Resumen de Uv-vis, nmr and ft-ir spectra of tautomers of vitamin c. Experimental and dft calculations
Hussein A Dabbagh, Fatemeh Azami, Hussein Farrokhpour, Alireza Najafi Chermahini
Experimental and computational analysis of spectroscopic parameters of L-ascorbic acid (vitamin C) and its tautomers was investigated by Density Functional Theory (DFT) using B3LYP method. The optimized geometries and calculated vibrational frequencies were evaluated. The latter was compare with those of experimental values. The λmax values of L-ascorbic acid were found 259 (at pH = 3) experimentally, 238 and 247 nm calculated in the gas and water phase at TD-DFT methods, respectively. The experimental order of υ(Ο-Η) modes was obtained at υ(O3-Η3) > (O6-Ho6) > (O2-H2) > (O5-Ho5). The theoretical orders were calculated at υ(O6-Ho6) > (O2-H2) > (O5-Ho5) > (O3-H3) and υ(O3-H3) > (O5-Ho5) > (O6-Ho6) > (O2-H2), respectively, in the gas phase and aqueous phase. The highest wave number of tautomers (S,Z)-3,5,6-trihydroxy-2-oxohex-3-enoic acid (2), (2Z,4E)-2,3,5,6-tetrahydroxyhexa-2,4-dienoic acid (3), (R)-2-((S)-1,2-dihydroxyethyl)-4,5-dihydroxyfuran-3(2H)-one (4) was calculated for the stretching modes O6-Ho6, O3-H3, O6-Ho6 bonds, respectively, in the gas phase. The experimental and theoretical calculations of proton NMR predicted H3 as the most deshilded proton.
