Análise conformacional do 1,3-butanodiol e de seus derivados através de cálculos teóricos

Abstract

Theoretical chemistry is the branch of chemistry that has as main tool the resolutions of physical and chemical theories using computational calculations. The resolution of these theories generate data that complement or predict the practical part. One of the virtues of theoretical chemistry is to predict the stability of compounds in certain conformations, which became one of the most used tools for organic chemists, biochemists, among others. The study of the conformations is called conformational analysis, the conformation of a molecule affects various properties and therefore the study of these conformations becomes very important in many fields such as in the study of the active sites of enzymes, protein conformations, stability of the molecule of interest, etc. This work aims to study the influence of intramolecular hydrogen bonding OH···O on conformational equilibria of 3-R-butanol, where R = OH, OCH3, OCH2CH3, OCH(CH3)2 and OC(CH3)3, to check the effect of bulk increasing on the strength of the intramolecular hydrogen bond and consequently the stability of the different conformers in these conformational equilibrium by theoretical calculations. It was used for this study the Gaussian09 software with the DFT theoretical method M06-2X/aug-cc-pVTZ, the AIMALL software for application of the Quantum Theory of Atoms in Molecules (QTAIM), analysis of the Natural Ligand Orbital (NBO) and the study of Potential Energy Surfaces (PES) with the DFT theoretical method M06-2X/6-311++g(df,pd). The results showed that for all compounds studied the structures containing Intramolecular hydrogen bond are directly responsible for the stabilization of these compounds. It was observed that the increase in volume of the R = OH, OCH3, OCH2CH3, OCH(CH3)2 and OC(CH3) group increases charge transfer interaction ηO2 → σ*O1-H1 (3.54; 3.70; 4.03; 3.99 and 4.23 kcal∙mol-1 respectively) due to the inductive effect increased. In addition, despite the increased steric effects with increasing volume of the group R, the structures containing LHI in the compounds with more bulky R group showed greater relevance to stabilize the compound.