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Issue 23, 2010
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N-Methyl stereochemistry in tropinone: the conformational flexibility of the tropane motif

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Abstract

The intrinsic conformational and structural properties of the tropinone azabicycle have been investigated in a supersonic jet expansion using rotational spectroscopy. The spectrum revealed the presence of equatorial and axial conformers originated by the inversion of the N-methyl group, with the tropane motif adopting a distorted chair configuration. The determination of substitution and effective structures for the two conformers reveals the flexibility and structural changes associated with the N-methyl inversion, mostly a flattening at the nitrogen atom and a simultaneous rising of the carbonyl group in the axial form. Relative intensity measurements indicate that the conformational equilibrium is displaced towards the equatorial form, with a relative population in the jet of Neq/Nax ≈ 2/1, which would correspond to a relative energy of ca. 2 kJ mol−1 in pre-expansion conditions. Supporting ab initio calculations of the molecular properties and inversion barrier complemented the experimental work.

Graphical abstract: N-Methyl stereochemistry in tropinone: the conformational flexibility of the tropane motif

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Supplementary files

Article information


Submitted
11 Jan 2010
Accepted
12 Feb 2010
First published
19 Apr 2010

Phys. Chem. Chem. Phys., 2010,12, 6076-6083
Article type
Paper

N-Methyl stereochemistry in tropinone: the conformational flexibility of the tropane motif

E. J. Cocinero, A. Lesarri, P. Écija, J. Grabow, J. A. Fernández and F. Castaño, Phys. Chem. Chem. Phys., 2010, 12, 6076
DOI: 10.1039/C000528B

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