Geometry, vibrations and torsional potential of 1-phenyl naphthalene: A combined ab-initio and experimental study

Abstract

The torsional potential, conformations and transition state (TS) of 1-phenylnaphthalene (1PN) in S0 are computed through density functional theory (DFT), Hartree- Fock (HF) and MP2 methods. The global minimum shows the two rings are oriented at 580 ± 40. Discrepancies are observed in the HF method, consistent with earlier observations. The torsional potential energy curve (PEC) starts to deviate from its periodic form as the rings approach towards planarity. The necessary corrections to the torsional potential are discussed and a potential energy surface (PES) is drawn. The phenyl torsion in 1PN are compared with some analogous molecules in detail. IRC calculations identify the transition region and show the pathway from TS to the global minimum. Experimentally observed FT-IR and Raman spectra corroborate well with the computed ones. The low-frequency torsional motion appears at 48 cm−1 in Raman spectrum. Benzene and naphthalene ring modes are identified and assigned. HOMO and LUMO show the electronic excitation predominantly is π→π* in nature. Maximum hardness principle and minimum electrophilicity principles are discussed here. Electrostatic potential surface identifies the regions where intermolecular interactions will be the strongest.