Density functional theory, comparative vibrational spectroscopic studies, NBO, HOMO–LUMO analyses and thermodynamic functions of N-(bromomethyl)phthalimide and N-(chloromethyl)phthalimide

Quantum mechanical calculations of energies, geometries, and vibrational wavenumbers of N-(bromomethyl)phthalimide and N-(chloromethyl)phthalimide are carried out using density functional theory (DFT/B3LYP) method with 6-31G and 6-311G(d,p) basis sets. The optimized geometrical parameters obtained by B3LYP method show good agreement with experimental data. The difference between the observed and scaled wavenumber values of most of the fundamentals is very small. A detailed interpretation of the infrared and Raman spectra of N-(bromomethyl)phthalimide and N-(chloromethyl)phthalimide was also reported. The calculated HOMO and LUMO energies show that charge transfer occurs in the molecules. The thermodynamic functions of N-(bromomethyl)phthalimide and N-(chloromethyl)phthalimide have been performed at B3LYP/6-31G and B3LYP/6-311G(d,p) basis sets. The theoretical spectrograms for FT-IR and FT-Raman spectra of N-(bromomethyl)phthalimide and N-(chloromethyl)phthalimide have also been constructed.

An extensive study on the vibrational, structural, thermodynamic characteristics as well as the NBO analysis of N-(bromomethyl)pthalimide(BMP) and N-(chloromethyl) pthalimide were carried out using DFT/B3LYP/6-31G method. The calculations reveal that CH2Br and CH2Cl moiety is responsible for the non-planar structure favoring C1 symmetry. The NBO analysis confirms the hyperconjugation interaction.Figure optionsDownload as PowerPoint slideHighlights
► The complete data of N-bromo methyl pthalimide and N-chloro methyl pthalimide provide useful information for the study of substituted pthalimides.
► The influence of methylene groups on the geometry of pthalimide and its normal modes of vibration have been discussed.
► The HOMO–LUMO energy gap reveals the chemical stability of the molecule.
► The difference in thermodynamic parameters between the title compounds seems to be insignificant.