Vibrational spectra of cis and trans but-2-enes: assignments, isolated CH stretching frequencies and CH bond lengtsh

Article abstract of DOI:10.1016/0584-8539(85)80149-5

Infrared and Raman spectra have been obtained from 11 isotopomers of cis and trans but-2-enes in various phases (c- and t-CH3CHCHCH3, CH3CHCDCH3, CD3CHCHCD3, CD3CHCDCD3, CD3CDCDCD3; c-CH3CDCDCH3).Nearly all the fundamentals are securely assigned.Isolated CH stretching frequencies ν^is_CH are observed or deduced from the spectra and used to predict CH bond lenghts and dissociation energies.The olefinic CH and methyl CH_s bonds are stronger in the cis compound than those in the trans, in keeping with substituent effects previously observed in propene, and with molecular mechanics predictions.Comparison of ν^is_CH values with local mode fifth overtone spectra for cis-CH3-CH=CH-CH3 indicates that the part of the latter associated with the CH_a bond cannot be readily interpreted.