Matrix isolation FTIR spectroscopic and theoretical study of methyl lactate

Abstract

Methyl lactate [CH(CH 3)OHC(¼O)OCH 3 ] conformational space was investigated by extensive DFT/B3LYP/6-311þþG(d,p) and MP2/6-31þþG(d,p) calculations and matrix-isolation FTIR spectroscopy in argon and xenon matrices. From the seven different conformers predicted by the calculations, two forms (the most stable conformers yielded by the calculations: SsC and GskC, where the letters refer to the conformations assumed by the HOCC, OCC¼O and O¼COC dihedrals, respectively) were observed and characterized spectroscopically. Conformer interconversion pathways were also theoretically investigated. The low calculated barrier associated with the G 0 sk 0 C ! GskC conversion ($1 kJ mol À1) explains the absence of the third most stable form (G 0 sk 0 C) of methyl lactate in low-temperature matrices. Deposition of methyl lactate at different temperatures, together with the theoretical data, aided to the full assignment of the observed spectra. #

Structure and reaction pathways of methyl lactate on Pd(111)

“…The evolution of the infrared spectra with coverage is displayed in Fig. 7 following methyl lactate adsorption at 80 K. The spectrum of the multilayer is essentially identical to that of pure methyl lactate and can be assigned by comparison with the spectrum of matrix-isolated methyl lactate, where the assignments were made by comparison with density functional theory calculations [37][38][39][40]. Methyl lactate can exist in a number of conformations, the moststable of which is the SsC conformation in which the CH 3 -O-(C@O)-C backbone of the molecule is found, by density functional theory calculations, to be almost planar [38], with hydrogen-bonding interactions between the OH and C@O groups.…”

Chirality Recognition between Neutral Molecules in the Gas Phase

“…However, the hydrogen bond involved in the syn form is much stronger than that involved in the skew form. Despite being observed in matrix isolation experiments, [134] the skew isomer of methyl lactate was detected neither in microwave measurements [135] nor in FTIR spectroscopy of jetcooled species. [93,136] As for the ethanolamine complexes, the structures of ahydroxyester dimers calculated at the B3LYP or MP2 level consist of addition or insertion complexes.…”

Chirality Transfer in a Methyl Lactate–Ammonia Complex Observed by Matrix‐Isolation Vibrational Circular Dichroism Spectroscopy

“…Figure 1 shows the experimental MI-IR and VCD spectra obtained for both enantiomers of ML in an argon matrix at a deposition temperature of 10 K. The MI-IR spectrum agrees well with a previous matrix study. [15] The MI-VCD spectra of the two enantiomers show good mirror images and narrow bands, thus allowing a detailed comparison with the calculated spectra. The previous matrix study of ML established that only two of the three theoretically predicted lowest-energy conformations (Supporting Information, Figure S2) contribute to the spectrum at 10 K with contributions of approximately 95 % and 5 %.…”

“…The previous matrix study of ML established that only two of the three theoretically predicted lowest-energy conformations (Supporting Information, Figure S2) contribute to the spectrum at 10 K with contributions of approximately 95 % and 5 %. [15] At 10 K, the third conformer is expected to convert into the second-lowest energy structure, with a low conversion barrier of about 0.5 kcal mol À1 . The experimental and calculated spectra, especially of the VCD spectra, show excellent correlation.…”

“…The two most stable pure ML conformers were determined to have about 95 % and 5 % population in an Ar matrix. [15] Assuming a kinetically controlled formation of ML···NH 3 at 30 K, the two low-energy insertion conformers, that is, conformers 1 and 2, would each contribute 47.5 %, whereas the third conformer contributes 5 %. In Figure 4, the population-weighted theoretical spectra are compared with the experimental spectra obtained for the 1:5 mixtures.…”