Infrared and raman spectra of methyl thiocyanate and conformations of some alkyl thiocyanates and isothiocyanates

Journal of X~olecular Structure, 115 (1984) 391-396 Elsemer Science Publishers B.V., Amsterdam -Printed

INFRARED

AND RAMAN SPECTRA OF METHYL THIOCYANATE

THIOCYANATES

J.

F.

391 In The Netherlands

AND ISOTHIOCYANATES

SULLIVAN,

Department

AND CONFORMATIONS OF SOME ALKYL

H.

of

L.

HEUSEL and J.

Chemistry,

R.

University

DURIG

of

South

Carolina.

Columbia

SC 29208

(USA)

ABSTRACT The infrared spectra (3200-40 cm-l) of gaseous and solid methylthiocyanate cm-l) of the 1 iquid and sol id have been recorded. and the Raman spectra (3200-10 is presented based on group frequencies, A complete vibrational assignment From the and Raman depolarization values. infrared gas phase band contours, it is clear that there are at least two infrared and Raman spectra of the solid, The spectral results will be discussed and molecules per primitive cell. compared to other al kyl thiocyanates and isothiocyanates.

INTRODUCTION Our

recent

vibrational

reinvestigate (refs.

the

2-4)

and

in

microwave

Cal/mole (ref.

for 4)

also

a

liquid)

to

However,

as

the

methyl

seems

the

torsion

Therefore,

including

the

reported

by

because

results.

far has

and,

in

a more

to

in

the

vibrational

infrared

order

previously

were

recorded

9). would

for

the

spectrum

spectrum

not

131

2 80

of

been

the

(ref.

and

and the

a

barrier cm-l

band

have

to

be at

least

V3

to

agree

of

reported.

CH$CN

of

The

results

Flygare the 10)

(-131

1200

cm

the

-1 ,

cal/mol.

probaDly

8% of

has been

the

an

1590

(ref.

is

with

and

In

predicted

sol id

131

the

of

and

Miller

the

to

for

10).

Lett

cal/mol

us

microwave

a barrier

study,

Fateley -1 in cm

solid

prompted

reported

calculated

recent

calculated

(ref.

V6 value

large,

_

been

calculation

3)

1600 -1

cm at

and

Crowder the

be

153

centered

1)

Several

have

constant

(ref_

torsion

out

studies

al.

at

(ref.

methylthiocyanate.

et

be

band

of

force

barrier

to

methyl

pointed

which

the

weak

unreasonably

solid,

rotation

transition

broad,

a

Nakagawa

determined

v = 0 -f v = 1 assigned

to

addition

methyl

ethylthiocyanate

5-9)

(refs.

analysis,

the

of

spectrum

vibrational

CH3SCN molecule early

analysis

vibrational

not which

V3,

microwave

reinvestigated

Raman spectrum of

this

of

study

the are

herein.

EXPERIMENTAL Raman with

spectra

a Spectra-Physics

recorded

by

-77K

boiling

by

0022-2860/84/$03

condensing

model the

nitrogen.

00

on

a Cary

171argon sample

onto

Mid-infrared

0 1984 Elsencr

ion a

model

82

laser.

spectrophotometer

The

blackened spectra

Science Pubhsher;

spectrum brass

of B-V.

the

block gas

of

equipped the

solid

maintained and

solid

was at were

392 recorded cell

on a Digilab

equipped

maintained solid

FTS-14C

with at

CsI

-77K

were

was recorded

12.51.1 beamspl

Fourier

windows

transform

and

used,

a low

interferometer,

temperature The

respectively.

on a Digilab

FTS-15B

Fourier

in uhich

cell far

with

a CsI

infrared

transform

a 10 cm

substrate

spectrum

of

interferometer

the

using

a

itter.

RESULTS The in

spectral

Table

1

published 8)

and

assigned

may

case,

it

is

surprising

frequency

shift

concurrence which

apparently

(190 -1

+ 467 = 657

Cm

in

the

199

the

C-S-C

torsion

of

the

is

in-plane

gas

of

vg

in

band

far

at

as

153

this

vibration.

was

also

conducted

cm-l

213

on the cm”,

of cm

line

A close

have

the -1

examination

no bands

which

studies

of

of

vg + vI0

band

cm-’

at

652

cm-l

in

gas phase, cm

-1 .

band

it

Crowder

observed

the

and

(ref.

4)

far

is

a very barely at

-200

where

the line

infrared

be assigned

of

assigned

cm-I

213

the

could

in

616

is

cm-I

the of

large

The Raman counterpart

190

study

the

at

contour

solid,

.

assigned

the

have

and

at

microwave

in

A-1

cm

is

at657

be -444

we also

center

and 199

we

band

692

rather

broad

shoulder

must

and

its

a moderate

but

phase

spectrum

at

weak

the

this

observed,

centered

of

combination gas

460

infrared

Based

at

the

the

a

also

the

this

this

combination

appearance and

but

components

bend.

solid

at if

has

band The

solid.

the

From the

of

a B-type

the

well

the

solid.

to

were

very

observed

predicted

9),

of

centered

have

of

with

P-branch

However,

We

data (ref.

spectrum

We concur the

stretch

liquid.

the

Moritz

infrared

band

symmetric

the

(ref. -1 cm in

weak

the

two

band

C-S-C

frequency,

In

phase

torsion

a very

stretch.

presented

with

warranted.

that

symmetric

are

well

stretch.

appears a B-type

to

652

the

this

into

was

solid

to

are

of

study

frequency

near

cm-l

the

agree

1_n the

cm-l

it

R-branch

gas

explains

of

comments

705

molecule

data

antisynmetric

C-S-C

spectrum

the

spectral

data,

the

that

shifts

distinguishable. -1 cm is Split

C-S-C

the

methylthiocyanate

at

spectral

the

cm-‘)

observed

the

the

to

infrared

that

centered

Crowder’s

Raman spectrum

band

some minor

from

with

9)

only

with

assigned

(ref.

and

overlap

be

weak

Our

our

can

appears

2.

to

from

which

the

the

and

band

it

and,

band

-

for

1

an A-type

assignment type

obtained

Figs.

previously

observed

gas

data

and

to

methyl in

ths

spectrum

to

the

methyl

cbserved.

DISCUSSION Our

structural

halogen

linkages

isocyanates

12)

isomerism

vibrational

evidence

(ref.

(ref.

rotational the

and

for

data the

vibrational 11) and about on

existence

have

recently

been

isothiocyanates the these of

Ce-N

more

than

of

IVA

extended

(refs.

molecules one

compounds to

conformer,

which

it do

with

include

13,14)

In general,

bond.

types

Group

has not

been yield

presumably

pseudo-

those can

al kyl exhibit

found

that

conclusive because

of

i i0 WAVENUMBER

hi’1

Fig.

1.

Raman spectra

Fig.

2.

Far

the

rather

large

moiety.

However, should

loo”,

phases

and

high

1.68

i

energy

0.07

0.03

only

trans

10% of

It

we have

determined

molecules

larger.

are

preference are

for

consistent

amount study

due

of of

the

to the with trans

CH3CH2SCN,

by

AH most

that

the

in

the

only

both

al.

large the

the the

gas gas

microwave is

results present

one conformer

and

liquid

(ref. in

the

the

has been

gas liquid

state. 15)

gas found

in

that

in

the

choice

in

phases are

and

the

only In

of

for

that liquid because

a number

considerably

liquid

phase

be

0.49

estimated

Thus,

phase.

to of

be higher

values

the

gauche

value

uhose is

liquid

the

in the

7)

may even

phases

between

in

determined the

case in

stable

conformation

phase

the

exist

been

it

of

different

indeed

more

C-K=X

order

than

(ref_

trans

interactions form

has

Ati value,

gas

is

the

much larger

et

differences

symmetric

conformer

phase

is

our in

the

between

liquid

the

cases,

the

conformers

two

the

the for

This

exist

values

spectra

phases.

AH for

of

on

that

which

From

dipole-dipole more

the

of

are

fluid

Hirschmann

molecules that

the

We believe

values

the

in

in

vibration

angles

vibrational

difference

& 23 cm-l)

of

C-S-C

found

the have

enthalpy

incorrect.

possible

and,

in we

conformers (586

was

phase.

is

which

reported

bands

about

present

for

methylisothiocyanate.

amplitudes

uhose different

are

The

(6)

methylthiocyanate.

and

significantly

kcal/mol

kcal/mol

conformers

of

(-140-150°) thiocyanates,

1).

and solid

solid

al kyl

they

(ref.

(A) of

angle

ethylthiocyanate

fluid

f

when

liquid

spectrum

exhibit

conformers for

of

infrared

phase

along these a very

contrast

vibrational

AH

with

a

results small to

the

spectra

39~-

(.i

E

U

o

o

u

u

E

T-

T-

o

,~ u °~ r-

N

U °~

g Ill U

o~

~ --r-

3

O

O

°~

395

EE

E

n

P

Ii-

Ii-

:

5

396 of

CH3CH2NCO

(ref.

(CH3)2CHNCS

(ref.

very

C-N=C

large

“bouna”

states

shown

phase

but

nitrogen it

to

their

much

isocyanates

and

conformer

second

Presumably,

this

simplistic

Cs symmetry, of

“pseudo

as

angles,

the

are fluid

same structural and

whereas

the

of

two

be

(ref.

of these that the

there

for

the

unique

and

phases

from

the

these

large

it

is

between

many of

it

has

in

the

gas

lone

pair

on

atoms

makes

molecules

with

molecules

with

CNC angles

thus

their

not

14),

and carbon

thiocyanate

and have

spectra

present

Certainly

preference

to

are

(ref.

nitrogen

the

12))

molecules

microwave

conformers

small. the

opposed

vibrational

spectrum (ref.

all

From

we believe

difference

characteristic

Cgv symmetry”

very

between

conformational

isothiocyanates, in

may well

have

are bond

Therefore,

CSC

the

the

the

molecules. smaller

molecules

double

compare

it

(CH3)2CHNCO

cyclopropylisothiocyanate

differences

formal

17), However,

configuration. and

these

energy

the

thiocyanate

of

and

linear

18,19)

(ref.

phases.

(>138“)

the

both

their and

difficult

the

angles

(refs. that

CH3CH2NCS

in the fluid

below

vinylisocyanate been

16), 13)

possible

vibrational

in to

ai kyl detect

spectra.

CH SCN and CH3NCS leads to 3 of CH3SCN which exhibits

spectrum

CH3NCS has

been

best

interpreted

in

terms

20).

ACKNOWLEDGMENT The the

authors

National

gratefully Science

acknowledge

Foundation,

Grant

the

financial

support

of

these

studies

by

CHE-82-15492.

REFERENCES 1 2 3 4 5. 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

J. R. Durig, 3. F. Sullivan and H. L. Heusel , J. Phys. Chem., in print. C. I. Beard and B. P. Dailey, J. Am. Chem. Sot. . 71 (1949) 929. S. Nakagawa, T. Kojima, S. Takahashi and C. C. Lin, J. Mol. Spectrosc., 14 (1964) 201. R. G. Lett and W. H. Flygare, J. Chem. Phys., 47 (1967) 4730. F. A. Mi 1 ler and W. B. White. Z. Electrochem. . 64 (1960) 701. N. S. Ham and J. B. Willis, Spectrochim. Acta; 16 (1960) 279. R. P. Hirschmann. R. N. Kniselev and V. A. Fassel. ~ Soectrochim. Acta. 20 . (1964) 809. . A. G. Moritz, Spectrochim. Acta, 22 (1966) 1021. G. A. Crowder, J. Mol. Struct., 7 (1971) 147. W. G. Fateley and F. A. Miller, Spectrochim. Acta, 17 (1961) 857. J. M. R. Jalilian, J. F. Sullivan and J. B. Turner, J. Raman R. Durig, Spectrosc., 11 (1981) 459, and references therein. J. R. Ourig, K. J. Kanes and J. F. Sullivan, J. Mol. Struct. , 99 (1983) 61. T. S. Little, private communication. J. R. Durig, A. B. Nease, J. F. Sullivan, Y. S. Li and C. J. Wurrey, J. Chem. Phys., submitted. A. Bjdrseth and K. M. Marstokk, J. Mol. Struct., 11 (1972) 15. D. T. Ourig, private communication. J. R. Ourig, H. L. Heusel, J. F. Sullivan and S. Cradock, Spectrochim. Acta, submitted. A. Bouchy and G. Roussy, J. Mol. Spectrosc., 68 (1977) 156. C. Kirby and H. W. Kroto, 3. Mol. Spectrosc., 69 (1978) 216. J. R. Durig, J. F. Sullivan, H. L. Heusel and 5. Cradock, J. Mol. Struct., 100 (1983) 241.