Conformation of the ascorbic acids in aqueous solution

Abstract The complete analysis of the H-1 and C-13 NMR spectra of L-ascorbic acid 1 and D-araboascorbic acid 2 has been carried out for acidic aqueous solutions. Conformational equilibrium of the side chain kof 1 and 2 was determined from the vicinal HH and Cz.sbnd;H couplings. The obrained results are compared with previous models and with those provided by molecular mechanics calculations. Assuming a constant J(C,H)/J(H,H) ratio of 0.58 between equivalent vicinal CH and HH couplings the two methylene protons were assigned and the generalized Karplus equation was applied to the CH couplings.