: The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

Although thousands of quantitative structure–activity and structure–property relationships (QSARs/QSPRs) have been published, as well as numerous papers on the correct procedures for QSAR/QSPR analysis, many analyses are still carried out incorrectly, or in a less than satisfactory manner. We have identified 21 types of error that continue to be perpetrated in the QSAR/QSPR literature, and each of these is discussed, with examples (including some of our own). Where appropriate, we make recommendations for avoiding errors and for improving and enhancing QSAR/QSPR analyses.

How not to develop a quantitative structure–activity or structure–property relationship (QSAR/QSPR)

Support vector machines and its applications in chemistry

In 2009, we reported C−halogen reductive elimination reactions from dinuclear Pd(III) complexes and implicated dinuclear intermediates in Pd(OAc)2-catalyzed C−H oxidation chemistry. Herein, we report results of a thorough experimental and theoretical investigation of the mechanism of reductive elimination from such dinuclear Pd(III) complexes, which establish the role of each metal during reductive elimination. Our results implicate reductive elimination from a complex in which the dinuclear core is intact and suggest that redox synergy between the two metals is responsible for the facile reductive elimination reactions observed.

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Bimetallic Reductive Elimination from Dinuclear Pd(III) Complexes

A theoretical study of the complexes formed by hypohalous acids (HOX, X = F, Cl, Br, I, and At) with three nitrogenated bases (NH3, N2, and NCH) has been carried out by means of ab initio methods, up to MP2/aug-cc-pVTZ computational method. In general, two minima complexes are found, one with an OH···N hydrogen bond and the other one with a X···N halogen bond. While the first one is more stable for the smallest halogen derivatives, the two complexes present similar stabilities for the iodine case and the halogen-bonded structure is the most stable one for the hypoastatous acid complexes.

Competition of Hydrogen Bonds and Halogen Bonds in Complexes of Hypohalous Acids with Nitrogenated Bases

At the averaged quadratic coupled-cluster (AQCC) level, a number of selected rare gas (Rg) containing systems have been studied using the quantum theory of atoms in molecules (QTAIM), natural bond orbital (NBO), and several other analysis methods. According to the criteria for a covalent bond, most of the Rg–M (Rg = He, Ne, Ar, Kr, Xe; M = Be, Cu, Ag, Au, Pt) bonds in this study are assigned to weak interactions instead of van der Walls or covalent ones. Our results indicate that the rare gas bond is a new kind of weak interaction, like the hydrogen bond for example.

On the Covalent Character of Rare Gas Bonding Interactions: A New Kind of Weak Interaction

Prediction of toxicity of nitrobenzenes using ab initio and least squares support vector machines.

The static and dynamic stereochemistry of biphenyl (1), 1-phenylnaphthalene (2), 1-phenylanthracene (3), 9-phenylanthracene (4), 1,1′-binaphthyl (5), 1,1′-naphthylanthracene (6), 1,9′-naphtylantracene (7), 1,1′-bianthryl (8), 9,9′-bianthryl (9) and 1,9′-bianthryl (10) were examined using ab initio molecular orbital (MO) and the Becke, Lee, Yong and Parr density functional (B3LYP) methods. The structure of the ground states, the activation energies for rotation about the σ-bonds of compounds 1–10 and the nature of deformation of aromatic rings in the equilibrium structures and saddle point geometries were also investigated. Studies on the HF/6-31G*//Hf/3-21G, MP2/6-31G*//HF/3-21G and B3LYP/6-31G*//HF/3-21G levels of theory confirm that compounds 5, 6 and 8 should racemize preferably the anti path, (with about 9 kcal mol−1 lower energy than the syn path). However, the resulted racemization energy for compound 5 through the syn path is found to contradict the previously reported semi-empirical calculations.

Ab initio study of the structures and dynamic stereochemistry of biaryls

The oils obtained by steam distillation of the flowers and leaves of Tanacetum polycephalum growing wild in Iran were investigated by a combination of GC and GC–MS. About 10 compounds in the flowers and 10 compounds in the leaves have been identified. The main constituents of the oil of the flowers were camphor (59.1%), camphene (14.9%) and 1,8-cineole (10.1%), whereas the leaves oil comprised mainly camphor (53.5%), bornyl acetate (12.1%), camphene (10.9%), 1,8-cineol (7.8%) and borneol (6.1%). Copyright © 1999 John Wiley & Sons, Ltd.

Chemical composition of the essential oil of Tanacetum polycephalum (Schultz Bip. ssp. heterophyllum)

The conformational and structural properties of the inhalational anesthetic isoflurane (1-chloro-2,2,2-trifluoroethyl difluoromethyl ether) have been probed in a supersonic jet expansion using Fourier-transform microwave (FT-MW) spectroscopy. Two conformers of the isolated molecule were identified from the rotational spectrum of the parent and several (37)Cl and (13)C isotopologues detected in natural abundance. The two most stable structures of isoflurane are characterized by an anti carbon skeleton (τ(C(1)-C(2)-O-C(3)) = 137.8(11)° or 167.4(19)°), differing in the trans (AT) or gauche (AG) orientation of the difluoromethyl group. The conformational abundances in the jet were estimated from relative intensity measurements as (AT)/(AG) ≈ 3:1. The structural preferences of the molecule have been rationalized with supporting ab initio calculations and natural-bond-orbital (NBO) analysis, which suggest that the molecule is stabilized by hyperconjugative effects. The NBO analysis of donor-acceptor (LP → σ*) interactions showed that these stereoelectronic effects decrease from the AT to AG conformations, so the conformational preferences can be accounted for in terms of the generalized anomeric effect.

/pdf/structural-evidence-of-anomeric-effects-in-the-anesthetic-5a2e2xtu5u.pdf

Davood Nori-Shargh

Papers

On the Covalent Character of Rare Gas Bonding Interactions: A New Kind of Weak Interaction

Prediction of toxicity of nitrobenzenes using ab initio and least squares support vector machines.

Ab initio study of the structures and dynamic stereochemistry of biaryls

Chemical composition of the essential oil of Tanacetum polycephalum (Schultz Bip. ssp. heterophyllum)

Structural evidence of anomeric effects in the anesthetic isoflurane.