Synthesis, structural and conformational analysis of a 3 × 3 isomer grid based on nine methyl-N-(pyridyl)benzamides

Abstract

A 3 × 3 isomer grid of nine methyl-N-(pyridyl)benzamides (C₁₃H₁₂N₂O) as Mxx (x = para-/meta-/ortho-) has been synthesized and characterised to evaluate and correlate structural relationships from both ab initio calculations (gas-phase, PCM-SMD model solvated forms) and the solid-state. The effect of methyl group (Mx) and pyridine N atom (x) substitution patterns on molecular conformations from calculations and in terms of molecular organisation is evaluated. The primary hydrogen bonding is _amideN–H⋯N_pyridine in eight isomers but is _amideN–H⋯OC_amide in Mpm. The N–H⋯N interactions form C(6) chains in the Mxp series, C(5) chains in Mmm, Mom and cyclic centrosymmetric R²₂(8) rings in the Mxo series. Of note is the short intradimer C–H⋯π(arene) interaction in Moo, one of the shortest reported in a neutral organic system C⋯Cg = 3.3875(18) Å, H⋯Cg = 2.46 Å [2.33 Å] and C–H⋯Cg = 167° [166°] [with normalised C–H distances]. Conformational features and differences between the computational calculations and crystal structures are discussed.