resumo
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 NH2 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 NH2 torsional mode, on the other hand, was found to be blueshifted up to 350 cm(-1). Finally, the comparative study between the theory levels performed allows to conclude that the small 6-31G* basis set is able to stabilize weak C-H center dot center dot center dot N 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.
palavras-chave
DENSITY-FUNCTIONAL THEORY; H STRETCHING VIBRATIONS; SHIFTED HYDROGEN-BONDS; AB-INITIO CALCULATIONS; DISPERSION CORRECTION; THEORETICAL EVIDENCE; BLUE-SHIFTS; RED-SHIFT; COOPERATIVITY; CLUSTERS
categoria
Chemistry
autores
Amado, AM; Fiuza, SM; de Carvalho, LAEB; Ribeiro-Claro, PJA
nossos autores
Paulo Ribeiro-Claro
Professor Associado com Agregaçãoagradecimentos
The authors acknowledge the financial support from the Portuguese Foundation for Science and Technology-Unidade de Quimica-Fisica Molecular (PEst-OE/QUI/UI0070/2011) and Laboratorio Associado CICECO.