The molecular structure of phenetole studied by microwave spectroscopy and quantum chemical calculations

Nguyen, Ha Vinh Lam

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https://hdl.handle.net/2142/91195 Copy

Description

Title

The molecular structure of phenetole studied by microwave spectroscopy and quantum chemical calculations

Author(s)

Nguyen, Ha Vinh Lam

Contributor(s)

• Stahl, Wolfgang
• Ferres, Lynn

Issue Date

2016-06-20

Keyword(s)

Structure determination

Abstract

A pulsed molecular beam Fourier transform microwave spectrometer operating in the frequency range 2 - 26.5 GHz was used to measure the spectrum of phenetole (ethyl phenyl ether or ethoxybenzene, C$_{6}$H$_{5}$OC$_{2}$H$_{5}$). The conformational landscape is completely determined by the orientations of the phenyl ring and the ethyl group. A two-dimensional potential energy surface was calculated at the MP2/6-311++G(d,p) level of theory. Two conformers were found: The trans conformer has a C$_{s}$ symmetry, and the gauche conformer has the ethyl group tilted out of the phenyl plane by about $70^{\circ}$. \newline \indent Totally 186 rotational transitions were assigned to the more stable planar trans conformer, and fitted using a semi-rigid rotor model to measurement accuracy of 2 kHz. Highly accurate rotational and centrifugal distortion constants were determined. Several method and basis set combinations were applied to check for convergence and to compare with the experimentally deduced molecular parameters. The inertial defect of the observed conformer $\Delta$$_{c}$ = (\emph{I$_{c}$} - \emph{I$_{a}$} - \emph{I$_{b}$}) = -6.718 u\AA$^{2}$ confirms that the heavy atom skeleton is planar with two pairs of hydrogen atoms out of plane. All lines in the spectrum could be assigned to the trans conformer, which confirms that the gauche conformer cannot be observed under our measurement conditions. In agreement with the rather high torsional barrier of the methyl group (\emph{V}$_{3}$ = 1168 \wn) calculated by quantum chemical methods, all assigned lines appeared sharp and no signs of splittings were observed for the methyl internal rotation.

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

text

Language

En

Permalink

http://hdl.handle.net/2142/91195

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Copyright 2016 by the authors

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