Vibrational and electronic investigations, thermodynamic parameters, HOMO and LUMO analysis on crotonaldehyde by ab initio and DFT methods

The energy, geometrical parameters and vibrational wavenumbers of crotonaldehyde were calculated by using ab initio and B3LYP with 6-31G(d,p) and 6-311G(d,p) basis sets. The FT-IR and FT-Raman spectra for liquid state crotonaldehyde have been recorded in the region 3400–400 cm−1 and 3400–100 cm−1, respectively and compared with the theoretical spectrographs constructed from the scaled harmonic vibrational frequencies calculated at HF and DFT levels. The difference between the observed and scaled wavenumber values of most of the fundamentals is very small. Detailed interpretations on vibrational modes have been made on the observed and theoretical spectra and PED for each mode was also reported more precisely. HOMO and LUMO energy levels are constructed and the corresponding theoretical frontier energy gaps are calculated to realise the charge transfer occurring in the molecule. The thermodynamic properties of the title compound have been calculated at different temperatures and the results reveals the standard heat capacities (C0p), standard entropies (S0) and standard enthalpy changes (ΔH0) increases with rise in temperature.

Graphical abstractA complete assignment and analysis of the observed FTIR and FT-Raman spectra of crotonaldehyde based on spectral correlations, electronic structure calculations and normal coordinate analysis have been proposed. Ab initio and DFT calculations have been performed giving energies, optimised structures, NBO charges of the atoms, harmonic vibrational frequencies, IR intensities and Raman activities. Molecular electro static potential, total density distribution and frontier orbital energy levels were constructed.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► The analysis of FTIR and FT-Raman spectra of crotonaldehyde has been proposed. ► DFT calculations have been performed giving energies and optimised structures. ► The stable geometry of the compound has determined from the potential energy scan. ► HOMO, LUMO energies, and Band gap energy were computed. ► Electro static potential and total density distribution were constructed.