Spectroscopic Characterization, Hirshfeld Surface, DFT, and TD-DFT of tert -Butyl Phenethylcarbamate and 1,1-Dimethyl-3-
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Journal of Applied Spectroscopy, Vol. 87, No. 4, September, 2020 (Russian Original Vol. 87, No. 4, July–August, 2020)
SPECTROSCOPIC CHARACTERIZATION, HIRSHFELD SURFACE, DFT, AND TD-DFT OF tert-BUTYL PHENETHYLCARBAMATE AND 1,1-DIMETHYL-3-PHENETHYLUREA M. B. Alshammari,a* E. H. Anouar,a and G. A. El-Hitib
UDC 539.143.43
Tert-butylphenethylcarbamate (1) and 1,1-dimethyl-3-phenethylurea (2) were synthesized, and their structures were confirmed 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 λmax was negligible, that is, λmax 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. Keywords: time-dependent density functional theory, nuclear magnetic resonance, conformational analysis, tertbutylphenethylcarbamate, 1,1-dimethyl-3-phenethylurea. Introduction. Compounds containing both carbamate [1–3] and urea [4–6] moieties have always generated interest because they show a variety of biological activities. The most common methods of producing carbamate involve reactions between tert-butyloxycarbonyl benzotriazoles and amino acids [7], oxo-pyridazine and amines [8], di-tert-butyl dicarbonate and nitriles [9] or carboxylic acids [10], as well as chloroformates and nitro compounds [11]. Moreover, several efficient approaches for the synthesis of urea derivatives have been developed [12–14]. Aromatic carbamates and urea can be substituted efficiently by treatment with organolithium reagents followed by reactions with electrophiles [15–20]. Quantum chemical calculations are powerful tools for the confirmation of experimental 1H and 13C NMR chemical shifts [21–23] and UV-visible absorption bands [24–26]. The excited states may be calculated using different approaches [25–32]. Previous studies reported that B3LYP and PBE0 are appropriate hybrid functionals for the estimation of excited state energies [33–37]. Previously, we showed that B3P86 and B3LYP provide reliable estimates of the first excited state of a series of flavonoids and chalcones [38]. Lumpi et al. reported that M06-2X gave more accurate predictions of the absorption and emission spectra of oligothiophene-based compounds than PBE0 and B3LYP [39]. To predict the UV-visible spectra of pyranoanthocyanins, Quartarolo and Russo [28] performed time-dependent density functional
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