Vibrational frequencies for silaacetylene and its silylidene and vinylidene isomers

Journal Article · Wed Mar 09 00:00:00 EST 1983 · J. Am. Chem. Soc.; (United States)

DOI:https://doi.org/10.1021/ja00343a002· OSTI ID:5555441

Hoffman, M R; Yoshioka, Y; Schaefer, III, H F

The molecular structures, vibrational frequencies, and relative energies of silaacetylene and its vinylidene and silyidene isomers have been investigated via nonempirical molecular electronic theoretical methods. Basis sets of double Zeta (DZ) and double-Zeta plus d function quality have been used for this purpose in conjunction with self-consistent-field (SCF) and configuration interaction (CI) wave functions. The largest CI included in a completely variational manner 8 001 configurations, and analytic CI gradient methods were used to determine the structure and harmonic vibrational frequencies of silaacetylene itself. The absolute minimum on the potential energy hypersurface is the silyidene, :Si==CH/sub 2/, which lies approx.50 kcal below the linear silaacetylene. The vinylidene isomer H/sub 2/Si==C: is either an extremely shallow minimum, or, more likely, not a genuine relative minimum at all. Silaacetylene is predicted to have a trans bent equilibrium geometry, with HSiC angle 128.8/sup 0/, HCSi angle 150.1/sup 0/, and a silicon-carbon bond distance of 1.635 A about 0.08 angstrom, about 0.08 angstrom shorter than a ''standard'' Si==C double-bond distance. The silicon-carbon stretching vibrational frequency is predicted to be approx. 1100 cm/sup -1/, or 10% higher than found experimentally for dimethylsilaethylene. It is concluded that the silicon-carbon linkage in trans-bent silaacetylene is intermediate between a double and triple bond. There appears to be no cis isomer of silaacetylene.

• Research Organization: Univ. of California, Berkeley, CA (United States)
• OSTI ID: 5555441
• Journal Information: J. Am. Chem. Soc.; (United States), Vol. 105:5
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
ACETYLENE
VIBRATIONAL STATES
ALKYNES
SILICON COMPOUNDS
STRUCTURAL CHEMICAL ANALYSIS
VINYL MONOMERS
CONFIGURATION INTERACTION
ISOMERS
WAVE FUNCTIONS
ENERGY LEVELS
EXCITED STATES
FUNCTIONS
HYDROCARBONS
MONOMERS
ORGANIC COMPOUNDS
400301* - Organic Chemistry- Chemical & Physicochemical Properties- (-1987)