Issue 39, 2010

Conformational equilibria in vanillin and ethylvanillin

Abstract

The conformational equilibria of vanillin and ethylvanillin have been investigated in a supersonic jet expansion using rotational spectroscopy. Two conformers have been detected for each molecule, with a dominant O–H⋯O intramolecular hydrogen bond locking the local conformation of the hydroxyl and methoxy/ethoxy groups. As a consequence, the observed conformers of vanillin differ only in the orientation of the aldehyde group, either cis or trans with respect to the methoxy group. For ethylvanillin the ethoxy group would plausibly generate additional trans (in-plane) or gauche (out-of-plane) orientations. However, the two detected conformations exhibit only planar ethoxy trans arrangements, with the gauche forms most probably depopulated by collisional relaxation in the jet. Torsional tunneling effects due to internal rotation of the terminal methyl groups were not detectable, indicating internal rotation barriers above 12.3 kJ mol−1. The conformational population ratios in the jet have been estimated from relative intensity measurements. Ab initio (MP2) and DFT calculations using B3LYP and the recent M05-2X empirical functional supplemented the experimental work, describing the rotational parameters, conformational landscape and the aldehyde and methyl internal rotation barriers in these molecules.

Graphical abstract: Conformational equilibria in vanillin and ethylvanillin

Supplementary files

Article information

Article type
Paper
Submitted
16 May 2010
Accepted
15 Jul 2010
First published
19 Aug 2010

Phys. Chem. Chem. Phys., 2010,12, 12486-12493

Conformational equilibria in vanillin and ethylvanillin

E. J. Cocinero, A. Lesarri, P. Écija, J. Grabow, J. A. Fernández and F. Castaño, Phys. Chem. Chem. Phys., 2010, 12, 12486 DOI: 10.1039/C0CP00585A

To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Social activity

Spotlight

Advertisements