Molecular mechanics calculations and experimental studies of conformations of .delta.-valerolactone

Abstract

The microwave spectrum of the title compound has been determined in the gas phase at room temperature, and the Raman spectrum has been determined on the liquid at room temperature and on the solid at 73 K. From the experimental data it is concluded that there are two conformers separated in energy by approximately 0.6 kcal/mol, and only the more stable one persists in the crystal. The more stable conformer has a very small (<0.1 D) µ<. component of the dipole moment, while this component is much greater for the less stable conformer. The rotational constants for the two conformations have been determined and are substantially different. The use of the molecular mechanics (mm2) program indicates two stable conformers, a half-chair and a boat form. The former is calculated to be 0.54 kcal/mol more stable and to have a value of µ0 about 0.02 D. The value for µ0 predicted for the boat conformer is approximately 1 D. The rotational constants calculated for the two conformations are in agreement with the experimental ones only if the half-chair conformation is the more stable.

(−)‐R‐Mevalonolactone Studied by ROA and SERS Spectroscopy

“…Moreover, the intensity of the band at 831 cm -1 shows that the contribution of boat conformation is bigger than that calculated for the gas phase. The analogous experimental data were obtained by Philip et al 18 for the related molecule, i.e., δ-valerolactone. In that work, a pair of Raman bands at 748 and 798 cm -1 were found and assigned as the ring-breathing vibrations of the half-chair and boat conformations, respectively.…”

“…Most of the literature is devoted to the analysis of the conformations of unsubstituted δ-lactones, i.e., δ-valerolactone. Its conformation was explored both experimentally by 1 H NMR, 13 C NMR, 40,41 and Raman spectroscopy, 18 and theoretically by MM2, 18,42,43 MM3, 43,44 HF/6-31G*, 41,45,46 MP2 or G3 MP2, 45,[47][48][49] and B3LYP methods with different basis sets. [49][50][51][52] All of these calculated data match the experimental one very well, and show that δ-valerolactone exists in halfchair and a little less stable as boat conformations.…”

“…17 It is known in the literature that a normal Raman effect can be successfully applied in the investigation of compounds containing a δ-lactone ring such as δ-valerolactone or the antimalaria drug artemisinin. 18,19 The prominent bands in the experimental Raman spectrum of mevalonolactone were reported in the 1990s, 7 but to the best of our knowledge neither detailed description of that spectrum nor its simulation by quantumchemical calculations have been presented in the literature.…”

Enantiospecific synthesis of the sugar amino acid (2S,5S)-5-(aminomethyl)-tetrahydrofuran-2-carboxylic acid

“…20,21 Molecular mechanics calculations indicated that these two forms corresponded to the two minimum-energy conformations, with the H conformer being the more stable. 22 The 1 H NMR spectrum of 9 showed large values for J 2,3ax (11.0 Hz), J 4ax,5 (11.4 Hz), and especially for J 3ax,4ax (13.0 Hz) thus suggesting a strong preference of the lactone ring for the 4 H 3 conformer. In this conformation the bulky substituents at C-2 and C-5 are equatorially (or quasiequatorially) oriented.…”

Characterization of low temperature dielectric processes in Poly(dicyclohexyl-itaconate)

“…MM calculations were performed using the force field method developed by Allinger and co-workers [32][33][34][35]. The PC-MODEL software [36] was employed to carry out the calculations.…”