Theoretical and experimental 1H-NMR spectroscopy for a series of Cbz-amino acids, dissolved in DMSO, at constant temperature and pressure

Abstract

In this work, experimental and theoretical ¹H-NMR (¹H Nuclear Magnetic Resonance) spectroscopy was performed for Cbz-glycine, Cbz-alanine, Cbz-valine, and Cbz-phenylalanine, dissolved in dimethyl sulfoxide, at 298.15 K and 1 bar. The data extracted from the calculations showed that for the most stable conformer in each part, the energy (E), total Gibbs free energy (G_tot), and rigid rotor harmonic oscillator (RRHO) have an exponential relationship with molecular weight (M_w) of the studied Cbz-AA. ANMR (Anisotropic Nuclear Magnetic Resonance) output file was used to draw theoretical ¹H-NMR spectra. ¹H-NMR spectra and key parameters (chemical shifts, δ, and integration) were theoretically calculated and experimentally obtained for the studied systems. The objective of this work is to study the molecular structures of Cbz-AAs. The obtained chemical shifts were used to identify functional groups in the Cbz-AAs, including alkyls (-CH₂, -CH₃, and –CH[CH₃]₂), amide (-NHCO), and phenyl groups. Density functional theory (DFT) was employed for our ¹H-NMR calculations using the def2-TZVPP (triple-zeta valence polarized basis) and def2-TZVP (triple-zeta valence polarized basis) basis sets. The experimental ¹H^-NMR spectra were obtained using a 600 MHz NMR spectrometer. The results show a good agreement in the chemical shifts and integration between the calculated and experimental ¹H-NMR spectra.

KEY WORDS: Chemical shift, ¹H-NMR, DFT, def2-TZVPP, def2-TZVP, Cbz-AA, Spectra, ANMR

Bull. Chem. Soc. Ethiop. 2026, 40(3), 485-500.                                                 

DOI: https://dx.doi.org/10.4314/bcse.v40i3.1