We experimentally and theoretically examined the conformation, pH, and temperature dependence of the CH2 stretching frequencies of glycine (gly) in solution and in the crystalline state. To separate the effects of the amine and carboxyl groups on the CH2 stretching frequencies we examined the Raman spectra of 2,2,2-d3-ethylamine (CD3-CH2-NH2) and 3,3,3-d3-propionic acid (CD3-CH2-COOH) in D2O. T...

Mixed dimers, trimers and tetramers composed of SO2 and CO2 molecules are examined by ab initio calculations to identify all minimum energy structures. While AIM formalism leads to the idea of a pair of C···O bonds in the most stable heterodimer, bound by some 2 kcal mol(-1), NBO analysis describes the bonding in terms of charge transfer from O lone pairs of SO2 to the CO π* antibonding orbital...

Sz~rnmnr~~ . From a molecular orbital study of model systems we derivc the electronic requiremcnts for the Grob fragmentation. The necessary condition for an allowed fragmentation in an ?I-C,-C,-C,-N system, or the amino cation +C,-C,-C,-N is the level ordering A below S . This in turn is set by maximal through-bond coupling of the empty cation orbital and the nitrogen lone pair. The conformati...

In the structure of the title compound, C(10)H(11)BrN(4), the plane of the substituted 1,2,3-triazole ring is tilted by 14.84 (10)° with respect to the mean plane of the pyridine ring. The pyridine and closest triazole N atoms adopt an anti arrangement which removes any lone pair-lone pair repulsions between the N atoms. This conformation is further stabilized by weak intermolecular C-H⋯N inter...

A high-resolution photoelectron spectrum of p-benzoquinone in the low energy ~9.5–11.5 eV! region is reported and analyzed with the aid of simulations based on high-level ab initio calculations. The results generally support the notion that the two prominent spectral features in this region are each due to a pair of final ion states. The lower energy feature beginning near 10 eV is due to oxyge...

Quantum chemical calculations have been carried out to study the electronic structure of metalated ylides particularly in comparison to their neutral analogues, the bisylides. A series of compounds of the general composition Ph3 P-C-L with L being either a neutral or an anionic ligand were analyzed and the impact of the nature of the substituent L and the total charge on the electronics and bon...

When PH(3) is paired with NH(3), the two molecules are oriented such that the P and N atoms face one another directly, without the intermediacy of a H atom. Quantum calculations indicate that this attraction is due in part to the transfer of electron density from the lone pair of the N atom to the σ(∗) antibond of a P-H covalent bond. Unlike a H-bond, the pertinent hydrogen is oriented about 18...

The N···S chalcogen bond between SF4 and a series of alkyl and arylamines is examined via ab initio calculations. This bond is a strong one, with a binding energy that varies from a minimum of 7 kcal/mol for NH3 to 14 kcal/mol for trimethylamine. Its strength derives in large measure from charge transfer from the N lone pair into the σ*(SF) antibonding orbitals involving the two equatorial F at...

The electron paramagnetic resonance of copper (II)-tetram m ine nitrate in solution of methanol and water has been investigated. The data obtained from the spectra at room tem perature and 97 °K together with the optical transition energies determined from single crystal polarized absorption spectra at 77 °K by other authors were used to calculate the LCAO-MO bonding parameters. The bonding orb...

The chemistry of 2-(1-pyrazolyl)- (2a) and 2-[1-(3,5-dimethylpyrazolyl]phenylnitrene (2b) has been studied in EtOH solution at room temperature, in EtOH glasses at 90 K, and in Ar matrices at 12 K. These nitrenes were chosen as suitable models for clarifying the mechanism of intramolecular reactions because attack at the pyrazole ring can occur according to different modes and the asymmetry of ...