Vibrational circular dichroism study of (2S,3S)-dideuteriobutyrolactone. Synthesis, normal mode analysis, and comparison of experimental and calculated spectra

Abstract

McGhie, A. R.; McCauley, J. P.; Smith, A. B.; Hochstraseer, R. M. J. Phys. Chem. 1991,95,6075-6078. (47) Letokbw, V. S. In h e r spectmcopy of highly vibrationally excited molecules; Lctokhov, V. S., Ed.; Adam Hilga: New York, 1989; pp 1-54. (48) Hare, J. P.; Kroto, H. W.; Taylor, R. Chem. Phys. Lett. 1991,177, 394-398. (49) Levine, R. D.; Banetein. R. B. In M d c c~l a r Reaction Dynamics andThe preparation, characterization, infrared ahrption, and vibrational circular dichroism (VCD) spectra of the title compound are presented. From ab initio quantum mechanical energy minimization, geometry optimization calculations, the lowest energy conformation is a slightly distorted envelope form, so that deuteration give rise to both pseudoaxially and pseudoequatorially substituted conformers. The vibrational spectra (IR and Raman) have been assigned by comparison of frequencies and overall intensity patterns to those calculated by using an ab initio force field obtained for both conformers. This force field was subsequently modified by refining scale factors to improve the fit to frequencies of assigned bands for both the do and d2 isotopomers. The absorption intensities and VCD signs and magnitudes were calculated by the ab initio magnetic field perturbation theory of Stephens using the distributed origin gauge with origins at the nuclei. Good qualitative agreement was found between the experimental and theoretical dipole strengths and rotational strengths when the average of the calculated valuar for the two conformers was used. The best calculations used a 6-31G** basis set for for the force field and the intensities, but the refined force field did not lead to a significant improvement in the intensity or VCD pattern (other than frequency alignment) as compared to the unscaled ab initio result. For purposes of comparison to previous reports, calculations were also made for the planar conformation. Test calculations with variants of more approximate methods that do not allow for charge reorganization associated with nuclear motion gave distinctly unsatisfactory results, particularly in the mid-infrared portion of the spectrum.

Computational Study of γ-Butyrolactone and Li+/γ-butyrolactone in Gas and Liquid Phases

“…This conclusion agrees with the expectation of Cremer and Pople in their study on general monocyclic rings, 35 according to which a planar ring should imply a more highly strained ring angle at the carbonyl atom than a twisted conformation. Regarding other dihedrals (Table 4), our results are very similar to previous ab initio calculations 18 Some final remarks can be made on the structure: the carbonyl bond axis (O 1 -C 1 ) is slightly tilted (3°) with respect to the bisetrix of the C 2 -C 1 -O 2 angle, which results in a distance among the two oxygens shorter than the O 1 -C 2 separation. For what concerns the hydrogen atoms, differences in their distances from the carbons (∼1.09 Å), or in the H-C-H bending angle (∼109°) are negligible.…”

Vibrational Optical Activity of (3S,6S)-3,6-Dimethyl-1,4-dioxane-2,5-dione

“…Thus the lactide could be seen as a case where VCD is less sensitive than the absorbance to improvement in the level of calculation. We have seen this behavior in other systems 11,13 and attribute it to the VCD having a strong dependence on the relative geometry of interacting local dipoles induced in the normal mode arising from the dependence of the rotational strength on the scalar product of the electric (µ) and magnetic (m) transition dipole moments, R ) Im(µ‚m).…”

“…Our previous studies have focused on 3-, 4-, and 5-membered-ring molecules with increasing complexity of the hetero-atoms. Of most direct relevance to the lactide, the previously studied γ-butyrolactone molecule provided an unduly complex system because of the flexibility of its 5-membered ring 13 while four-membered oxygen-containing rings yield straightforwardly interpretable spectra. 2, 14 The results shown here clearly demonstrate that the theory convincingly agrees with the experiment for this six-membered-ring molecule with one stable conformation.…”

“…limited basis set computations). This compound belongs to a series of C 2 symmetry , and related model compounds that we and others − have studied in an effort to develop procedures for determination of molecular structure on the basis of such optical activity measurement. However, it goes beyond those previous studies in being one of the simplest oligomeric molecules we could study that is closely related (isoelectronic) to the oligopeptide conformational problems of wide interest.…”

Vibrational Optical Activity Study of trans-Succinic-d2 Anhydride

“…Vibrational circular dichroism (VCD) can be calculated for a number of small molecules using the magnetic field perturbation (MFP) model as formulated by Stephens . We have applied it on the ab initio quantum mechanical self-consistent field (SCF) level to several model systems made chiral by deuteration, such as (3 R ,4 R )-3,4-dideuteriocyclobutane-1,2-dione and (2 S ,3 S )-2,3-dideuteriobutyrolactone . For those cases, however, scaling of the harmonic force field was necessary to achieve a reasonable agreement between simulated and experimental VCD spectra.…”