Conformational Analysis Of Valine Methyl Ester By Microwave Spectroscopy

Marasinghe, Dinesh

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https://hdl.handle.net/2142/116566 Copy

Description

Title

Conformational Analysis Of Valine Methyl Ester By Microwave Spectroscopy

Author(s)

Marasinghe, Dinesh

Contributor(s)

Tubergen, Michael

Issue Date

2022-06-22

Keyword(s)

Large amplitude motions, internal rotation

Abstract

The rotational spectra of two conformers of valine methyl ester (ValOMe) have been measured and assigned using a cavity based Fourier-transform microwave spectrometer in the range of 9-18 GHz as a part of a project investigating the structures of a series of amino acid methyl esters. We modeled 15 possible conformers of ValOMe using the $ \omega$B97XD/6-311++G(d,p)) level of theory. 59 rotational transitions assigned to conformer I were fit to Watson's \textit{A}-reduced Hamiltonian: A = 2552.01(1) MHz, B = 1041.821(2) MHz, and C = 938.549(2) MHz. \textit{$^{14}$}\textit{N} nuclear quadrupole hyperfine splittings were resolved, and the 137 hyperfine components were fit to $ \chi$$_{aa} $ = -4.20(2) MHz and $\chi$$_{bb}-\chi$$_{cc}$ = 1.26(1) MHz. The spectrum of conformer I also reveals tunneling splittings from the ester methyl rotor. The \textit{XIAM}\footnote{H. Hartwig and H. Dreizler, Z. Naturforsch. \textbf{51a}, (1996) 923.} program was used to fit the barrier to the internal rotation of the methyl rotor. The best fit \textit{V$_{3}$} barrier was found to be 387.8(8) cm{$^{-1}$}. 20 rotational transitions were assigned for conformer II and the fitted rotational constants are A = 2544.405(9) MHz, B = 1092.337(2) MHz, and C = 896.301(1) MHZ. The transitions were split by nuclear quadrupole coupling and tunneling, and complete assignment of these components is ongoing.

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

text

Language

eng

Handle URL

https://hdl.handle.net/2142/116566

DOI

https://doi.org/10.15278/isms.2022.WF05

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Copyright 2022 held by the authors

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