Hydrogen Stretching Vibrational Circular Dichroism in Methyl Lactate and Related Molecules

Abstract

The CH- and OH-stretching vibrational circular dichroism (VCD) spectra of methyl lactate and related molecules in CCl4 solution have been investigated to identify solution conformations and establish a correlation between OH- and methine-stretching VCD intensity and molecular structure. Deuterium substitution was used when possible to remove overlapping absorption features in the CH-stretching region. Anisotropy ratios between +2.1 × 10-4 and +2.8 × 10-4 were measured for the methine-stretching VCD of the molecules with both α-oxy and α-CO substituents: (S)-methyl-d 3 lactate, (S)-methyl-d 3 2-(methoxy-d 3)-propionate, di(methyl-d 3) d-tartrate, (S)-methyl-d 3 mandelate, (S)-methyl-d 3 O-(acetyl-d 3)-mandelate, and (S)-benzoin. The methine-stretching VCD intensity serves as a marker for both absolute configuration and solution conformation in these molecules, as previously demonstrated for amino acids and peptides. In (S)-methyl 2-chloropropionate, (R)-methyl 3-hydroxy-2-methylpropionate, and (S)-methyl 3-hydroxybutyrate, the net CH-stretching VCD intensity is small relative to that in the other molecules studied. Ab initio calculations of geometries, vibrational frequencies, and unpolarized infrared absorption (IR) and VCD intensities were carried out to identify the most abundant solution conformers from the VCD spectra and to correlate OH- and methine-stretching VCD intensity with molecular conformations. Factors leading to large methine-stretching VCD anisotropy ratios are assessed.

Confinement of chiral molecules in reverse micelles: FT-IR, polarimetric and VCD investigation on the state of dimethyl tartrate in sodium bis(2-ethylhexyl) sulfosuccinate reverse micelles dispersed in carbon tetrachloride

“…In particular, these absorptions are due to the stretching vibration of OH groups that are hydrogen bonded to either C O or O-CH 3 groups attached to the vicinal chiral carbon [12,13].…”

Matrix isolation FTIR spectroscopic and theoretical study of methyl lactate

“…However, with a single exception, previous experimental studies on this molecule were only able to detect the expectedly most stable SsC conformer [21][22][23]. Experimental evidence of the higher energy forms of MLac was only reported hitherto by Freedman, Nafie and coworkers [24,25], who have studied this compound in CCl 4 solution by vibrational circular dichroism (VCD). These authors examined the C-H and OH stretching spectral regions of the VCD spectrum of MLac and, by comparison with the corresponding calculated spectra obtained at the DFT(B3LYP)/6-31G(d) level of theory, were able to identify in the studied regions spectral features that can be ascribable to the major SsC form and to the two minor conformers having the OH Á Á Á O ester intramolecular H-bond (GskC and G 0 sk 0 C) [24,25].…”

“…Experimental evidence of the higher energy forms of MLac was only reported hitherto by Freedman, Nafie and coworkers [24,25], who have studied this compound in CCl 4 solution by vibrational circular dichroism (VCD). These authors examined the C-H and OH stretching spectral regions of the VCD spectrum of MLac and, by comparison with the corresponding calculated spectra obtained at the DFT(B3LYP)/6-31G(d) level of theory, were able to identify in the studied regions spectral features that can be ascribable to the major SsC form and to the two minor conformers having the OH Á Á Á O ester intramolecular H-bond (GskC and G 0 sk 0 C) [24,25]. To the best of our knowledge no other studies on the conformational preferences and vibrational properties of monomeric MLac have been reported hitherto.…”

“…In this work, the potential energy surface of MLac was reinvestigated at a higher level of theory than previously reported [24] (both the DFT(B3LYP)/6-311þþG(d,p) and MP2/6-31þþG(d,p) levels of theory were used). The structural, energetic and vibrational data obtained theoretically was then used to help interpretation of the matrix isolation FTIR spectra obtained for the compound isolated in solid argon and xenon, enabling the full vibrational characterization of the most stable forms of the studied molecule.…”

How can the Cross‐Link Adducts Formed by Novel Trans Platinum Drug be Influenced by Hydrogen Bond

“…26,27 Excellent agreement between experimental and calculated VCD spectra 27,28 has confirmed the reliability of calculations on metal complexes of moderate size and hydrogen stretching motions, which have been carried out at the DFT level with gauge invariant atomic orbital (GIAO). [28][29][30][31] Meantime, some DFT and ab initio studies concentrated on the molecular properties of cisplatin and its analogues were reported.…”