Vibrational spectroscopic investigation and conformational analysis of 1-heptylamine: A comparative density functional study

• Infrared, Raman and quantum chemical calculations of 1-ha.
• The TT isomer is supposed to be the most stable form of 1-ha.
• Conformational energy barriers are low and independent of the solvent.
• Vibrational frequencies and intensities change when going from non-polar to polar solvents.

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, normal mode frequencies and corresponding vibrational assignments of 1-ha (C7H17N) have been examined by means of the Becke-3-Lee-Yang-Parr (B3LYP) density functional theory (DFT) method together with the 6-31++G(d,p) basis set. Furthermore, reliable vibrational assignments have been made on the basis of potential energy distribution (PED) and the thermodynamics functions, highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO) of 1-ha have been predicted. Calculations have been 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 in gas phase and in solution. Solvent effects have theoretically been investigated using benzene and methanol. All results indicate that the B3LYP method provides satisfactory evidence for the prediction of vibrational frequencies and the TT isomer is the most stable form of 1-ha.

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