Chemistry of amidines. Part 2. Substituent and solvent effects on rotational barriers in N′-pyridylformamidines

Abstract

Values of ΔG^‡ for rotation about the carbon–dimethylamino bond in a range of substituted pyridyl formamidines have been determined by ¹H NMR spectroscopy in a small range of solvents. The correlation of ΔG^‡ with σ^– is interpreted in terms of a coplanar amidine and pyridine system. The variation of ΔG^‡ with solvent is interpreted in terms of hydrogen bonding to the amino lone pair of the amidine.