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Journal of Chemistry
Volume 2013, Article ID 682514, 12 pages
http://dx.doi.org/10.1155/2013/682514
Research Article

On the Relevance of Considering the Intermolecular Interactions on the Prediction of the Vibrational Spectra of Isopropylamine

1Química-Física Molecular, Departamento de Química, FCTUC, Universidade de Coimbra, 3004-535 Coimbra, Portugal
2Departamento de Química, CICECO, Universidade de Aveiro, 3810-193 Aveiro, Portugal

Received 2 May 2013; Revised 19 August 2013; Accepted 18 September 2013

Academic Editor: Anton Kokalj

Copyright © 2013 Ana M. Amado et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

The effects of implicitly considering the effects of hydrogen bonding on the molecular properties, such as vibrational frequencies, were inferred on the basis of DFT calculations. Several clusters of isopropylamine were assembled and theoretically characterized. The results showed that maximum H-bond cooperativity is achieved when the amine group acts simultaneously as donor and acceptor. The effect of H-bond cooperativity manifests itself in the relative cluster stability and on the structural and vibrational frequency predictions. Referring to the vibrational frequencies it was found that the stretching and torsion vibrational modes are the most affected by the amine involvement in hydrogen bonding. Both stretching modes were found to be significantly redshifted relative to the monomer. The torsional mode, on the other hand, was found to be blueshifted up to 350  . Finally, the comparative study between the theory levels performed allows to conclude that the small 6-31G* basis set is able to stabilize weak interactions as long as the new dispersion corrected DFT methods are considered. The impairments observed with conventional DFT methods for describing weak interactions may be overcome with the improvement of basis set, but the associated increase of computational costs may turn the calculations unfeasible.