SPECTRA AND STRUCTURE OF SMALL RING COMPOUNDS .61. IR AND RAMAN SPECRTRA, VIBRATIONAL ASSIGNMENT, CONFORMATIONAL STABILITY AND AB-INITIO CALCULATIONS OF CYCLOPROPYLMETHYLSILANE
Ts. Little et al., SPECTRA AND STRUCTURE OF SMALL RING COMPOUNDS .61. IR AND RAMAN SPECRTRA, VIBRATIONAL ASSIGNMENT, CONFORMATIONAL STABILITY AND AB-INITIO CALCULATIONS OF CYCLOPROPYLMETHYLSILANE, Spectrochimica acta. Part A: Molecular spectroscopy, 49(13-14), 1993, pp. 1913-1933
The IR (3500-50 cm(-1)) and Raman (3500-20 cm(-1)) spectra of gaseous
and solid cyclopropylmethylsilane, c-C3H5-CH2SiH3, have been recorded.
Additionally, we have obtained the Raman spectrum of the liquid and t
he IR spectrum of the sample trapped in an argon matrix. From these da
ta a complete assignment of the normal vibrational modes is provided.
The spectra of the gaseous and liquid phases have been interpreted on
the basis of the predominance of a conformation having a gauche struct
ure and this form exists exclusively in the solid. Ab initio Hartree-F
ock structural optimizations with the 3-21G and 6-31G* basis sets are
consistent with the gauche rotamer lying similar to 800 cm(-1) lower
in energy than the cis conformation which has the SiH3 group cis to th
e cyclopropyl ring. The force fields obtained with the 3-21G basis se
t have been used to perform a normal coordinate analysis. The cyclopro
pyl torsion has been observed as an IR band of hybrid contour centered
at 80 cm(-1) in the far-IR spectrum of the gas. Combination band spec
tra in the 2300-2000 cm(-1) region of the mid-IR spectrum of the gas c
an be attributed to sum and difference bands of the SiH3 and cycloprop
yl torsional modes with an SiH3 stretching mode. Analysis of these dat
a leads to a barrier governing internal rotation of the silyl group of
687 +/- 50 cm(-1). These results are compared with corresponding quan
tities in some similar molecules.