This paper reports the synthesis of a series of piperidones 1-8 by the Mannich reaction and analysis of their structures and conformations in solution by NMR and mass spectrometry. The six-membered rings in 2,4,6,8-tetraphenyl-3,7-diazabicyclo[3.3.1]nonan-9-ones, compounds 1 and 2, adopt a chair-boat conformation, while those in 2,4-diphenyl-3-azabicyclo[3.3.1]nonan-9-ones, compounds 3-8, adopt...

Density functional theory methods(DFT) and natural bond orbital (NBO) analysis were used to investigate the effects of isomerism and side chain mutation at a microscopic level on the stability, binding energy and NMR/NQR tensors of structural isomers, L- methionylasparagine (Met-Asn) and L- asparagylmethionine (Asn-Met) in the gas phase. The results represented that the isomerism and side chain...

Cooperative effects in two-dimensional cyclic networks containing intermolecular three-centered hydrogen bonding interactions of the type H1...A...H2 are investigated by means of ab intio molecular orbital and density functional theory calculations. Ring-like clusters consisting of three and up to nine monomers of the cis-cis isomer of carbonic acid H2CO3 are used as basic models, where each un...

In the present work, the substituent effect on the strength of H-bonds in the guanine – cytosine base pair was studied when the substituents are connected to the guanine base through a phenyl ring. In this study, guanine was substituted in the H8 and H9 positions by electron donating (ED) and electron withdrawing (EW) groups mediated by a phenyl ring in the gas phase. The calculations were perf...

Vibrational analysis of the 2,6-bis(p-methyl benzylidene cyclohexanone) [PMBC] compound was carried out by using NIR FT-Raman and FT-IR spectroscopic techniques. The equilibrium geometry, various bonding features and harmonic vibrational frequencies of PMBC have been investigated with the help of B3LYP/6-31 G(d) density functional theory method. The optimized geometry clearly demonstrates cyclo...

Hydrogen bonds between backbone amides are common in folded proteins. Here, we show that an intimate interaction between backbone amides also arises from the delocalization of a lone pair of electrons (n) from an oxygen atom to the antibonding orbital (pi*) of the subsequent carbonyl group. Natural bond orbital analysis predicted significant n-->pi* interactions in certain regions of the Ramach...

Bioactive molecules are playing essential role in the field of drug discovery and various pharmaceutical applications. Vibrational spectral investigations of the anti-Candida agent ({[(1E)-3-(1H-imidazol-1-yl)-1-phenylpropylidene]amino}oxy)(4-methylphenyl)methanone ((1E)-IPMM) have been recorded and analyzed to understand its structural geometry, interand intra-molecular interactions. The equil...

The analysis of the electronic-structure changes along IRC paths for double-proton-transfer reactions in the formamide dimer (R1), formamide-thioformamide system (R2), and the thioformamide dimer (R3) was performed based on the extended-transition-state natural orbitals for chemical valence (ETS-NOCV) partitioning of the reaction force, considering the intra-fragments strain and the inter-fragm...

In this research at the first, xylometazoline hydrochloride drug (XY) and its fullerene connected form (FXY) were optimized. Natural Bond Orbital (NBO) calculations for these compounds were carried out at the B3LYP/6-31G* quantum chemistry level, in the gas phase and the liquid phase. These calculations can be performed at different accuracy levels depending on the aim of the theoretical study....