Low temperature FT-IR and molecular orbital study of N,N-dimethylglycine methyl ester: Proof for different ground conformational states in gas phase and in condensed media

Matrix isolation FT-IR spectroscopy and molecular orbital study of sarcosine methyl ester

“…The experimental results indicate that in the matrix the GSC conformer is the most stable conformer, while in consonance with the theoretical predictions the conformational ground state in the gas phase is ASC. These results closely follow data previously obtained for DMG methyl ester [6] and further demonstrate that, for molecules exhibiting different conformers with nearly the same energy, the different strengths of their interactions with the matrix may play a decisive role in defining the order of the conformational states.…”

“…This interaction can take place in both the ASC and GSC conformers and it can then be easily anticipated that these two forms should be the ones with most relevant practical significance. These two conformers are also similar to those experimentally observed for the methyl ester of DMG [6], a compound that was found to present a particularly interesting conformational behaviour, being a notable example of a molecule where the relative stability of the two most stable conformers shows an inversion in going from the gaseous phase to the matrix isolated species [6]. This observation further stimulated us to look at the conformational properties of similar compounds.…”

“…The dipole moments of both GSC (1.87 Debye) and AAC (2.32 Debye) are larger than that of ASC (1.65 Debye) and they are then expected to be stabilized in matrices compared with gas phase. Such stabilization of more polar isomers in matrices relatively to gas phase is a common phenomenon [6,22,23]. Indeed, the results now obtained for sarcosine-Me seem to indicate that for this molecule, like for DMG methyl ester [6], the GSC conformer is stabilized enough to become the most stable conformer in the matrices.…”

“…Such stabilization of more polar isomers in matrices relatively to gas phase is a common phenomenon [6,22,23]. Indeed, the results now obtained for sarcosine-Me seem to indicate that for this molecule, like for DMG methyl ester [6], the GSC conformer is stabilized enough to become the most stable conformer in the matrices. Hence, during the landing of the molecules on the cold substrate, local heating effects due to dissipation of the energy available in the gaseous beam may enable conformational isomerization to take place, leading to an increased population of GSC at expenses of ASC comparatively to the gas phase.…”

“…Since for the methyl ester of DMG the relative stability of the conformers that are the analogous of the ASC and GSC forms of sarcosine-Me was found to be different in the gas phase and in the matrices [6], with the first being the most stable form in the gas and the second (and most polar form) the most stable conformer in the matrices, an estimation of the relative stability of the observed conformers of sarcosine-Me in the matrices was attempted. Taking the DFT results as reference data, the estimated populations (%) for ASC; GSC and AAC; at 298 and 333 K (nozzle temperatures) are, respectively, 52:34:8 and 49:34:9.…”