A Raman study of several isotopic derivatives of cyclopentene in condensed states

Abstract

The Raman spectra of various isotopic derivatives of cyclopentene have been studied from 20 U, 293 K as functions of temperature and isotopic substitution. In the solid phase I, two p k s between 130 and 180 cm-l, assigned to the ting-puckering mode, allow the ring-puckering potential function to be determined in the onedimensional approximation. Compared with the gas phase, it shows only a slight increase in the banier height, smaller for monohydrogenated -3hl cyclopentene (Q3H) than for the perhydrogenated cyclopentene (CyHs), and a simullaneous decrease in the puckering angle value, more pronounced for Q3E than for QHS These trends could explain the appearance of a new solid phase I', characterized by a planar contormalion of the cyclopentene ring, in the mullideuterated cyclopsntene derivatives. In the solid I and plastic phases, the u(CH) stretching spectra of monohydrogenated -3h1 (Cy3H) and 4 h l (Cy4H) cyclopentenes show two distinct u(CH) bands assigned U, the CH bond in the axial and equatorial positions. The c o a h n c e of these two bands in the liquid smte indicates an exchange rate behveen the two conformen of about 5 x 10'' s-l at 295 K.

Characterization of C5 Hydrocarbons Relevant to Catalysis

“…Cyclopentene has also been extensively studied. − The molecule is puckered, C s symmetry, and most investigations have been aimed at determining the nature of the ring puckering vibration and the barrier to inversion of the ring. The calculated structure is in reasonable agreement with the limited structural data available for the gas phase − (Table S8, Supporting Information).…”

High Vibrational State Energy Redistribution in Two Deuterated Cyclopentenes

“…In the monohydrogenated nitromethane molecule Δ v = 1 spectrum, this component is the more important of the spectrum and is situated at 15 cm -1 above the transition issued from the fundamental level. In monohydrogenated cyclopentene molecules, the transitions issued from ring-puckering levels above the potential barrier are situated at wavenumbers intermediate between the axial and the equatorial ones . Their intensities are less important than is the case for the nitromethane molecule because the potential has a higher barrier.…”

“…9 When the motion is slow enough with respect to the vibrational energy redistribution, as is the case in cyclopentene molecules, the coupling between the vibrations and the large amplitude motion can be treated in the adiabatic approximation. Indeed, the ring-puckering period is of the order of a few picoseconds 10 which is much slower than the rapid energy flow in cyclopentene. When there are strong Fermi resonances, the characteristic time of the energy flow has been estimated to be less than 100 fs.…”

“…In monohydrogenated cyclopentene molecules, the transitions issued from ring-puckering levels above the potential barrier are situated at wavenumbers intermediate between the axial and the equatorial ones. 10 Their intensities are less important than is the case for the nitromethane molecule because the potential has a higher barrier. For hydrogenated molecules, when the coupling between the CH stretches is effective (normal mode regime), the vibrational energy flows from one CH bond to another in order to minimize its variation during the motion.…”