Preprint Article Version 1 Preserved in Portico This version is not peer-reviewed

Quantifying Conformational Isomerism in Chain Molecules by Linear Raman Spectroscopy: The Case of Methyl Esters

Version 1 : Received: 30 June 2021 / Approved: 1 July 2021 / Online: 1 July 2021 (14:22:39 CEST)

How to cite: Gawrilow, M.; Suhm, M.A. Quantifying Conformational Isomerism in Chain Molecules by Linear Raman Spectroscopy: The Case of Methyl Esters. Preprints 2021, 2021070033 (doi: 10.20944/preprints202107.0033.v1). Gawrilow, M.; Suhm, M.A. Quantifying Conformational Isomerism in Chain Molecules by Linear Raman Spectroscopy: The Case of Methyl Esters. Preprints 2021, 2021070033 (doi: 10.20944/preprints202107.0033.v1).

Abstract

The conformational preferences of the ester group have the potential to facilitate the large amplitude folding of long alkyl chains in the gas phase. They are monitored by Raman spectroscopy in supersonic jet expansions for the model system methyl butanoate, after establishing a quantitative relationship to quantum-chemical predictions for methyl methanoate. This requires a careful analysis of experimental details, and a simulation of the rovibrational contours for near-symmetric top molecules. The technique is shown to be complementary to microwave spectroscopy in quantifying coexisting conformations. It confirms that a C-O-C(=O)-C-C chain segment can be collapsed into a single all-trans conformation by collisional cooling, whereas alkyl chain isomerism beyond this five-membered chain largely survives the jet expansion. This sets the stage for the investigation of linear alkyl alkanoates in terms of dispersion-induced stretched-chain to hairpin transitions by Raman spectroscopy.

Subject Areas

Raman intensity; anharmonicity; conformational isomerism; chain folding; jet cooling; rotational band contour; esters

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