Journal of
MOLECULAR
STRUCTURE
ELSEVIER
Journal of Molecular
Structure 41 O-4
11( 1997) 483-488
The vibrational spectra and conformers of chloromethyl
dimethyl chlorosilane
H. M. Jensena, P. Klaeboe”‘*, Gamil A. Guirgisb, V. Aleksaa, C. J. Nielsen”, J. R. Durig”
aDepartment of Chemistry, University of Oslo, P. 0. Box 1033, 0315 Oslo, Norway
bBayer Corporation, Bushy Park Plant, Research and Development Department, Charleston, SC 29208, USA
‘Department of Chemistry, University of Missouri-Kansas City, Kansas City, MO 64110-2499, USA
Received 26 August 1996; accepted 6 September
1996
Abstract
The IR spectra of chloromethyl dimethyl chlorosilane (CH2CI-(CH&SiCI)
were recorded as a vapour and as amorphous and
crystalline solids in the 4000-50 cm-’ range and isolated in argon and nitrogen matrices at ca. 5 K. Raman spectra were
recorded at room temperature and at various temperatures, partly as a super cooled liquid between 295 and 188 K and spectra of
the amorphous and crystalline solids were obtained at 80 K and at 185 K.
The compound exists in anti and gauche conformers, and six IR bands and Raman bands present in the vapour, liquid and
amorphous states vanished upon crystallization. The intensity variations with temperature of four band pairs in the Raman
spectra of the liquid were employed in van? Hoff plots and gave a value of 0.7 -C 0.2 kJ mol-’ for AW(gauche-anti).
The anri
conformer had the lower energy and was also present in the crystal. Only small changes were detected when the matrix spectra
were annealed to 39 K (argon) or 34 K (nitrogen) suggesting a conformational barrier larger than 10 kJ mol-‘.
Ab initio calculations were carried out with the GAUSSIAN 94 program using the basis sets HF/3-21G*, HF/6-31 G*, HF/63 I lG* and MP2/6-31 lG*; optimized geometries, IR and Raman intensities and the vibrational frequencies for the anfi and
gauche conformers were calculated. After appropriate scaling a reasonably good agreement was obtained between the experimental and calculated wavenumbers for both conformers. 0 1997 Elsevier Science B.V.
Keywords:
Conformations;
Vibrational
spectra; Halosilanes;
1. Introduction
Chloromethyl
dimethyl
chlorosilane
(CH$l(CH3)$iC1),
later to be abbreviated
CDCS, has
been synthesized and some physical properties have
been reported by different groups [l-3]. Infrared and
Raman spectra of this compound were first recorded
by Hayashi [4], Batvev et al. [5], Goubeau et al. [6]
and by Kriegsmann and Engelhardt [7] who reported
* Corresponding
author.
0022-2860/97/$17.00
Ab initio calculations
spectral correlations but were not concerned with conformational equilibria. A much more complete infrared and Raman spectroscopic study was published by
Sera and coworkers [8] who studied three halogenated
silicon compounds, one of which was CDCS. These
authors concluded that two conformers were present
for this molecule since six IR bands of the liquid disappeared in the crystal spectrum. The two conformers
(anti and gauche) proposed for CDCS are shown in
Fig. 1.
It was decided to make a new infrared and Raman
0 1997 Elsevier Science B.V. All rights reserved.
PII SOO22-2860(96)09459-g
H.M. Jensen et d/Journal
484
of Molecular Structure 410-41 I (1997) 483-488
Raman spectra of the crystals were observed. Moreover, the conformational
energies, the structure,
the force constants and infrared and Raman intensities were calculated by ab initio methods. Our
preliminary data for CDCS are given in the present
communication.
anti,
gauche,Cl
C,
Fig. I. The anti and gauche conformers
chlorosilane (CDCS).
of chloromethyl
2. Experimental
dimethyl
2.1. Sample preparation
The compound was prepared by the reaction of
trimethylsilane
chloro
with
sulfuryl
chloride,
following the procedure of McBride and Beachell
[2]. Subsequently,
the product was purified in a
low
temperature,
low
pressure
fractionation
column and the purity was controlled
by mass
spectrometry.
spectroscopic study of CDCS and some related molecules CH2X-(CH3)$3iY
(X = Cl, Br; Y = H, F Cl). In
these investigations
the vapour, amorphous
and
crystalline samples in an extended infrared region
were recorded and the infrared matrix isolation technique was also employed. Raman spectra of the
liquids were obtained at different temperatures and
1
..:
. ............
’
I
14bO
.. .
I
I
I
I
I
I
1200
1000
800
600
400
200
Wave number I cm-1
Fig. 2. The Raman spectra of CDCS as a liquid (solid line) and as a crystalline
(dashed line) at 80 K.
H.M. Jensen et al./Journal of Molecular Structure 410-411
(1997) 483-488
485
3. Results and discussion
3.1. Raman spectral results
.
F-==
.
.
0.
.
.
:
.
.
.
.
.
.
4&05
-o,&
mol J-r I -RT
Fig. 3. van’t Hoff plots of the band pairs 612/624, 2961264,
1176 and 1107/l 111cm-’ (from top to bottom).
11831
2.2. Spectral measurements
The infrared and Raman spectrometers and experimental techniques used in this investigation were the
same as those employed for the related molecule
bromomethyl dimethyl chlorosilane [9].
Raman spectra in the region below 1500 cm-’ of
the liquid at ambient temperature, and of the annealed
crystalline solid at 80 K are shown in Fig. 2. A few
bands of the liquid (indicated with asterisks) vanish in
the Raman spectrum of the crystal and they are also
absent in the corresponding
infrared spectrum (see
Fig. 5). The latter bands are attributed to the second
conformer which disappears in the crystal. Since the
number of vanishing bands is small, most of the fundamentals of one conformer presumably overlap those
of the other conformer.
A series of Raman spectra of the liquid were
recorded between 295 and 188 K (the latter temperature represented a strongly super cooled liquid since
the melting point is close to 216 K). In addition polarization data were obtained at ambient temperature.
Slight intensity variations of the bands indicated
with asterisks relative to the neighbouring
bands,
were observed to be temperature dependent, which
wavenumber I cm-r
Fig. 4. Far IR vapour spectrum of CJXS
superposed
by HCl rotational
lines.
486
H.M. Jensen et aDJourna
of Molecular Structure 4/O-4/1
was interpreted as a displacement of the conformational equilibrium. The following band pairs (cm-‘)
were selected: 6121624, 2961264, 1183/l 176 and
1107/l 111, in which the first band of the pair represent the conformer absent in the crystal while the
rprnnrl
(nonm.oll,r
3 n&nhhmw;nn
honA\
tontot;w.=lrr
.L3ti~“LLU \~~‘L~‘U”J
u UrLgn‘“““‘“‘~
uuuu,
WL’LYL.“b’J
is attributed to the conformer present in the crystal.
However, the second band may also have contributions from the high energy conformer making it
unsuited for quantitative
calculations.
A series of
van’t Hoff plots based upon measured peak heights
are presented in Fig. 3, giving the values for AH: 0.7,
0.5, 1.1 and 0.6 kJ mall’ and the average value
AH(gauche-anti)
= 0.7 f 0.2 kJ mall’. Independent
plots based upon integrated areas of the bands in each
pair gave a larger scatter of the points and were not
used in the quantitative calculations. To be discussed
below the low energy conformer, which also is present
in the crystal, is probably anti.
1.0
(1997) 483-488
3.2. Infrared spectral results
Complete vapour spectra were recorded which had
negligible rotational fine structure. A far IR vapour
spectrum in the 350-30 cm-’ region is given in
anrm=A
Fig. A7 . VQ~;~BIE
. _,“UO hanrlr
“U,IUOnhcervc=A
““OUI .“U U6’
“UU xrmll
..“I1 <with
*.11x,thP
&Al”
results from the Raman spectra. The bands with centers at 109 and 72 cm-’ are probably due to the torsional transitions of the gauche and anti conformers
and were observed at 121 and 82 cm-’ in the Raman
spectra of the liquid using the R(v) function. They can
be compared with the corresponding IR transitions at
96 and 67 cm-’ in the vapour phase for the related
compound bromomethyl
dimethyl chlorosilane
[9].
Mid IR and far IR spectra of the amorphous and crystalline solid in the ranges (900-600
and 65050 cm-‘) are shown in Fig. 5. The vanishing bands
(with asterisks) agree with those observed in the
Raman spectra.
..A’.
I %
*
(4
Wave number / cm-’
Fig. 5. (a) Infrared curves (900-600 cm-‘) of the amorphous (solid curve) and crystalline
50 cm-‘) of the amorphous (solid curve) and crystalline sample (dotted) at 80 K.
sample (dotted) at 80 K. (b) Infrared curves (6.50-
H.M. Jensen et al./Journal
of Molecular Structure
,F
“I
tl.,
-,+r:v
LIIC; lllauln
l.‘3lr...,
“z;I”W
?n
L”
Tz
I\
lorl
IS”
tr.
L”
487
(1997) 483-488
3.3. Quantum chemical calculations
IR spectra of CDCS were recorded in argon and
nitrogen matrices (1:500 and 1:lOOO) at 5 and 15 K.
Supposedly, the conformational
equilibrium
of the
vapour phase is maintained when the gas mixture is
shock frozen on the CsI window at 5 K. Careful
,....,,l:“n
aluKxaull~
410-411
The LCAO-MO-SCF
calculations
were performed using the GAUSSIAN 94 program [I 11 with a
variety of basis functions and approximations:
HF/321c_* ) UC,/;
21c* ) UE,/.
,..,1 N#D?,I;
III‘I”-J1”
1u‘,“-JI?1 lP*
I”. 411u
IvITL,“-JI‘1110*
I” -.
The conformational
energies derived from these calculations were remarkably consistent and varied from
6.3 to 6.8 kJ mol-’ with anti being the low energy
conformer. These values are all an order of magnitude
higher than the experimental value 0.7 kJ mol-’ which
was obtained in the liquid.
The Si-C bond was 1.89 6 for both anti and
gauche compared with 1.54 A for a C-C single
bond. The long Si-C distance undoubtedly
contributes to the weak interaction between the two parts
of the molecule, resulting in a low enthalpy difference
between
the conformers
and many overlapping
conformer
bands compared to the corresponding
c.-“11
3111a,,
differences due to relaxation of CDCS in the matrix
lattice. Only small changes were observed in the
band intensities which could be correlated with conformational variations after annealing to temperatures
in the range 20-39 K. Thus, the conformational
barrier is supposedly higher than 10 kJ mall’ [lo],
preventing the high energy conformer converting to
the low energy conformer.
The same conclusion
was drawn from the corresponding
matrix spectra of
bromomethyl
dimethyl chlorosilane
[9]. A barrier
of 17.6 kJ mol-’ was suggested by Sera et al. [S]
from a very uncertain estimation of the torsional
frequency.
098
0.8
I
:
.’
*
,:’
0.0
5
I
600
lb)
I
400
wavenumber / cm-’
Fig. 5. Continued.
I
200
488
H.M. Jensen
Table I
Observed and calculated
600 cm-’ region
Raman liquid
1255
l183* b
1176
1107*
1098
853
825
758
735
693*
685
fundamentals
et al.Nournal
of Molecular
of CDCS in the 1300-
Scaled ab initio”
anti
gauche
1285
1284
1204
Structure
4/O-4/
I (1997)
is probably the low
present in the crystal.
reported variations
solvents of different
483-488
energy conformer which is also
This conclusion agrees with the
in infrared band intensities in
polarity [8].
References
1199
1112
1103
852
821
754
725
849
835
750
736
686
675
a Based upon HF/6-3 11G* and scaling factor of 0.9.
b Bands with asterisks vanish in the crystal spectra.
ethane derivative. No significant changes in the bond
lengths or bond angles between the conformers were
calculated; the dihedral angle of Cl-Si-C-Cl
of the
gauche conformer was 69”.
The force fields in Cartesian coordinates were converted to internal coordinates in the usual manner and
the diagonal force constants scaled with a factor of 0.9
for all wavenumbers above 400 cm-‘, and no scaling
for those below 400 cm-‘. In Table 1 the observed and
calculated wavenumbers of the anti and gauche conformers in a restricted region are presented. As is
apparent, the bands with asterisks fit better with the
calculated gauche fundamentals than with the corresponding anti form. Accordingly, the anti conformer
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