Long range transmission of polar effects in cholinergic 3-arylideneanabaseines. Conformations calculated by molecular modelling

Benzylidene products resulting from acid-catalyzed aldol condensations of aryl aldehydes and anabaseine at position 3 of the tetrahydropyridine ring have E stereochemistry. In spite of a chemical shift scale ranging only over 0.11 ppm the methylene protons (H-6) adjacent to the imino group of the tetrahydropyridine ring show an excellent Hammett correlation using σ_M and σ_P values. Methoxy and chloro groups in an ortho position require a σ₁, parameter. Substrates with one or two ortho methyl groups deviate. AM1 and MM2 calculations indicate that both the phenyl and pyridyl rings are twisted out of a common plane defined by the central ring.