Lone-Pair Orientation Effect of an α-Oxygen Atom on (1)JCC NMR Spin-Spin Coupling Constants in o-Substituted Phenols. Experimental and DFT Study

Oscar E Taurian; Rubén H Contreras; Dora G De Kowalewski; Jorge E Pérez; Cláudio F Tormena

doi:10.1021/ct7000396

Lone-Pair Orientation Effect of an α-Oxygen Atom on (1)JCC NMR Spin-Spin Coupling Constants in o-Substituted Phenols. Experimental and DFT Study

J Chem Theory Comput. 2007 Jul;3(4):1284-94. doi: 10.1021/ct7000396.

Authors

Oscar E Taurian¹, Rubén H Contreras¹, Dora G De Kowalewski¹, Jorge E Pérez¹, Cláudio F Tormena¹

Affiliation

¹ Department of Physics, FCEFQyN, National University of Río Cuarto, Ruta Nacional No. 36, Km 601, 5800 Río Cuarto, Argentina, Physical Chemistry Section, School of Chemistry, Biochemistry and Pharmacy, National University of San Luis, Chacabuco and Pedernera, 5700 San Luis, Argentina, Department of Physics, FCEyN, University of Buenos Aires and CONICET, Ciudad Universitaria, Pab. 1, (C1428EHA) Buenos Aires, Argentina, and Chemistry Institute, State University of Campinas, CP 6154, CEP: 13084-971, Campinas, SP, Brazil.

PMID: 26633202
DOI: 10.1021/ct7000396

Abstract

The well-known N lone-pair orientation effect on (1)JCC spin-spin coupling constants (SSCCs) in oximes and their derivatives was used to study how negative hyperconjugative interactions of type LP1(O) → σ*CC depend on ortho interactions involving the OH group. This study demanded the following analyses: (i) a qualitative estimation of how (1)JCC SSCCs are affected by hyperconjugative interactions, (ii) a study of similar stereochemical effects to those in oximes, but in (1)JC1C2 and (1)JC1C6in a series of 2-substituted phenols, and (iii) a quantitative estimation, with the natural bond order approach, of some key electron delocalization interactions. A few unexpected results are quoted. LP1(O) → σ*CC interactions are affected by proximity interactions as follows: (a) they are enhanced by hydrogen bonds transferring charge into the (O-H)* antibonding orbital; (b) they are enhanced by proximity interactions of type LP1(O)···H-C; (c) they are inhibited by interactions of type LP(O1)···H-O. Consequences of these observations are discussed.