Microwave, r0 structural parameters, conformational stability and vibrational assignment of cyclopropylcyanosilane

• The most stable cis conformer has been identified from microwave spectra.
• Enthalpy difference has been determined between the two forms.
• Adjusted r0 structures were obtained for cis and gauche form.
• Ab initio calculations were performed for the two conformers.

The FT-microwave spectrum (6000–19,800 MHz) of cyclopropylcyanosilane, c-C3H5SiH2CN has been recorded and 773 transitions for the 28Si, 29Si, 30Si, 13C and 15N isotopomers have been assigned for cis and gauche conformers. Infrared spectra (3200–220 cm−1) of gas and Raman spectra (3200–40 cm−1) of the liquid have been recorded as well as the variable temperature (−60 to −100 °C) studies of the infrared spectra of the sample dissolved in liquid xenon. The enthalpy difference between the conformers in xenon solutions has been determined to be 123 ± 13 cm−1 (1.47 ± 0.16 kJ mol−1) with the cis conformer as the more stable form. Approximately 48 ± 2% of the cis form is present at ambient temperature. By utilizing the microwave rotational constants of six isotopomers for cis and seven isotopomers for gauche combined with the structural parameters predicted from MP2(full)/6-311+G(d,p) calculations, adjusted r0 parameters have been obtained for both conformers.

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