Influence of the Structure of Ketones and Acidity of Phenols Upon Their Complexation Processes. Part 2. n‐ vs. π‐Complex Competition Depending on Ketone Branching and Phenol Acidity.

Abstract For phenol-alkylketone associations, lineshape analysis of the associated ν OH band allows for the separation of two different complexes attributed either to π or n (lone-pair) carbonyl electrons. Using an original methodology, individual constants K n and K π have been evaluated and their evolution according to the structure of the two partners (ketone and phenol) characterized by a factor analysis treatment. For n -complexes, reduced ketone characteristics K nc are proportional to the number of branches alpha to the carbonyl, K π being insensitive to the structure of the ketone. Both K n and K π are linearly related to the phenol acidity, but with different sensitivities. This induces striking differences in the relative weight of the n - and π-complexes depending on the ketone-phenol pair investigated. For ortho -halogenophenols, the influence of intramolecular hydrogen bonding is discussed.