Vinylogy the α-carbon immediately adjacent to the carbonyl, as would a simple enolate. Allylic electrophiles often react by vinylogous attack of a nucleophile rather than direct addition. A further example of vinylogous reactivity: ascorbic acid (Vitamin C) behaves as a vinylogous carboxylic acid by involvement of its carbonyl moiety, a vinyl group within the ring, and the lone pair on the hydroxyl group acting as the conjugated system. Acidity of the hydroxyl proton at the terminus of the vinyl group in ascorbic acid is more comparable to a typical carboxylic acid than an alcohol because two major resonance structures stabilize the
Folinic acid to be metabolized in the liver before it could support growth of "L. citrovorum." The synthesis of citrovorum factor by liver cells in culture was eventually accomplished from pteroylglutamic acid in the presence of suitable concentrations of ascorbic acid. The simultaneous addition of sodium formate to such systems resulted in increased citrovorum factor activity in the cell-free supernatants (producing, as now known, the 5-formyl derivative), and from this method of preparation of large amounts of the factor, its structure as levo-folinic acid (5-formyl tetrahydrofolic acid) was eventually deduced. Folinic acid should be distinguished from folic acid (vitamin B). However, folinic