Conformation and bonding of 2-methoxypyridine and its monohydrate from rotational spectra

Rotational spectra of 2-methoxypyridine and its monohydrate have been characterized by pulsed jet Fourier transform microwave spectroscopy and complementary ab initio calculations. Rotational spectra of the parent monomer and seven mono-substituted isotopologues (¹³C and ¹⁵N) were measured in natural abundance, which allow determining the accurate structure of the skeleton of 2-methyoxypyridine. The barrier to the methyl internal rotation was determined from the A/E torsional symmetry species of the rotational transitions. For the 2-methyoxypyridine⋯H₂O complex, rotational spectra of the parent dimer and isotopologues formed with isotopically enriched water (H₂ ¹⁸O, HOD, DOH and D₂O) indicate that the observed isomer is stabilized by a strong O[sbnd]H⋯N and a secondary bifurcated (C[sbnd]H)₂⋯O weak hydrogen bonds. Bader's quantum theory of atoms in molecules and Johnson's non-covalent interaction analyses were applied and visualized to have a better understanding of the non-covalent interactions in 2-methyoxypyridine⋯H₂O.