Experimental and theoretical investigations of spectroscopic properties of N-acetyl-5-methoxytryptamine

Ab initio and density functional computations of the vibrational (IR) spectrum, molecular geometry, the atomic charges and molecular polarizabilities were carried out on melatonin. The FTIR spectrum of melatonin is recorded in solid phase. Assignments were made in accordance with the calculated and experimental spectra. The UV spectrum was measured in methanol. In order to gain some insight into the recorded spectrum, the quantum mechanical calculations were performed for melatonin using both ZINDO/CIS and TD DFT with B3LYP/6-31G* basis set. In addition, isotropic H-1- and C-13-nuclear magnetic shielding constants of this compound were calculated by employing the direct implementation of the gauge including-atomic-orbital (GIAO) method at the B3LYP density functional theory using 6-311G basis set. Theoretical values are compared to the experimental data.