

in the gas phase would then appear to derive

from

to v;=a.

The i.r. intensity

1181

CH stretching frequencies, bond lengths and strengths in halogenated ethylenes

CH,=CHF gas Raman

I

1

,

1

3150

3100

3050

3000

Fig. 6. Raman spectrum of CH,=CHF, a resonence

with

vHQ, if such a resonance

is to be

The only binary combination which its source. could give rise to it is the chief suspect in these molecules

namely

3935,

which

about

25 cm-r.

Raman

vo=o

would

a resonance

The extra

spectrum

shift

bands appearing

at 3074,3064,3037

ary

and various ternary

combinations, The

Table

11.

would

then

On the

some to

be

close the

the 3000 cm-l

band

resonance

arises from

While (2

to

vy”a

3062 cm-l. sum

which

is

In principle, the present

Table St

13 that

is

from the difference

The

a reinvestigation

species will reveal bond

of

directly

the

(2

obtained

ones

discussed

promising

to be worth

quoting

from

they

isolated indirectly

look

sufficiently

in Table

12.

of

“indirect”

deuterated

the

may

ones

A survey

CHBr=CBrs

is too

existing

evidence

tolerable

degree

A feature

that

only

C&H, greater, much cis,

one is possibly

(3060 cm-l),

while

less than most

are

12 shows

the value

for

appreciably

and a few, for the I?, and Fe compounds, greater.

A

closer

tras-wand

a effects

the differences

between

analysis

considers

the

to believe values

(Table

as

The

vonis in the cis, trans and a

results

of the CX bond, defined

low

by

* The other ternary combinations given in Table 11 are less likely in view of the gas-crystal frequency shifts they would produce.

that

largest

of

4 cm-l.*

and

change in halogen

the

amongst

one the S

predictions

therefore lengths

of

be reliable, etc.,

derived

12).

spectacular

Table

of the di-

This encourages

case also, bond

a

prediction

frequencies

prevails

the

The with

of the S values.

additivity

should

where

vCHis in

competible

ethylenes.

(Table

most

14B) or

The

value

about

of additivity

with

in

calculated

(Table

of Ta.ble 14C is the excellent

in this

therefrom

for S,

is to compare

14C).

the

S fair

An alterne-

those

S values

is therefore

vCHiJ for CH+ZHF together

error.

the situation

that

and tri-fluorinated

of the vCHis values of Table

shows

occur in part C for the bromide indicate

are

“indirect”

bromide

vCHfs with

of the absolute CH stretching DISCUSSION OF RESULTS

and

end

the “direct”

discrepancies

the individual below

values

is

results

for S, and S,, but a disagreement

vi = 9228),

partly

However,

frequencies.

the

&

S, - S,

14.

“direct”

tive way of representing

than the bromide

ones

of

chloride

for

the cis and

The

just at the limit of experimental

either

chloride

the

agreement

frequencies

or

in part A of Table

for

that

between

frequencies.

comparison

and

The combination

@HseCX,.

truns CHX=CHX

only

from the X,

VgHXdHX(cis),

tranr)

is obtained

it is quite clear that the fluoride higher

-

V&X=CHX(

-

from from

It is readily seen from

VijHX&H,

-

displayed

is feasible

or indirectly

VtfHXHx=cX,

observed

markedly

S, is

V!LHX&X,

values

6 cm-l.*

symbols

either directly

which

and bromide,

and X, isolated frequencies.

that

c&se its

and the value of

corresponding

those effects can be extracted

compounds,

the chloride

from

which

The

data in two ways,

the vinyl

below

the combination in

to the halogen,

ethylene.

S,, S, and S, will be used.

however

to exceed

then

in

relative

for

9290 cm-l.

vi = 9216)

only

3060

becomes

are in general

sum

of

frequency

It is possible

shift is unlikely

frequency

given

is 9271 cm-l,

1156 + 2 x 930 = 3016 cm-l, The

are

close to the value predicted

the F, and F, species.

between

or quatern-

position

interpretation

for the three fundamentals agreeably

which

unperturbed

appear

above

of

in the

and 3012 cm-l

may then be the result of small resonances vy”s at 3062 cm-l,

of

gas, 3150-3000 cm-l.

positions

+ SoHa, 1655 + 1380 =

imply

cd

chemical

14 is the

feature

decrease

from fluorine

( $40)

of the

in S,

with

to bromine

* This would entail the maximum possible Fermi resonance shift on Y 1 in this molecule (18 cm-l) _

1182

D. C. MOKEAN Table 11. Some vibrational bands of CH,=CHF

ix. (Gas.)*

R (Gas)*

3300 A, vw 3140.0t A/B, w

i.r. (Cryst.)*

i.r. (Gas) [ll]

3281 ma 3130 VW

3140.0 w 3107 ww

3096.0m 3093.5 B/A, w

Assigmnent$

3315 (3160)

2 x 1664.6 = 3209.2 vz**a= Y1

(3116)

VEa =

3107.5 8

I I

3091.7 m

1306 + 2 1380 930 x +862 863 = =3104 3098

(3080) 3074 bd, w 3062.1 as, s 3055.5 3053.6 I In 3037 vvw

1056 + 2 1666 930 x +711 483 = =3077 3068 V$B = vs

3047.5 8 3032 w

1665 + 932 + 483 = 3068 1306 1380 1156 1166 1666 1665 1666 1647

3011.5 VW 2999.5 sp, m 2961 vvw

A, vw 2949 vvw 2804.7 t A, VW 2999*8t

v,

2989 sp, ms 2763.0 w 2649 m 1658 sh 1647 bd, vs 1377.3 1370.4 1 sp, 8 1299 s;, 8 1138 1121 1 v*

1654.6 A, vs 1379.6 A, w 1304.5 A, w 1166 A, vs

862 C, vs

879

711 C. m

876 I “’ 716 sp, m 488 sp, vs

2810

+ + + + + + + +

2 x 802 = 3029 930 + 711 = 3021 2 x 932 = 3020 2 x 930 = 3016 1380 = 3036 1304 = 2969 1166 = 2811 911 = 2558

1664

V&C = V(

1380

6OH*

1306

&T* = ve

1156

VT

=

vs

930.2 0

Vl o@T

931.5 0

V8

863

v11(a1

711 483

%*(a 1

n

I

vgW)

* This work. t f0.1 cm-l. $ Only a’ ternary combinations listed. $ From R. EL~T and A. OSIUIM, J. Mol. Spectry 39,367 (1971). ( - 3). The only information

for iodine, on S, - S,,

leaves little doubt that this trend extends here also. This

is a trulzrr effect

those

found

displayed tudes

in alkyl

in Table

of ronis

compounds thus

to

values.

for which

15. The reversal

a

comparison

and

direct

consequence

the

of

alkanes

X=Cl,

alkanes

interest

are noted

of Br-Cl-F,

to a depression

of

is

this

S,

to fluorine.

appears

of S,

for the fall

in S,

which

to

the

series in CHsF

has

due to the trans

effect of the fluorine lone pairs [32]. chlorine

Br, I

between

is in the

been attributed ethylenes,

CHX=CHX

X=F

in the sequence

the

are

of the magni-

in the cis and trans be

and The

data

than

effect of the halogen.

tram

Another ethylenes

to, but greater

halides,

between

seen

changing

similar

rise

By contrast, slightly

in

from

Since at first sight this might

appear

to stem

from

it may be observed are

rather

108.5 f

of the alkane

results is the constancy

a

quite

chlorine

and bromine.

however

the general

substitution

is VCH *

Turning

agreement

S, might

be thought

with S, in the ethylenes,

shows

marked

increase

effect

bromine

is to raise

of bond

length,

to the predictions

discrepancy

[27-301 arising

over

of a, and cis or gauche

and

the present

predictions

from the graphs of [31] and the previous rs values

to

but here

In both types of compound

of chlorine

between

[29],

[33]).

of S, for all four halogens. fluorine

angle, /\ values of HCF

(110 -& lo, CH,==CHF,

CHsF,

be comparable

H-C-F

that the reported

similar

0.5’,

A feature

a differing

is

generally

fair,

the of rs

microwave the

largest

in the case of cis-CHFSHF.

CH stretching frequencies, bond lengths and strengths in halogenated ethylenes

1183

Table 12. Isolated CH stretching frequencies, bond lengths, dissociation energies, force constants

v&t

CHBr=CBr, CHCl==CCl, CHF=CF, CHI==CHI (Ci8) CHI=CHI (tr) CHBr=C!HBr (cis) CHBr==CHBr (tr) CHCl===CHCI(cti) CHCl==CHCl (tr) CHF=CHF (cis) CHF==CHF (tr) CH,=CBr, CH,=CCl, CH,==CF, CH,=CHBrll(Hi) (H,) (H,) CH,=CHCl I](II,)

3094 3100 3150 3060 3100 3080 3102 3089 3089 3123 3110 3078 3087 3130 3074 3057 3085 3074 3072 3082 3087 3100 3080

VW (%I CH,=CHF II8Wd (Hd (H,)

r,(obs.)t

r&red.)

(cm-r)

(A)

(5) (6) (5) (IO) (10) (1) (2) (1) (1) (1) (1) (5) (3) (6) (3) (3) (3) (3) (3) (3) (10) (10) (10)

1.082 1.081 1.077 1.086 1.081 l-083 1.081 1.082 I.082 1.079 l-080 1.083, 1.083 1.078, 1.084 1.086 1.083 I.084 1.084 1.083 I.083 1.081 I.083

(mdyn

6.244 6.264 5.436 6.096 6.264 6.196 5.270 6-227 5.227 6.342 6.298 5-189 6.220 6.366 6.176 6.119 5.213 6.176 6.169 5.203 6.220 5.264 6.196

112.0 112.5 116.8 108.2 112.5 110.8 112.7 1116 111.6 114.5 113.4 110.6 Ill.4 115.1 110.3 108~8 111-2 110.3 110.1 Ill.0 111.4 112.6 110-S

1.089 1301

1.079 l-086 1.087 1.079 1.090 l-078 1.079 l-087 1.077 1.082

fOH’ A-1)

Dies(pred.) (kcal mole-r)

(4

[30] [27] [27] [27] (6) [28] (6) [28] (6) [28] (3) [29] (3) [29] (4) [29]

* Diatomic approximation. t In brackets, errors in last figure. 8 Indirect estimates (see text). 11Numbering of atoms:

H,

HE \

/ C==C

X’

‘H

1

Table 13 H

H \

x’

c=c

ix

H \

‘x

X’

H \

ix C==C ‘H

c=c

x’

/”

\

‘x

c=c

H’

/” ‘X

Effects on v&

The large value previously

of

puzzled

1.089 A for r, in the latter LAWME

and PENCE [30] who

bromide, than

the CH

the

appreciated the shortening effect of a CF bond on

indicated.

the trans

dissociation

CH

one.*

In

the vinyl

chloride

and

bonds

microwave

are much results

There are apparently energies

to

more

have

similar

previously

no experimental

compare

with

those

predicted in Table 12. * Insofar as the major surprises in this work are the abnormal effects of fluorine on CH bond strength, it ia puzzling to find that an ab initio treatment of C&H, and C,H,F [34] describes the effect of fluorine substitution on the /I carbon and hydrogens as “negligible”.

SPECULATION The variation

in Y&S

halogen in the tram

with the nature of the position is plausibly explained

1184

D. C. MCKEAN Table 14. A. S values for halogenated ethylenes (cm-r) F Direct

8, S, 8, 8, - 8,

Br

Cl Indirect

Direct

Indirect

27 40 20 13:

14 12 22 -2

11 11 13 0*

Direct

I Indirect

14 -3 26 -17

Direct

Indirect

14 -8 16 -222

-509

B. Predictions of v& from direct S values F Species

Pred.

Obs.

CHX=CX, CHX=CHX(cia) CHX=CHX(trans) CH,=CX,

Br

Cl

3150 3123 3110 3130

I

Obs.

Pred.

Obs.

Pred.

Obs.

3100 3089 3089 3087

3108 3094 3096 3086

3094 3080 3102 3078

3096 3082 3099 3071

3060 3100

Pred.

C. Predictions of v& from indirect S values F

CHX=CX, CHX=CHX(cie) CHX=C!HX(trans) CH,=CX, CHs=CHX(H,) (H,) (H,)

Br

Cl

I

Obs.

Pred.

Obs.

Pred.

Obs.

Pred.

3150 3123 3110 3130

3147 3120 3107 3127 3087 3100 3080

3100 3089 3089 3087 3074 3072 3082

3095 3084 3084 3082 3071 3071 3073

3094 3080 3102 3078 3074 3057 3086

3082 3068 3090 3066 3072 3052 3076

Obs.

Pred.

3060 3100

Table 15. S values in some halo-alkanes* (cm-r)

Species CH,CH,X

Substituent effect

F

Cl

Br

I

++2: -17

+>E -28 +33

-14 $22 -35 +46

-22 +19 -41 +48

St S# S, -8, &

(CH,),CX

CH,X * Date from [2,3,31].

& S, 8, - 8,

$36 +24 +12

$12 +25 -13

+1 128 -27

-15 +25 -40

&

-16

+20

+35

t-37

t = trans, g = gauche.

CH stretching frequencies, bond lengths and strengths in halogenated ethylenes in

terms

electron

of

a

repulsion

pairs in the C-H

this repulsion increasing electron This

density

in

“valence-bond”

MO description electrons

of the

on N or 0,

the

bonding

and trans C-X

between

bonds,

as the halogen the

picture

sequence

relinquishes F-Cl-Br-I.

is equivalent

of the average frequency of 3060 cm-l, adopted here, may be necessary (J. i. DUNCAN, private communication). Treltda in S_, S, and 8, will be unaffected, but their additiwity gay-be poorer than is apparent here.

to the

tram effect of a lone pair of due to H~OW

1186

et al. [35],

REFERENCES

[I] D. C. MCKELLN,rSpectrochim. Acta, 31A, 861 (1975). which is attributed to partial participation of the [2] D. C. MCKEAN, S. BIEDERMANN and H. B~~RQER, Spectrochim. Acta 30A, 846 (1974). lone pair in a 0 * CH orbital directed to the bond in [3] D. C. MCKEAN, 0. SAUR, J. TRAVERT and J. C. question. It is tempting to associate these trans LAVALLEY, Spectrochim. Acta, to be published. effects, with the unusually high uHH coupling [4] M. DE HEMPTINNE, C. VELQHE and R. VAN RIET, constants between hydrogen atoms in the trans Bull. Class. Sci. Acad. Roy. Belg. 30, 40 (1944). [6] J. CHARETTEand M. DE HEMPTINNE, Bull. Clara. configuration, but it is not obvious that the two Sci. Acad. Roy. Belg. 38, 934 (1962). phenomena have the same theoretical basis [36]. [S] M. DE HEMPTINNE, G. GERMAIN-LEFEVRE, R. It seems more likely however that the h-an-9 VAN RIET and D. LENAERTS, Bull. Class. Sci. CH-CH stretching force constant owes its origin Roy. Belg. 46, 310 (1960). to the above effect. [7] M. DE HEMPTINNE, R. VAN RIET and A. DEFOSSEZ, Bull. Class. Sci. Acad. Roy. Belg. 47, 161 Since the trans effects of halogen previously (1961). found in halo-alkanes are more pronounced in [S] S. ENO~~OTOand M. ASAHINA, J. Mol. Spectry 19, ethylenes, and since the most potent of all tram 117 (1966). effects are found from unshared pairs of electrons, [9] W. F. EDQELL and C. J. ULTEE, J. Chem. Phys. 22, 1983 (1964). in oxygen and nitrogen compounds [32], it is [lOI T. SE~~ANOUCHI, l’ablee of Molecular Vibrational natural to consider whether the abnormal weakness Prequench Part 3. NSRDS-NRS 17 (1968). of the aldehydic CH bond may not arise in part [ll] B. BAK and D. CHRISTENSEN,Spectrochim. Acta. at least from a tram effect of the unshared pairs 12, 355 (1958). on the oxygen atom. The same effect in a molecule [12] N. C. CRAIO and J. O~EREND, J. Chem. Phys. 51, 1127 (1969). such as CH,=NMe would produce CH bonds [I31 _ _ D. C. SMITE, J. R. NIELSEN and H. H. CLAASSEN, in the methylene group differing considerably J. C&m. Phye. 18,326 (1960). in strength. However, the solid state i.r. spectra [141 J. C. EVANS and H. J. BERNSTEIN. Can. J. Chem. of HENZE and CURL [37] do not show a very much 33, 1171 (1955). larger separation of vas and ys than usual. A w1 M. DAVIES and G. J. BOOBYER, J. Chem. Sot. B. Phye. Org. 910 (1966). further consideration concerning the aldehydic [161 G. ALLEN and H. J. BERNSTEIN, Cum. J. Chem. frequency is that there are in fact two unsolved 32, 1044 (1964). problems: firstly, why the frequency is so low in [171 D. E. MANN. N. ACQUISTA and E. K. PLYLER. J. H&O (2813) and CHsCHO (~2773) and secondly, Ch&m. Phye..22, lS& (1964). why it rises again to about 2940cm-l in HCOOCH,. 1181 S. I. MILLER, A. WEBER and F. F. CLEVELAND, J. Chem. Phya. 23, 44 (1965). The latter, formally, represents an cc effect of R. H. KR~P, E. A. PIOTROWSKI,F. F. CLEVELAND OCH, of about 130 cm-l, which may be an El91 and S. I. MILLER, Dev. Appl. Specty 2, 52 exaggerated form of the a effect of fluorine in a (1962). ethylene. The usual interaction postulated between [201 J. C. EVANS and H. J. BERNSTEIN, Can. J. Chem. 33, 1171 (1966). oxygen or halogen and a double-bond involves the J. M. DO~LINQ, P. G. P~RANIP, A. G. MEISTER v electrons, and just why this should affect so r211 and S. I. MILLER, J. Chem. Phye. 28,233 (1957). profoundly a u CH bond remains a mystery. [221 F. WINTHER and D. 0. Hu~~~~,Spectrochim. Acta 23A, 1839 (1967). Acknowledgement-I am indebted to Dr. A. P. LANE and Acta 26A, 429 the Chemistry Department, University of Glasgow, for ~231J. L. DUNCAN, Spectrochim. (1970). the Raman spectra of the gaseous samples, and to Dr. D. VAN LERBERQHEfor the samples of CHD=CHBr. 1241W. K. GLASS and A. D. E. PULLEN, Tram. Faraday Sot. 59, 26 (1963). I thank the Science Research Council for the above Raman facility and also for a grant towards the pur- [251 C. W. GULLIKSON and J. R. NIELSEN, J. Mol. Spectry 1, 158 (1957). chase of isotopically labelled materials. I thank also Mr. B. W. LAWRIE for assistance in the preparation of [ZS] J. L. DUNCAN, D. C. MCKEAN and P. D. MALLINSON, J. Mol. Spectry 45, 221 (1973). the CHD=CDBr and CHD=CDCI. [27] D. DE KERCKHOVE VARENT, Ann. Sot. Sk. BTUX. Note added in proof: 84, 277 (19iO). Current studies of the CH stretching fundamentals [28] D. KIVELSON, E. B. WILSON and D. R. LIDE, J. Chem. Phys. 32, 205 (1960). of ethylene suggest that a small downwards revision 6

1186

D. C. MCKEAN

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[34] S. MEZA amd U. WAEGREN, Thor&. Chim. Acta 21, 323 (1971). [36] H. P. HAMLOW, 5. OKUDA end N. NAKAGAWA, Te&&xhm Lett. 2663 (1964). [36] M. KARPLUS,J. Chem. Phyu. 80, 11 (1969). [37] J. HENZE and R. F. CURL, J. Am. Chem. Sot. 86, 6068 (1964).