Analysis of the carbonyl group stretching vibrations in some structural fragments of poly-3-hydroxybutyrate

TL;DR

This study investigates the spectral characteristics of carbonyl group vibrations in poly-3-hydroxybutyrate fragments using quantum chemical calculations and medium effect modeling, improving correlation with experimental data.

Contribution

It combines DFT calculations with medium effect modeling to better explain IR spectral shifts in poly-3-hydroxybutyrate's carbonyl groups.

Findings

Increased chain length causes typical bending in the polymer.

Including medium effects improves theoretical-experimental frequency correlation.

Potential energy curve analysis explains frequency differences.

Abstract

The structure and the medium effects exerted on the spectral characteristics of the carbonyl group stretching vibrations in some structural fragments of poly-3-hydroxybutyrate have been analyzed. Calculations of the equilibrium configurations and IR spectra were carried out using the Gaussian program set in the approximation B3LYP/cc-pVDZ. It has been shown that typical bending of the poly-3-hydroxybutyrate chain is observed with an increase in the number of structural units. In order to explain the difference between the calculated and experimental frequencies of the C=O group stretching vibrations, the calculations of the potential energy curve associated with variations in the length of C=O bond and the subsequent numerical solution of a one-dimensional vibrational Schr\"odinger equation have been performed. The medium effects have been taken into account within the scope of a polarizable continuum model. Owing to the inclusion of the above-mentioned factors, which affect frequencies of the carbonyl groups stretching vibrations, correlation between the theoretical and experimental results has been improved significantly.