α-Bromo-p-tolunitrile: Conformational stability, vibrational spectroscopic studies, NBO analysis and thermodynamic functions based on density functional theory

• Geometrical parameters of αBpTN obtained by B3LYP/6-31+G(d) and B3LYP/6-311++G(d) method.
• The infrared and Raman spectra were also predicted from the calculated intensities.
• Theoretical spectra were interpreted with the aid of normal coordinate analysis.
• Density plot of HOMO–LUMO energy surface were plotted to identify the donor and acceptor.
• The variation of dipole moment, polarizability is only in the intramolecular charge transfer of the αBpTN.

In this work, the experimental and theoretical study on molecular structure and vibrational spectra of α-bromo-p-tolunitrile (αBpTN) are studied. The energies of possible conformers obtained from DFT theory with 6-31+G(d) and 6-311++G(d) basis sets identified the most stable conformer of αBpTN as C2 conformer. The differences between the observed and scaled wavenumber values of most of the fundamentals are very small in B3LYP/6-311++G(d) than B3LYP/6-31+G(d). The first hyperpolarizability (β0) of this novel molecular system and related properties (β and μ) of αBpTN are calculated using B3LYP/6-31+G(d) and B3LYP/6-311++G(d) method on the finite-field approach. Stability of the molecule arising from hyperconjugative interactions, charge delocalization have been analyzed using natural bond orbital analysis. The results show that charge in electron density (ED) in the σ* and π* antibonding orbital and second order delocalization energies conforms the occurrence of intramolecular charge transfer within the molecule. The calculated HOMO and LUMO energies show that charge transfer occurs in the molecule. Finally the vibrations of CN and CH2Br groups coupled with skeletal vibrations are also investigated.