Structure of the symmetric monooxime of 1,2,3-indantrione in gas, solution and solid states

Different hydrogen-bonding modes in two closely related oximes

Two closely related oximes, namely 1-chloroacetyl-3-ethyl-2,6-diphenylpiperidin-4-one oxime, C(21)H(23)ClN(2)O(2), (I), and 1-chloroacetyl-2,6-diphenyl-3-(propan-2-yl)piperidin-4-one oxime, C(22)H(25)ClN(2)O(2), (II), despite their identical sets of hydrogen-bond donors and acceptors, display basically different hydrogen-bonding patterns in their crystal structures. While the molecules of (I) are organized into typical centrosymmetric dimers, created by oxime-oxime O-H...N hydrogen bonds, in the structure of (II) there are infinite chains of molecules connected by O-H...O hydrogen bonds, in which the carbonyl O atom from the chloroacetyl group acts as the hydrogen-bond acceptor. Despite the differences in the hydrogen-bond schemes, the -OH groups are always in typical anti positions (C-N-O-H torsion angles of ca 180 degrees ). The oxime group in (I) is disordered, with the hydroxy groups occupying two distinct positions and C-C-N-O torsion angles of approximately 0 and 180 degrees for the two alternatives. This disorder, even though the site-occupancy factor of the less occupied position is as low as ca 0.06, is also observed at lower temperatures, which seems to favour the statistical and not the dynamic nature of this phenomenon.

Intramolecular hydrogen-bonding interactions in 2-nitrosophenol and nitrosonaphthols: ab initio, density functional, and nuclear magnetic resonance theoretical study

Intramolecular hydrogen bonding (IHB) interactions and molecular structures of 2-nitrosophenol, nitrosonaphthols, and their quinone-monooxime tautomers were investigated at ab initio and density functional theory (DFT) levels. The geometry optimization of the structures studied was performed without any geometrical restrictions. Possible conformations with different types of the IHB of the tautomers were considered to understand the nature of the HB among these conformers. The effect of solvent on hydrogen bond energies, conformational equilibria, and tautomerism in aqueous solution were studied. Natural bond orbital analysis was performed to study the IHB in the gaseous phase and in aqueous medium. The NMR 1H, 13C, 15N, and 17O chemical shifts in the gaseous phase and in solution for the studied compounds were calculated using the gauge-including atomic orbitals approach implemented in the Gaussian 03 program package. The optimized geometrical parameters and 1H NMR chemical shifts are in good agreement with previous theoretical and experimental data.