amide-iminol tautomerism was studied for ionized oxamic acid (oa+•) in the gas phase using thedft method with the ub3lyp functional and various basis sets {6-31++g(d,p), 6-311+g(d,p), and augcc-pvdz}. among twenty tautomers-rotamers possible for oa+•, eleven isomers were found to bethermodynamically stable. similarly as for the neutral molecule, ionization (oa → oa+• + e) favors theamidization ...

the concept of resonance assisted hydrogen bond (rahb), which usually occurs in b diketons, has a remarkable role in chemistry. these molecules, which contain heteroatom particularly o and n, are species with biological interest in protein folding and dna pairing. therefore, the amplification of hydrogen bonds strength by substituents may be important in life sciences. in the current research, ...

An n→π* interaction stems from the delocalization of the electron pair (n) of a donor group into the antibonding orbital (π*) of a carbonyl group. Crystallographic analyses of five pairs of diastereoisomers demonstrate that an n→π* interaction can induce chirality in an otherwise planar, prochiral carbonyl group. Thus, a subtle delocalization of electrons can have stereochemical consequences.

The HOMA (Harmonic Oscillator Model of Aromaticity) index, reformulated in 1993, has been very often applied to describe π-electron delocalization for monoand polycyclic π-electron systems. However, different measures of π-electron delocalization were employed for the CC, CX, and XY bonds, and this index seems to be inappropriate for compounds containing heteroatoms. In order to describe proper...

The HOMA (Harmonic Oscillator Model of Aromaticity) index, reformulated in 1993, has been very often applied to describe π-electron delocalization for monoand polycyclic π-electron systems. However, different measures of π-electron delocalization were employed for the CC, CX, and XY bonds, and this index seems to be inappropriate for compounds containing heteroatoms. In order to describe proper...

Ni( ii ) π-back bonds with CO of flavonolate (fla − and enolate fla σ-bonds synergistically. π-Delocalization in activates it to release CO.

Carbonyl-carbonyl (C=O···C'=O') interactions are ubiquitous in both small and large molecular systems. This interaction involves delocalization of a lone pair (n) of a donor oxygen into the antibonding orbital (π*) of an acceptor carbonyl group. Analyses of high-resolution protein structures suggest that these carbonyl-carbonyl interactions prefer to occur in pairs, that is, one donor per accep...

Amide-iminol tautomerism was studied for ionized oxamic acid (OA+•) in the gas phase using theDFT method with the UB3LYP functional and various basis sets {6-31++G(d,p), 6-311+G(d,p), and augcc-pVDZ}. Among twenty tautomers-rotamers possible for OA+•, eleven isomers were found to bethermodynamically stable. Similarly as for the neutral molecule, ionization (OA → OA+• + e) favors theamidization ...

7 ABSTRACT: Vibrational frequencies can be measured and calculated with 8 high precision. Therefore, they are excellent tools for analyzing the electronic 9 structure of a molecule. In this connection, the properties of the local 10 vibrational modes of a molecule are best suited. A new procedure is described, 11 which utilizes local CC stretching force constants to derive an aromaticity 12 ind...

Novel DNA base pair derivatives (A2CunU, A2CunC, G3CunU, and G3CunC) are designed by aromatic expansion of pyrimidine bases with four kinds of hetero-rings (denoted by nC and nU, n = 1, 2, 3, and 4) and metal-decoration through Cu replacement of hydrogens in the Watson-Crick hydrogen bond region. Their structures and properties are calculated for examining the cooperative effects of the two mod...