Structure-retention relationships in the gas chromatography of N,N-dialkylhydrazones

N,N-Dialkylhydrazones [DAHs; R(1)R(2)C = N-1-N-2(R(3))(2)] were prepared and their Kovats retention indices determined on 100% dimethylpolysiloxane (HP-1) and 5% diphenyl and 95% dimethylpolysiloxane (HP-5) stationary phases. The physico-chemical and retention behaviour of the DAHs depend greatly on whether R(2) = H or an alkyl group. A similar difference is observed in the alkane and oxo homomorphic factors of DAHs formed from aldehydes or ketones. The difference is explained on the basis of NMR and quantum-chemical results by intramolecular interactions between R(2) and the lone pair of the N-2 atom. A single linear equation is suitable for prediction of retention indices if parameters are introduced representing resonance structure (bond angle and electron density) besides I-oxo, or the van der Waals' surface.