Proton affinities in monosubstituted benzenes

Theoretical absolute proton affinities obtained for monosubstituted benzenes C H X are presented in Table 1. The examined substituents encompass X = C//3, OH, OGH3, 

Another very important facet of theoretical considerations is interpretation of the phenomena under study. This is accomplished by quantum mechanical models, which yield simplified but quintessential picture of the molecular behavior [32]. In order to rationalize ortho-para directional ability of OH group let us make an inspection of the valence bond (VB) resonance structure of the benzenium ion (Fig.2). It appears that a depletion 

Obviously, combined effect of the OH substituent and the proton meta attack is counteractive resulting in a less stable conjugated acid. An instructive case is provided by anisole (3) since it sheds light on the role of the alkyl group within alkoxy substituent. Perusal of data presented in Table 1 reveals that protonation at the ring positions in (3) is energetically more favorable by 3 — 5 kcal/mol relative to phenol. This feature is 

Proton Affinities in Polysubstituted Benzenes-The Additivity Rule 2.4.1. Increments 

Before proceeding further we introduce increments which describe a change in the aromatic ring proton affinities in monosubstituted benzenes. This is most conveniently done by using homodesmic reactions [35]. In this type of hypothetical reaction the number of atoms of the same element, specific types of covalent bonds and approximate hybridization states are preserved being equal in reactants and products. This is very important since it 

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