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Updated: Jun 28, 2025

Free Radicals in Chemical Biology: from Chemical Behavior to Biomarker Development
Published on: April 15, 2013
Identification of Two Stable Side-Chain Orientations of Valine Methyl Ester by Microwave Spectroscopy
Dinesh Marasinghe1, Ranil M Gurusinghe2, Michael J Tubergen1
1Department of Chemistry and Biochemistry, Kent State University, Kent, Ohio 44242, United States.
Abstract:
The rotational spectra of two valine methyl ester (ValOMe) conformers have been measured using a cavity-based Fourier-transform microwave spectrometer in the range of 9-18 GHz. Ten conformers of ValOMe were modeled using the ωB97XD/6-311++G(d,p) level of theory, and separate spectra arising from two lowest-energy conformations were observed and assigned. 44 rotational transitions were assigned to conformer I, the lowest-energy configuration, and were fit to Watson's A-reduced Hamiltonian: A = 2552.0145(5) MHz, B = 1041.8216(3) MHz, and C = 938.54890(22) MHz. 14N nuclear quadrupole hyperfine splittings were resolved, and 231 hyperfine components were fit to χ = -4.187(7) MHz, and χ-χ = 1.269(5) MHz. The spectrum of conformer I also reveals tunneling splittings arising from the methyl rotor. XIAM was used to fit the barrier to the internal rotation of the methyl rotor, and the best-fit V3 barrier was found to be 401.64(19) cm. 47 rotational transitions were assigned for conformer II (ΔE = 2.08 kJ mol-1), and the fitted rotational constants are A = 2544.2837(3) MHz, B = 1092.3654(15) MHz, and C = 896.3131(12) MHz. 264 hyperfine components were fit to χ = -4.187(7) MHz and χ-χ = 1.518(6) MHz, and the best-fit V3 barrier was found to be 409.74(16) cm.
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