Vibrational spectra of cyclopropenes. II. IR spectra of 1,2-disubstituted cyclopropenes

Abstract

The IR spectra were measured and the vibrational problem was solved for the 1,2-dimethyl-3-phenylcyclopropene (I) and 1,2-diphenylcyclopropene (II) molecules. The forms of the normal vibrations were determined, and the vibrations associated with vibrations of the exo- and endocyclic bonds of the ring were distinguished. It was shown that substitution at the double bond of cyclopropene leads to a change in the form of the symmetrical vibration of the ring in comparison with the vibration of unsubstituted cyclopropene. It was shown that a significant hypsochromic shift of the band of the symmetrical ring vibration in 1,2-disubstituted cyclopropenes in comparison with cyclopropenes that do not contain substituents at the C1,2 atoms is due chiefly to the kinematic effect of the substituent. It was found that the introduction of substituents at the double bond of the ring leads to a decrease in the force constant of the double bonds.