An ab initio study of the H2O-mediated 1,3-hydrogen rearrangement in the isoelectric series: X, Y = CH2, NH, or O

1991 ◽  
Vol 69 (10) ◽  
pp. 1589-1599 ◽  
Author(s):  
Raymond A. Poirier ◽  
Dake Yu ◽  
Peter R. Surjan
Keyword(s):  
Ab Initio ◽  
Solvent Effects ◽  
Basis Set ◽  
Correlation Effects ◽  
Ab Initio Study ◽  
Reaction Field ◽  
Effect Of Solvent ◽  
Isoelectronic Series ◽  
Intramolecular Hydrogen ◽  
Hydrogen Rearrangement

Ab initio calculations are performed to investigate the effect of water on the 1,3-intramolecular hydrogen rearrangement in the [Formula: see text] isoelectronic series, for X, Y = CH2, NH or O, by modeling with a single H2O molecule. The geometries for the complexes are optimized at both the 3-21G and 6-31G** basis set levels. MP2 and some MP4 calculations are performed to take into account the correlation effects, and ZPV corrections are calculated at the MNDO level. The results show that the water molecule has a significant effect on the molecules in which hydrogen bonds can be formed or partially formed. The "solvent effects" are also examined using the self-consistent reaction-field (SCRF) approach. A combination of supermolecule and SCRF approach appears to work well at predicting the effect of solvent on relative stabilities and barriers. Key words: tautomerism, ab initio, 1,3-hydrogen rearrangement, solvent effects.

The Structure of N-Acetylprolinamide in the Solid State and in the Gasphase. A Remarkable Lattice Effect as the Result of a Competition Between Inter-and Intramolecular Hydrogen Bonds of Different Strengths

1998 ◽  
Vol 53 (1-2) ◽  
pp. 61-66 ◽  
Author(s):  
Gerhard Raabe ◽  
Axel Sudeikat ◽  
Robert W. Woody
Keyword(s):  
Solid State ◽  
Ab Initio ◽  
Conformational Changes ◽  
Molecular Conformation ◽  
Carbonyl Oxygen ◽  
Basis Set ◽  
Am1 Method ◽  
Lattice Effect ◽  
The One ◽  
Intramolecular Hydrogen

Abstract In the solid state, the conformation of N-actetylprolinamide is stabilized by two intermolecular O···H bridges and one intramolecular N···H hydrogen bond. According to quantum chemical ab initio calculations with the 6-31+G* basis set at the one-determinant level, the intramolecular N ···H bond is not strong enough to maintain the solid-state molecular conformation the gas phase. The conformational changes predominantly consist in a rotation of the amide group about its C-C bond to the proline ring, resulting in a c/s-like conformation which is stabilized by a presumably stronger intramolecular O···H bond between one hydrogen atom of the NH2 group and the carbonyl oxygen of the acetyl subsituent bonded to the nitrogen atom of the five-membered ring. These confirmational changes cause a reduction of the molecular dipole moment by about 50%, indicating that the conformation in solution might be strongly solvent dependent. While both the MINDO/3 and the MNDO method in their standard parametrizations fail to reproduce the ab initio results, the lattice effect is reproduced at least qualitatively with the PM3 as well as with the AM1 method.

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