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 Title: Molecular electronic environment from methyl torsion and 14n quadrupole coupling Author(s): Gurusinghe, Ranil M. Contributor(s): Tubergen, Michael Subject(s): Spectroscopy of Large Amplitude Motions Abstract: Methyl rotors are sensitive indicators of the local and non-local electronic environment, so a study of methyl torsional barriers at different sites around the perimeter of a conjugated ring system may reveal electronic environment of the indole ring. Previously reported results$^{a}$ are limited to microwave spectroscopic identification of the 1-methylindole, 2-methylindole, 3-methylindole, and 5-methylindole. The new measurements of 4-methylindole, 6-methylindole, and 7-methylindole complete the series. Over one thousand transitions were assigned in the 10.5 – 21 GHz frequency range, resolving both nuclear quadrupole coupling and methyl internal rotation for all seven species. Electronic structure calculations at MP2/6-311++G(d,p) level, torsional barrier calculations and molecular electrostatic potential maps at $\omega$B97XD/6-311++G(d,p) level are used along with the experimental data. $^{14}$N nuclear quadrupole coupling tensor elements were used to determine the ionic character of the NH sigma bond, $\pi$ bonding character of the nitrogen p$_{z}$ orbital, and the amount of negative charge on the nitrogen of each methylindole. Fitted torsional barriers were compared with theoretical investigations of the origin of methyl torsional barriers to confirm that overall barrier arises from both hyperconjugative interactions and structural interactions of bonding and anti-bonding orbitals. \bigskip $^{a}$R. M. Gurusinghe, M. J. Tubergen. 69$^{th}$ International Symposium of Molecular Spectroscopy, Urbana-Champaign, IL, 2014, RJ03. Issue Date: 2016-06-22 Publisher: International Symposium on Molecular Spectroscopy Genre: Conference Paper/Presentation Type: Text Language: En URI: http://hdl.handle.net/2142/91271 Rights Information: Copyright 2016 by the authors Date Available in IDEALS: 2017-01-26
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