A partial vibrational reassignment of 1,3-butadiene

SpeotrochimicaActa, Vol. 31A, pp. 1201 to 1206. PergamonPress 1975. Printed in NorthernIreland

A partial vibrational reassignment of 1,3=butadiene Yu.

N. PANCHENKO

Molecular Spectroscopy Laboratory, Department of Chemistry, Moscow State University, Moscow 117234, U.S.S.R. (Received 16 August 1974) Abstract-An assignment of the experimental vibrational frequencies of 1,3-butadiene and its seven deuteroanalogues is given and the calculation of frequencies has been made. From the vibrational forms obtained the mean amplitudes of vibration and the Coriolis coupling constant The agreement of all these values with the experimental ones is quite &:as were calculated. satisfactory. I. INTRODUCTION

been investigated

Recently,

interest in the structure and spectra of

molecules

with conjugated

double bonds and, in

particular, in 1,3-butadiene

(Fig. 1) has risen once

again.

In

perform

view

of this,

a detailed

it appears

analysis

of

the

desirable

to

vibrational

spectra of as large a number as possible of the isotope-substituted

varieties of this molecule,

which

will permit a correct assignment of the frequencies of its vibrations. Hz \

7 /

G--H,

C3

//H-C, 1

\ H6

recently.

These data show that

some experimental frequencies must be reassigned. IL Ml3THOD OF CALCULATION A set of force constants for 1,3-butadiene has been determined from the frequencies of the C,H, and C,D, molecules by the interative consistency method using an algorithm given previously [22]. The data on the frequencies of the intermediate deuteroanalogs have not been utilized since they are connected with the frequencies of the C,H, and C,D, molecules by strict or approximate isotopic rules [23, 241. A set of force constants obtained is used to solve the direct vibrational problem for six intermediate deuteroanalogs of 1,3butadiene. These results and the experimental data are given in Table 1. The geometrical parameters of the C,H, molecule are taken from [25]. From the vibrational forms of the C,H, molecule the mean amplitudes of vibration are obtained by the CYVIN method [26] (Table 2 and Fig. l), and the Coriolis coupling constants {;i,ns and &,.,s are calculated by the MEAL and POLO method [27,28] (Table 3).

\

III. ASSIQNMRNT OF VIBRATIONAL FREQUENCIES

Fig. 1. Model of the C,H, molecule. The vibrational spectrum of the C,H, molecule has been investigated repeatedly. The Raman spectra [l-5] and the i.r. absorption spectra [5-91 have been obtained for all states of aggregation. The vibrational spectra of such isotopic varieties of the I,3-butadiene molecule as C,D, [lo], 1,3-butadiene-2-d [ll] (see also the note in [12]) and 1,3-butadiene-d,-l,l,2 [13] have also been studied. The experimental material mentioned [l-4, 6-8, 16-131 and the calculation of the vibrational frequencies [12, 141 have permitted a fairly well-based assignment for the majority of the observed frequencies of 1,3-butadiene and its deuteriumsubstituted derivatives. On the basis of the same experiment [l-4, 6-8, 16-121, calculations have also been made of the vibrational frequencies by other authors [15-171. The inverse vibrational problem has been solved previously using the experimental results for C,H, alone [18, 191. The vibrational spectra of 1,3-butadiened,-1,1,4,4 7

[20] and 1,3-butadiene-ds-2,3

1211 have

In the C,H,

molecule the out-of-plane

were only reassigned

vibrations

[20, 211. In the i.r. absorp-

tion spectrum four bands are active which possess the type-C

contour.

at 907.8 cm-l

The assignment of the bands

and 163 cm-l

The band at 5245

cm-l

is completely

(rrs) of the C,H,

obvious. molecule

shifts in the long-wave direction by approximately 20 cm-l

(Table 1) with the successive replacement

of each atom

of hydrogen

on the central carbon

atoms by an atom of deuterium, e.g. when passing from C,H,

to C,H,D

and from C,H,D

The fact that the 524.5 cm-l, cm-r

bands

different

belong

to

deuteroanalogs

direction and magnitude to

the

crystalline

[6, 7, 9, 12, 14-16,

1201

the is

to C,H,D,.

498 cm-l same

and 480

vibrations

confirmed

by

of the

of their shift on passing

phase

[S,

191 the 524.5

Ill. cm-l

Previously band was

1202

Yu. N. PANCHENKO Table 1. Experimental and oaloulated vibrational frequenoios of 1,3-butadiene and its ssvsn deuteromalogs (in cm-l)

CH,=CH-CH=CH,

Y

Assignment of C,H,

1

Y

2

\ y (C-H)

Exptl.

CD,=CH-CH=CD,

Cslo.

Exptl.

Calc.

Exptl.

Calc.

3101

3111

3097

3108

2315

3014

3022

2246

2266

3014

3015

3006

3014

1643

1650

1616

1442

1446

1426

b.

1291*

1294

st.

1206

1208

890

896

613

(=CH,)

Sym.

CH,=CD-CD=CH,

f

st.

st.

Ii:

Enptl.

C&!.

2330

2341

2330

3010

3024

2262

2266

2212

2211

2205

2202

1639

1610

1594

1683

1678

1433

1040

1063

1048

1045

937

942

1296

1298

010

917

1219

1189

1170

1183

1186

1183

-

877

740

735

739

735

610

600

504

457

448

440

442

1013.2

1003

848t

816

955

960

741

751

907.8

906

910

909

728

725

718

720

624.6

619

480

496

397

386

381

382

163

164

-

162

-

149

140

139

967

967

-

803

948

932

796

792

911

906

916

906

728

733

702

707

753

770

(750)

760

610

614

603

601

3102

3110

3098

3109

2350

2329

2336

2329

3066

3069

2240

2246

3041

3041

2256

2246

2986

3000

2984

3009

2228

2209

2215

2204

1699

1613

1696

1587

1535

1550

1523

1610

1386

1393

1377

1376

1031

1036

1042

1036

1296.2

1298

-

1049

13002

1294

1000

999

301 990.6

997

-

937

817

791

770

764

305

-

291

268

267

250

256

[1-W

type

CD,CD-.CD=c

WI

WI

[lo, 201

/ Y (=CH,)

st.

Y (C---c) st. 6 (=CH,)

6

so.

d&-H)

Ag

(

// Y (CC) ,y (=CH,)

r.

6 (C=G-C)

10

\ K’ (C-H)

\

b.

w.

// 11

2 (=CH,)

12

T’ (=CH,)

13

/ \ ‘I (C-C) t. //

14

AU

w.

(

t.

\

\ x’ (C-H)

W.

/ 15

x (=CH,)

w.

16

7’ (=CH,)

t.

17

Y (=CH,)

st.

18

\ Y (CH)

Bg

[

/

st.

/ 19

Y (=CH,)

20

Y (CL&) st.

21

S (=CH,)

22

s\icH)

st. BU

so.

(

b.

// 23 24

p (=CH,) 6 (C=C-C)

I

r. b.

* Corrected on Fermi resonance. t Crystalline pham.

A partial vibrational

reassignment

1203

of 1,3-butadiene

Table l.--continued

CH+D-CH=CH,

Exptl. [ll, 121

Sym. type

I A"

A”

i

A’

\

Calc.

Exptl.

CHD=CH-CH=CH,

CBlC.

PI

Exptl.

Calc.

Y

PO1

3110

3096

3110

3100

3110

3099

3110

1

3041

3054

3040

3043

3048

3060

3049

3044

2

3001

3017

2997

3011

3003

300s

2995

3004

3

1636

1646

1625

1636

1631

1639

1630

1640

4

1427

1440

1418

1419

1409

1421

1427

5

1292

1296

1292

1296

1288

1297

1296

6

1219

1197

1190

1191

1183

1199

-

1183

7

890

888

890

905

793

784

-

829

8

SOS

507

484

476

511

604

-

483

9

992

985

992

985

1008

1001

1009

994

10

908

905

911

905

909

906

908

906

11

498

508

438

434

464

457

491

485

12

-

158

-

153

-

163

-

IS7

13

828

808

792

789

960

966

-

952

14

920

909

711

71s

849

864

815

822

1s

749

769

689

685

674

698

719

740

16

3100

3109

2336

2330

3075

3079

3078

3082

17

2244

2248

2263

2245

3021

3020

3022

18

2984

3005

2216

2209

2286

2266

2283

2270

19

1587

1599

1548

1541

1580

1585

1671

1590

20

1322

1346

1321

21

I

I

Exptl. P3, 201

CHD=CH-CH=CH,

3092

I A’

Cslo.

cia-

trans-

CD,=CD--CH=CH,

-

-

1291

-

1384

1073

1045

-

1023

1007

995

1270

1269

-

1264

22

-

939

735

754

964

964

-

963

23

294

-

293

24

1380

-

297

280

278

288

1204

Yu. N. PANCHENKO

assigned

to

\ //C-H

the

out-of-plane

vibration

Such a small

groups.

of

isotopic

the

shift

of

this band in this series of molecules undoubtedly shows the erroneousness

of the previous

twisting vibrations of the methy-

lene groups (rrs).

The 381 cm-l

spectrum

C&D,

of

the

band in the i.r.

molecule

[lo]

must

assignment [I]

be

the C,D,

corresponding

~rs, which

vibration, spectrum,

with this, the 741 cm-l

of

C,D,

is active

in

in the case of the C,H,

investigation

symmetrical

skeleton

the

mined

Raman

molecule ABE

[20] assigned to it the 760 cm-r line instead of the

[20],

frequency

In the C,D, frequency

vibration of the C,D,

molecule.

The low intensity

of all these lines makes their assignment basis of experimental assistance methods

in

this

data alone difficult.

case is given

of vibrational

by

spectroscopy.

the values of the ~rs vibrations C,H,

and 603 cm-l

sistency

for C,D,

procedure

[22]

on the Definite

from

overtones

molecule

vibrations

be

of the C,D,

approximately

to 300 cm-l,

us to obtain

a

with the experideuteroanalogs

[13] and C,H,D,

assistance

is given

(Table by

CH,=CD--CH=CH, [21].

1).

the i.r.

molecule

In the spectrum

Here

In the case of the double bond the replacement of atoms

of hydrogen

C=C

C,H,D must

bond

and

by deuterium

by

15-25 cm-l

C,H,D,

be expected

over, a type-C

substantial

spectrum

of the

in the gas phase

of this molecule the band

at 828 cm-l.

direction

(992 cm-‘)

band of medium A somewhat

and,

intensity

moreexists

stronger band at 848

in the i.r. cm+ is observed C,H,D, in the crystalline phase.

spectrum

of

Such a con-

siderable isotopic shift of this band in the given series of molecules and its type-C contour provide

considerable extent.

central carbon atoms

and C-D (Table

1).

bonds at the This assignment

is also confirmed by the relatively the corresponding band (995 cm-l) molecule C,H,D,

[20].

Thus

the

data

small shift of in the C,H,D,

on C,H,D,

enable us to return to the vi,, and

and ris

it

system are linked to a

Consequently,

be assigned

vibration of the C,D,

the 1186 cm-l

to the C-C

molecule.

stretching

This is also shown

by the data on the C4H4D2 [21] and CIH,D,

[20]

molecules and by the degree of depolarization the corresponding lines.

of

A small shift of the C-C

stretching lines here in the direction of higher and not lower frequencies

on isotopic

due to the anharmonicity

substitution

is

of the vibrations.

The presence of the 1040 cm-l line in the Raman spectrum

of the C,H,D,

molecule

937 cm-1 line in the Raman [21]

shows

919 cm-1

that

the

of the C,D,

[20]

spectrum

lines

at

and the

of C,H,Ds

1048 cm-l

and

molecule must be assigned

as vs and vs, respectively. For the frequencies vs of the CIH, which are due to the Fermi

bands to the out-of-plane

the

of double bonds and a

828 cm-l

of the C-H

v+, of

Obviously,

that in the case of the C-C

yss of the C,H,D,

and 848 cm-l

(see

molecules).

sufficient justification for assigning the 1013.2 cm-l, vibrations

on the central

bond too, the isotopic shift should not be consider-

line should

[20].

in the 1000 cm--l region is shifted somewhat in the low-frequency

equal

the

for

molecule, the 1013.2 cm-r band

be reassigned

to C,D,,

The use of

In view of the new assignment of the 524.5 cm-l must

The

ascribed to

proved to be too great.

able, since the vibrations

band of the C,H,

of the

reassigned.

molecule [12, 14, 15, 171. The

single bond in a conjugated

C,HsD,

[ IO]-were

of 919 cm--l was previously

frequencies of the ~rs vibrations [ll-121,

of the

some frequencies

must

force field giving good agreement of the calculated

C,H,D

~rs

carbon atoms lowers the frequency of vibration of

in the iterative con-

mental values for the intermediate

the

calculation

of 753 cm-l

enabled

of

vibration

Y(C-C)

yls

[20]

which we had deter-

isotopic shift on passing from C,H,

line to the

of the

AEE

and the frequency

Al?E [20]

603 cm-l

of

In addition, in

also ascribed to ~rs the depolarized line at 753 cm-l. the

band

by

position

deformation

previously

a line at 747 cm-l assigned

by

measured directly. in-plane

BONDYBEY and NIBLICR[5]

the

(140 cm-l)

(250 cm-I)-values

the 686 cm-l line [ 11. We have previously observed [2].

performed

confirm the presence of this band.

vs4 of the in-plane the

modified

molecule which we observed in the infra-

spectrum

twisting

[20].

RICHARDS and

also be assigned to rr,,. The measurements i.r. this

regards

by

red spectrum of the crystalline phase [ 14, 211 must

assigned to the same rla vibration, as is confirmed

As

given

subsequently

SVERDLOV and TARASOVA [19].

by the presence of a 397 cm--l bandin the spectrum of C,H,D,

and

In agreement

assign-

ment and permits this band to be ascribed to the antisymmetrical

frequency NIELSEN

experimental frequencies

spectrum of

molecule and

molecule the shifts are observed of

1276 cm-l

resonance.

liquid and

C,H,

In the [2]

1303 cm-l

the are

observed. In the spectrum of C,H,D [ll], only one line at 1292 cm-1 lies in this region that shows the presence of resonance splitting in case of C,H,.

of frequency

In the region of the vss vibration

1206

A partial vibrational reassignment of l,3-butadiene

of the C,H,D, of

middle

contour) type-A

molecule [20] two bands lie: a band

intensity and

at

a weak

contour).

1335 cm-l band

at

(the

1269 cm-l

The band corresponding

~ss vibration must possess the type-B lie in the region of 1295 cm-l in C,H,

type-B

is equal

to

12962

(the to the

[9].

Thus,

its

deuteroanalogs

energy

distribution

of 1,3-b&+

of potential

[29-311

confirmed the assignment

and kinetic

for these

molecules

given here (Table

1).

Electron diffraction data 1321 [331

Pair of atoms (Fig. I)

) 0.077

) 0.082,

iz;

0.043, 0~061, 0.064, 0.059,

C,=c, C,--c, C,--c, C,--cd

G---H, ‘h--H,

0.0412 0.0467 0.0803 0.062

I

> 0~069, 0.127, 0.060, 0.089; 0.122, 0.144, 0.127, 0.134,

G-H,

C,---H, C&-H, Q--H, C,---K, Cl---H, %--Hz

0.100

The mean amplitudes molecule

calculated

2 and Fig.

data

0.0774 0.0774 0.0778

0.0429 0.0463 0.0609 0.0608

0.0430 0.0466 0.0669 0.0646

0.1046 0.1044 0.1017 0.1068 0.0988 0.1484 0.1429 0.1103 0.1465

0.1061 0.1049 0.1020 0.1086 0.1006 0.1689 0.1563 0.1138 0.1661

of vibration

[32,

of the C,H,

correlation

331.

298”

(Table

with

Somewhat

the

better

agreement is observed for data of work [33]. For the C,H, stants 3).

molecule the Coriolis coupling con-


<:,, ss are also calculated

Very’ good agreement

(Table

with the experimental

Table 3. Coriolis coupling constants (experimental and calculated from vibrational problem) for 1,3-butadiene Exp. 9,[34] 0.46 f 0.03

Calc. 0.48

0.17

0.07

0.64

0.78

spectra of

and its seven deuteroanalogs

that the frequencies of the out-of-plane at 1013.2 cm-r, 624.5 cm-l, of the C,H, 795 cm-l

967 cm-r and 763 cm-1

molecule and the 741 cm-l,

and

603 cm-l

frequencies

770 cm-’

yr4 and ~rs,

molecule the frequencies of 1186 cm-l, and 919 cm-l

us and vs. Previously the

381 cm-r,

of the C,D,

In the case of the in-plane vibrations

of the C,D, 1048 cm-l

shows

vibrations

molecule must be assigned as ore, Q,

[lS]

0.0773 0,0774 0.0778

for given assignment

1) are in good

experimental

T =

T = 0”

experi-

Iv. COlCLUsIOH

mentioned

Calculation

The

A detailed analysis of the vibrational

respectively. Table 2. Mean amplitudes of vibration (experimental and calculated from spectroscopic data) for 1,3butadiene (A)

c&.

as it is noted by the authors of work [9].

1,3-butadiene problem

for

cause of the inaccuracy of the rotational constants

since this vibration cm-l

The solution of the direct vibrational diene and the calculation

here is obtained

contour and

value must be about 1300 cm-l. for six intermediate

result

mental value of &,ss is much less significant be-

must be assigned as Y,,

[12, 14-171 the frequencies

were assigned incorrectly. frequencies

of

and 702 cm-l

of the C,D,

also assigned incorrectly.

In the work

1009 cm-l,

1042 cm-l,

molecule were

Good agreement

of the

mean amplitudes

and the Coriolis coupling

stants calculated

for a new assignment

experimental

data confirms the correctness of the

frequency interpretation. data on the frequencies and

lines

con-

with the

of

the

Thus, the experimental of the prominent

vibrational

spectrum

bands of

1,3-

butadiene and its seven deuteroanalogs

fall within

the framework

model.

of s-transoid

molecular

Aclcnowledgements-The author is deeply grateful to Dr. K. ABE for providing with his experimental data on vibrational frequencies of some deuteroanalogs of 1,3-butadiene before their publication. REFERENCES [II C. RICHARDS and J. NIELSEN, J. Opt. Sec. AmeT. 49, 438 (1960). 121 Yu. N. PDCHENKO, Yu. A. PENTIN, V. I. TY~IN and V. M. TATEVSKII, Optica&x&y 12,488 (1962). 131 E. V. SOBOLEVand V. T. ALEESAXYAN, Zh. atruet. Khim. 4, 627 (1963). 141 V. N. NIKITIN, K. KEEIN-ROBINSON, L. I. MAELAKOV and M. V. VOL’KENSTEIN, Opt. i epektr., Coil. II, Moscow and Leningrad, p. 330 (1963) (in Russian). [51 V. E. BONDYBEY and J. W. NIBLER, Spectrochim. Acta 29A, 646 (1973). 161 Yn. N. PANCHENKO and Yu. A. PENTIN, Proc. Comm. Spar. Acad. Sci., USSR, Report of the XVth Conference on Spectroscopy, July 6-11, 1963, Minsk, Vol I, p. 310 (in Russian).

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1206

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