Phenyl groups, analytical determination

Acetylation.— Acetylation of n-arabino- and n-li/xo-hexulose phenyl-osazones results in the formation of crystalline tetraacetates. Wolfrom and coworkers have established an analytical technique that differentiates between iV-acetyl and 0-acetyl groups the latter were determined by the procedure of Kunz and Hudson. They were thus able to show that all four acetyl groups are 0-acetyl groups. This discovery eliminated the possibility of cyclic structures, which would have required three 0-acetyl groups and one A-acetyl group. The infrared spectra of osazone acetates also support the acyclic structure, as these compounds show only one carbonyl band, namely, that of the 0-acetyl groups. 

Analytical protocols based on H- C HSQC NMR spectroscopy [40] and UV-Vis-spectroscopy [41] were developed to rapidly determine the rruxture composition. Comparison of the relative hydrazone concentrations in both Ubraries revealed the strongest amplification for hydrazone 43 equipped with an ammonium group. Positioning of that ammonium close to the ester moiety in functionalized phenyl acetate 44 indeed resulted in an enhanced cleavage rate. A series of control experiments supported the hypothesis that this was indeed due to transition state stabUization. 

---