AM1 and DFT: Conformational and vibrational spectra analysis of butyl methacrylate

Aim

Butyl methacrylate is used with acrylic products in order to improve the final product according to the desired characteristics. In this work we are about to make an assignment of experimental infrared bands with the help of a theoretical quantum chemistry calculations. The exact knowledge of some bands which are not characteristics of acrylic materials will enable us to make a quick analysis with available techniques of low costs for mixtures of polymers based on acrylate and methacrylate molecules.

Materials and methods

In the experimental part, the infrared spectrum of butyl methacrylate is obtained by using an FTIR Perkin Elmer model 2000. In the computational part and as first step, the theoretical calculations are performed by the semi-empirical AM1 method for excluding similar structures of butyl methacrylate molecule by a meticulous conformational analysis. As a second step the obtained structures are optimized using DFT. The simulated frequencies are then scaled and a tentative assignment is made based on band intensities and PED percentages.

Results

The theoretical calculations predict the existence of five conformations two of them represent the majority of experimental bands in the infrared spectrum. The two less stable structures represent better the band at 546 cm⁻¹, while the assignment is very difficult for the band at 491 cm⁻¹.