Vibrational spectra of cyclopropenes. I. IR spectra of 3,3-disubstituted cyclopropenes

The IR spectra were measured and the vibrational problem was solved for a series of 3,3-disubstituted cyclopropenes [R¹: CH₃; R²: C(CH₃)₃ (I), C₆H₅ (II), CC–C(CH₃)₃ (III), CCH (IV)]. It was shown that a number of vibrations of the cyclopropene ring [symmetrical vibration of the ring, stretching and deformational (planar and out-of-plane) vibrations of the vinyl C–H bonds] are characteristic in frequency and form. On the basis of an analysis of the influence of a substituent at the C³ atom on the force field and the frequencies of the characteristic vibrations, it was concluded that the effect of conjugation of the substituent with _Walsh of the MO of the ring on the distribution of electron density in the ring plays a determining role.St. Petersberg University. Translated from Zhurnal Strukturnoi Khimii, Vol. 34, No. 1, pp. 112–124, January–February, 1993.