Two-dimensional potential energy surface for the ring puckering and ring twisting of cyclopentene-d0, -1-d1, -1,2,3,3-d4, and -d8

Abstract

The far-infrared and Raman spectra of four isotopic species of cyclopentene have been assigned in order to obtain a detailed energy map for the low-frequency ring modes. The data for each molecule, consisting of a main series of ring-puckering bands, a series of side bands, and a series of ring-twisting absorption peaks (for the asymmetrically deuterated d1 and d4 molecules), have been analyzed by means of a two-dimensional potential energy calculation. The calculation yields a potential function of V = 7.880 X 10%4 -0.2706 X 10%2 + 0.5158 X 10%2 + 1.904 X 10%%2, where x1 and x2 represent the ring-puckering and ring-twisting coordinates, respectively. The barrier to inversion is calculated to be 232 cm'1 and the sign of the cross term reflects the fact that twisting of the ring tends to hinder the puckering process.

The ring-puckering potential energy function and theoretical calculations for silacyclopent-2-ene-d0 and 1,1-d2 and the difluoro and dichloro derivatives

“…The net result is that each sample winds up with about 95% purity. The 3SCP has a very intense far-infrared spectrum [11] since the positively charged silicon participates strongly in the large-amplitude ring-puckering motion. For 2SCP the far-infrared spectrum is much weaker since its apex carbon atom with the largest amplitude of motion has only a slight charge associated with it [23,25].…”

“…These fall into two groups characterized by C 2v and C s symmetry, respectively, at their planar forms. In the symmetric group of molecules cyclopentene (CP) is puckered with a barrier to planarity of 232 cm À1 arising from the two CH 2 -CH 2 torsional interactions [8][9][10][11]. 2,5-Dihydrofuran (25DHF) [12], 2,5-dihydrothiophene (25DHT) [13], and 3-cyclopentenone (3CPO) [14] are all planar with positive a and b constants in Eq.…”

Study of the photoelectron and electron momentum spectra of cyclopentene using benchmark Dyson orbital theories

“…Depending on the employed basis set, second-order Møller/Plesset perturbation theory (MP2) yields a slightly larger puckering angle 26.3º [80]. On the experimental side, a puckering angle of 23.3±1, 22.3±2 and 29.0±2.5º is inferred from infrared [1], microwave [26,27] and electron diffraction experiments [28], respectively, and a value of 26º has been reported from far-infrared and Raman data [31]. This comparison corroborates the view that, due to shortcomings of the employed functional in the asymptotic region, and limitations of the description of through-space interactions and steric repulsions, B3LYP calculations may somehow drive the molecular structure a little too strongly towards planarity.…”

Determination of vibrational potential energy surfaces from Raman and infrared spectra

“…From these levels a three-dimensional potential energy surface for the puckering (x1), deformation (x2), and rocking (x3) modes of DSCB was calculated. The form of the function is 22 22…”