Structural analysis of 1-heptylamine by vibrational spectroscopy and density functional theory

FT-IR and Raman spectra of 1-heptylamine (1-ha) have been recorded in the region of 4000-10 cm-1 and 4000-50 cm-1, respectively. The conformational analysis, optimized geometric parameters (bond lengths, bond and dihedral angles), normal mode frequencies and corresponding vibrational assignments of 1-ha (C7H17N) were theoretically examined by means of the density functional theory (DFT) together with the B3LYP functional and 6-31++G(d,p) basis set. Furthermore, reliable vibrational assignments have been made on the basis of potential energy distribution (PED) and some thermodynamics functions, highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO) of 1-ha were predicted. Calculations were carried out with the possible ten conformational isomers (TT, TG, GT, GT1, GG1, GG2, GG3, GG4, GG5, GG6; T and G denote trans and gauge) of 1-ha, both gas phase and solution. Solvent effect was investigated by apolar benzene and polar methanol. All results indicate that the B3LYP functional provides satisfactory evidence for the prediction of vibrational frequencies and the TT isomer is the most stable form of 1-ha in all medium.