The First Phenyl-N-pyridinylcarbamate Structures: Structural and Conformational Analysis of Nine Methoxyphenyl-N-pyridinylcarbamates

A 3 X 3 isomer grid of nine methoxyphenyl-N-pyridinylcarbamates (C13H12N2O3) as CxxOMe (x = para-/meta-/ortho-) represents the first phenyl-N-pyridinylcarbamate crystal structures to be reported. Structural relationships have been correlated in all nine crystal structures as derived from ab initio calculations and the solid-state using conformational analysis. N-H center dot center dot center dot N hydrogen bonds dominate as the primary interaction in all nine isomers. Two isomers (CmmOMe, CmoOMe) form unusual cyclic N-H center dot center dot center dot N trimer synthons as R-3(3)(15) with two distinct conformations isolated in the CmoOMe structure, whereas the three CoxOMe isomers form N-H center dot center dot center dot N hydrogen bonded dimers based on the R-2(2)(8) motif. For all isomers, C-H center dot center dot center dot O interactions assist in aggregation, and in most cases the methoxy group augments the hydrogen bonding. The solid state and modeled conformations are mismatched in three isomers where the methoxy groups and meta-methoxyphenyl rings (mOMe) (in the solid state) adopt metastable or unstable conformations compared to their optimized computational models. This is rationalized in terms of preferred solid state conformations and observed interactions as compared to the computational models.