Structure and conformation of thioanisole: Gas electron diffraction and contradicting quantum chemical calculations
The geometric structure and conformational properties of thioanisole, C 6H 5SCH 3, have been studied by gas-phase electron diffraction (GED) and quantum chemical calculations. The GED intensities are fitted very well with a single conformer with planar orientation of the S–CH 3 bond ( φ(C–S) = 0°)....
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Published in | Journal of molecular structure Vol. 873; no. 1; pp. 137 - 141 |
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Main Authors | , , , , |
Format | Journal Article |
Language | English |
Published |
Elsevier B.V
17.02.2008
|
Subjects | |
Online Access | Get full text |
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Summary: | The geometric structure and conformational properties of thioanisole, C
6H
5SCH
3, have been studied by gas-phase electron diffraction (GED) and quantum chemical calculations. The GED intensities are fitted very well with a single conformer with planar orientation of the S–CH
3 bond (
φ(C–S)
=
0°). The experimental potential function for internal rotation around the C(sp
2)–S bond derived with a dynamic model possesses a single minimum for planar conformation, but a second shallow minimum for perpendicular orientation cannot be excluded. Calculated potential functions depend strongly on the computational method. The MP2 approximation with small basis sets (6-31G(d)) predict a single minimum for perpendicular orientation, (
φ(C–S)
=
90°), with intermediate basis sets (6-311G(d,p)) an additional shallow minimum for planar orientation and with large basis sets (cc-pVTZ) the global minimum for planar orientation and an additional shallow minimum at
φ(C–S)
=
90°. The B3LYP/cc-pVTZ calculations result in a single minimum for planar orientation, in agreement with the GED experiment. The experimental and calculated barrier to internal rotation is about 1
kcal/mol. The following geometric parameters (
r
a and ∠
h1 with 3
σ uncertainties) were derived:
r(C–C)
av
=
1.395(3) Å,
r(C(sp
2)–S)
=
1.775(4) Å,
r(S–CH
3)
=
1.813(4) Å, ∠CSC
=
104.5(5), ∠C2C1C6
=
119.3(3), ∠C1C2C3
=
120.2(4)°. |
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ISSN: | 0022-2860 1872-8014 |
DOI: | 10.1016/j.molstruc.2007.03.015 |