Spectroscopic Characterization, Hirshfeld Surface, DFT, and TD-DFT of tert-Butyl Phenethylcarbamate and 1,1-Dimethyl-3-Phenethylurea

Tert-butylphenethylcarbamate (1) and 1,1-dimethyl-3-phenethylurea (2) were synthesized, and their structures were confi rmed by NMR, FTIR, and mass spectrometry techniques. The experimental spectroscopic data of 1 and 2 were compared with the corresponding calculated ones obtained by density functional theory (DFT) and time-dependent DFT methods, for which the hybrid functionals B3LYP, B3P86, and PBE0 combined with the 6-311++G(d,p) basis set were tested. The solvent effect was considered using the implicit model — integral equation formalism-polarizable continuum model (IEFPCM). Relatively good correlation (R² > 90%) was obtained between the experimental and predicted spectral data. The conformational effect on the absorption maximum λ_max was negligible, that is, λ_max of different conformers varied by less than 0.01 nm. Hirshfeld surface analysis and electrostatic potential calculations of the closest intermolecular contacts between active atoms of 1 and 2 revealed that the closest interactions were between hydrogen atoms of 39.6 and 46.3%, respectively.