Dichroism of absorption and polarization of phosphorescence of molecules of the closed form of nitrobenzospirothiopyran

The spectral-polarization characteristics of absorption and phosphorescence of molecules of the initial form of nitro-substituted indolinospirobenzothiopyran were studied in oriented polyethylene films and in solutions with different polarity. An oscillator model of the electron transitions responsible for the formation of absorption and luminescence spectra was suggested. It was established that the principal differences in the spectral and photophysical properties of the compound studied and its oxygen-containing analog are associated with the fact that the electronegativity of the S atom is lower than that of the O atom. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1143–1146, June, 1997.     

On the closed form of Wigner rotation matrix elements

The closed forms of some rotation matrix elementsd _{m m} ^j (/2) are presented. The closed forms of summation involved two binomials and some special hypergeometric functions are also obtained. The MAPLE V program which calculates d _{m m} ^j (), dm,. (/2) and the help file are given in appendix.Supported in part by the Chiu Feng-Chia research Fund. Thanks are due to the Board of Trustees Chairman Dr. Ying-Ming Liao as well as the Trustee Dr. Charles Chiu-Hsiong Huang and President Dr. Ted C. Yang of Feng-Chia University, Taichung, Taiwan, ROC.     

Inversion vs retention of configuration in gas-phase ammonium ion/alcohol reactions

The potential energy surface for gas-phase reactions of ammonium ion with alcohols was examined by ab initio and DFT methods. Transition structures for inversion (S(N)2) and retention (S(N)F) mechanisms were located for 2-propanol and exo-2-norbornanol. The S(N)F (retention) process was found to be 6-8 kcal/mol higher in energy than the inversion S(N)2 counterpart for the 2-propanol system. The retention process in the 2-exo-norbornanol/ammonium ion system was favored by 1.3 kcal/mol.     

Inversion versus retention of configuration for nucleophilic substitution at vinylic carbon

A high-level computational study using CCSD, CCSD(T), and G2(+) levels of theory has shown that unactivated vinyl substrates such as vinyl chloride would afford gas phase, single-step halide exchange by a pure in-plane sigma-approach of the nucleophile to the backside of the C--Cl sigma bond. Geometry optimization by CCSD/6-31+G* and CCSD(T)/6-31+G* confirms the earlier findings of Glukhovtsev, Pross, and Radom that the S(N)2 reaction of Cl(-) with unactivated vinyl chloride in the gas phase occurs by a sigma attack. Complexation of vinyl chloride with Na(+) does not alter this in-plane sigma preference. However, moderately activated dihaloethylenes such as 1-chloro-1-fluoroethylene undergo gas-phase S(N)2 attack by the accepted pi-route where the nucleophile approaches perpendicular to the plane of the C==C. In the latter case a single-step pi pathway is preferred for the Cl(-) + H(2)C==CFCl reaction. This is the first definitive example at a high level of theory where a single-step pi nucleophilic vinylic substitution is preferred over a multistep mechanism in the gas phase. The activation barriers for these gas-phase single-step sigma- and pi-processes involving both naked anions and Na(+) complexes are, however, prohibitively high. Solvation and the presence of a counterion must play a dominant role in nucleophilic vinylic substitution reactions that proceed so readily in the condensed phase. In solution, nucleophilic vinylic substitution reactions involving electron-withdrawing groups on the carbon--carbon double bond (e.g., -CN, -CHO, and -NO(2)) would almost certainly proceed via a free discrete carbanionic intermediate in accord with experiment.     

On formulas in closed form for Van Vleck expansions

Canonical transformations have been widely used to simplify Hamiltonians and other operators. In molecular and in solid state theory, the so-called Van Vieck expansion is usually employed for this purpose while in theories of particles interacting with fields a combination of canonical transformations in closed form with Van Vleck type expansions has been found effective. For some of the transformations used in applications formulas in closed form are well known. It will be shown here that such formulas can be derived whenever the transformation function is bilinear in the canonical variables, and further that the use of matrix operators makes it possible to simplify these derivations substantially. The Cayley-Hamilton theorem is then used to express the expansions for the matrix operators in closed form. The number of separate operator terms appearing in the formulas thus obtained is the same as the rank of the matrices used. To calculate the coefficients of these operator terms a new type of special functions is introduced. The resulting linear canonical transformations include generalized rotations in both ordinary and phase-space. Explicit results have been obtained for several two- to four-dimensional problems.     

Determining absolute configuration in flexible molecules: a case study

Assigning absolute configuration of molecules continues to be a major problem. Determining absolute configuration in conformationally flexible systems is challenging, even for experts. Here, we present a case study in which we use a combination of molecular modeling, solution NMR, and X-ray crystallography to illustrate why it is difficult to use solution methods alone for configuration assignment. For the case examined, a comparison of calculated and experimental optical rotatory dispersion (ORD) data provides the most straightforward way to assign the absolute configuration.     

Inversion of configuration of alcohols through nucleophilic displacement promoted by nitrate ions.

Inversion of configuration of hydroxy functionalities in biologically significant structures has been performed under mild conditions through nucleophilic displacement by nitrate ion.     

General form of the centrifugal corrections of the spin interactions in diatomic molecules

General forms valid for terms of any type and multiplicity in diatomic molecules are obtained for the first and second correction terms of centrifugal distortions of the spin-orbit, spin-spin and spin-rotation interactions.     

Dipole switching in large molecules described by explicitly time-dependent configuration interaction

In this paper, we report laser-driven charge transfer simulations for Li-(Ph)(n)-CN (n=1,2,3) using the time-dependent configuration interaction single approach. These molecules serve as systematically extendable model systems, in order to investigate the selectivity, and thus controllability, of an ultrashort laser-induced electronic excitation as a function of the molecular size. For example, such control would be needed if a small electronic molecular switch is connected to a larger molecular device. We demonstrate that for larger molecules, the selectivity of the electronic transition is considerably reduced even for rather long pulses due to dynamic polarizations of the molecules. We also show that these dynamic polarizations might be substantially underestimated in few state models.     

Spatial configuration of chain molecules incorporated in liquid crystals and thermodynamic significance

The conformation of chain molecules participating variously in the formation of liquid crystalline mesophase has been elucidated. Two examples are mentioned: (1) the side chain flanking the α-helical backbone of polypeptides, and (2) the spacer joining mesogenic units in mainchain liquid crystals. Flexible segments play an important role in determining thermodynamic properties of these systems.     

Calculation of the ground states of molecules with closed shells via Feynman diagrams

A Feynman-diagram calculation is performed for the ground-state energies of molecules of the XY_p type with closed electron shells. The first two orders in perturbation theory are considered.We are indebted to Dr. V. V. Tolmachev for proposing the topic and for substantial assistance in deriving the results, and also to Dr. U. I. Safronova for constant interest.