Unveiling the structural and energetic properties of thiazole-water complex by microwave spectroscopy and theoretical calculations

Microwave spectra, molecular geometries, and internal rotation of CH3 in N-methylimidazole⋯H2O and 2-methylimidazole⋯H2O Complexes

“…In general, contributions of in-plane vibrations to Δ 0 are negative whereas out-of-plane vibrations make positive contributions. The magnitudes of changes in Δ 0 on addition of H 2 O to each of imidazole, 4 thiazole 6 and isoxazole 7 are −0.02, −0.05 and +0.2 u Å 2 respectively which are broadly consistent with the observations of the present work. In striking contrast, the change in Δ 0 when attaching H 2 O to pyridine 36 has been observed to be greater than 8 u Å 2 .…”

“…Melandri et al , McGlone et al , Caminati et al , McKenzie et al and Li et al identified non-linear hydrogen bonds in pyrimidine⋯H 2 O, 8 isoxazole⋯H 2 O, 7 pyridazine⋯H 2 O, 41 pyrazine⋯H 2 O, 42 pyridine⋯H 2 O 36 and thiazole⋯H 2 O 6 respectively. Our group recently reported that imid⋯H 2 O 4 contains a non-linear hydrogen bond where ∠(O–H b ⋯N3) = 172.1(26)° in the r 0 geometry.…”

Characterization of Large-Amplitude Motions and Hydrogen Bonding Interactions in the Thiophene–Water Complex by Rotational Spectroscopy

“…Based on the quantum mechanical calculations from Table 1, conformer I is predicted to be the global minimum geometry for the complex and appears to be stabilized by O−H interactions in which one hydrogen of water binds to the πorbital of a CC bond, while the other hydrogen atom is directed above the middle of the ring (Figure 1). This is contrary to the most stable conformer reported for the monohydrates of furan 8 and pyridine (N•••H−O) 5 where the center of mass of water lies in the plane of the ring such that water binds to the most electronegative heteroatom or with the hydrogen attached to it in the case of pyrrole. The structure reported to be the most abundant based on the Ar matrix IR spectrum, 10 forming a C−H•••O HB (conformer II in this work), is predicted to be at least 2.4 kJ mol −1 (Table 1) less stable than conformer I at the B2PLYP-D3(BJ)/def2-TZVP level.…”

“…6 The scenario is more complicated for aromatic heterocycles as additional contacts may be established with the heteroatom. [3][4][5]7,8 The presence of multiple potential binding sites with interaction energies that are often sensitive to the computational levels chosen affirms the importance of experimental studies of isolated solvent− solute complexes.…”

“…Coupled with the complexity described above, rotational spectroscopic studies of the monohydrated complexes of pyrrole (pyrrole−w), 4,9 pyridine (pyridine−w), 5 and thiazole (thiazole−w) 8 revealed that due to a shallow potential energy surface around the global minimum geometry, the ground-state structures of these complexes, stabilized by N−H•••O (pyrrole−w) and N•••H−O (pyridine−w and thiazole−w) hydrogen bonds (HBs) in which the oxygen atom of water lies in the same plane as the heterocyclic structure, are highly influenced by large-amplitude motions. These motions (not typically captured by routine computational methods) are associated with the internal dynamics of water and may lead to tunneling splittings in the rotational spectrum depending on the barrier height.…”