H-Bonding-Assisted Substituent Effect

In this paper we investigate the influence of intramolecular noncovalent interaction, i.e., H-bonding and Li-bonding, on the properties of substituents communicating through the resonance (mesomeric) effect in such molecular systems as salicylaldehyde, o-hydroxy Schiff base, o-nitrosophenol, and their lithium analogues. The investigated systems are usually considered as molecular patterns of intramolecular resonance-assisted hydrogen bonds (or its analogues in the case of Li-bonded systems). We show that the relation between intramolecular noncovalent interactions, A−H···B and A−Li···B, and the π-electron delocalization in the sequence of π-conjugated covalent bonds linking A and B can be considered in terms of the Hammett-like substituent effect in which electron-donating and electron-withdrawing properties of substituents are affected by the noncovalent interaction.