ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Effect of the substituents upon the acid-base properties of benzophenone derivatives

O. Kyseľ and I. Jány

Polymer Institute, Slovak Academy of Sciences, 809 34 Bratislava

Abstract:  It has been found that the protonation equilibrium constants of 2-hydroxy-5-methylbenzophenone m- and p -substituted on the phenyl group can be correlated with the σ⁺ constants according to the equation pK_b = — 6.18 — 0.96 < σ⁺. The correlation between the protonation equilibrium constants of m- and p-substituted benzophenone and o+ constants obeys the equation pKb = -6.39-1.40 σ⁺. The difference in the basicity of 2-hydroxy-5-methylbenzophenone derivatives compared to benzophenone and 2-hydroxybenzophenone substituted on the 2-hydroxyphenyl group is explained by a twisted position of the phenyl group as a result of the repulsion of о-hydrogen atoms on this and 2-hydroxyphenyl group. Based on the рK_b measurements of the different types of aromatic ketones it has been established that an intramolecular hydrogen bond significantly decreases the basicity of the carbonyl group and compensates the resonance effect of the o-hydroxyl group. It has been found that, depending on the type of the ketone, the correlation between рK_b and v^-(C = 0) of different types of ketone falls apart to give individual linear branches. The v^-(C = 0) values of different types of ketone correlate well with the jr-electron bond order of the carbonyl group.

Full paper in Portable Document Format: 281a70.pdf

Chemical Papers 28 (1) 70–76 (1974)