Raman spectrum and torsional potential function for vinylcyclopropane

Study of the temperature‐dependent conformational averaging of 1H NMR resonances in vinylcyclopropane through the use of ab initio methodology and Boltzmann statistics

“…This is only 0.90 kJ mol 1 lower than the value of 6.96 kJ mol 1 obtained using analytical gradient methods at the 3-21G level of theory, 18 and is in excellent agreement with the 5.98 kJ mol 1 energy difference obtained from spectroscopic measurements. 20 The barrier of rotation between s-trans and gauche conformers obtained at the HF/6-311G ŁŁ level of theory was 13.2 kJ mol 1 , which is similar to the previous theoretical result of 13.3 kJ mol 1 , 18 but 3.2 kJ mol 1 lower than the value obtained from Raman spectroscopic data in the vapor phase. 20 We also investigated if the inclusion of electron correlation in the calculations had a significant effect on the value of the s-trans to gauche energy barrier.…”

“…20 The barrier of rotation between s-trans and gauche conformers obtained at the HF/6-311G ŁŁ level of theory was 13.2 kJ mol 1 , which is similar to the previous theoretical result of 13.3 kJ mol 1 , 18 but 3.2 kJ mol 1 lower than the value obtained from Raman spectroscopic data in the vapor phase. 20 We also investigated if the inclusion of electron correlation in the calculations had a significant effect on the value of the s-trans to gauche energy barrier. Using the structures from the HF/6-311G ŁŁ torsional profile as input, point energies at the DFT (B3LYP hybrid functional) and MP2 levels were computed, employing in both cases a 6-311G ŁŁ basis set.…”

“…The reported values for the increased stability of the s-trans over the gauche conformer are in the 6-7 kJ mol 1 range, and the barrier of rotation between s-trans and gauche forms has been determined from ab initio studies and Raman spectroscopy to be 13.3 and 16.4 kJ mol 1 , respectively. 18,20 The VCP torsional energy profile for rotation around the C-3-C-4 bond derived from dihedral angle driving at the HF/6-311G ŁŁ level of theory obtained from our studies is shown in Fig. 2.…”

Single-crystal X-ray geometries and electron density distributions of cyclopropane, bicyclopropyl and vinylcyclopropane. I. Data collection, structure determination and conventional refinements

“…The studies available for VCP in solution or in the gas phase show a clear preference for the trans-bisected conformation, but do not give detailed information on the molecular geometry [~H NMR: De Mar~ & Lapaille (1980); electron diffraction: Tra~tteberg (1983); Raman: Carreira, Towns & Malloy (1978)]. …”

Enamines. III. A theoretical and photoelectron spectroscopic study of the molecular and electronic structures of aziridine enamines

“…Gaseous formylcyclopropane is known to exist predominantly as a mixture of transand cis-bisected forms (corresponding to conformations I1 and III) [27], in which there are optimum n-type donor-acceptor interactions between the cyclopropyl and the carbonyl groups. Substitution of the carbonyl by the less electronegative vinyl group allows a gauche form (corresponding to conformation I) to compete effectively with a trans-bisected form, the gaucheltrans ratio being approximately 1:3 [28] to 1:7 [29] for vinylcyclopropane in the gas phase. Replacement of the cyclopropyl methine unit by a N-atom then shifts the equilibrium towards the gauche form as a result of increased stabilization of conformer I by enamine-type conjugative interactions and decreased stabilization of conformer II due to the reduced donating power of the three-membered ring system via (wA, n)-type interactions.…”