I. D. Morozova

Ab initio calculation of 14N and 35Cl nuclear quadrupole coupling constants in aziridine and Cl-aziridine

Abstract Ab initio calculations of electric field gradients (EFG) at 14 N and 35 Cl nuclei and conversion to the corresponding nuclear quadrupole coupling constants are reported for aziridine and Cl-aziridine molecules. The structural parameters for Cl-aziridine used for these calculations are obtained as a result of gradient optimization at the HF/4–31G ∗ level. The mutual orientation of the molecular axes and principal axes of the EFG tensor is presented. To evaluate the main contribution from various bonds and lone pairs to the EFG tensor components, a localized molecular orbital (LMO) analysis is made. The comparison of the results of the calculation with experiment is discussed.

Nonempirical calculations of NQR parameters in some three-membered rings

Abstract Ab initio calculations (RHF/6–31G∗) of the electric field gradients (EFGs) at 14N,17O, 2H and 33S and the corresponding nuclear quadrupole coupling constants (NQCCs) are reported for a number of three-membered rings containing atoms of the first and the second rows. The results of the calculations are in good agreement with the available experimental data. The orientations of the principal axes of the EFG tensor at the quadrupole nuclei are determined. The origin of the EFG is analyzed within the framework of the LMO approach. To compare the charge density distributions in aziridine and Cl-aziridine, the charge density maps are obtained using the canonical molecular orbitals.

Ab initio calculations of nitrogen containing free radicals: The geometrical parameters of HFNÖ, H2CNÖ and HFCNÖ radicals

Abstract Geometrical parameters of HFNO, H 2 CNO, ( Z )-HFCNO and ( E )-HFCNO radicals have been calculated by the unrestricted Hartree-Fock metho

Effect of the environment of phosphorus on the distribution of spin density in phosphoniminoxyls

On the basis of an analysis of EPR spectra and quantum-chemical calculations, it was shown that a significant change of the hyperfine splitting a31P in phosphoniminoxyls during replacement of alkoxy groups at the phosphorus atom by alkyl groups is mainly governed by electronic factors of substituents at the phosphorus atom.

Nonempirical calculations of NQR spectrum parameters of azetidine

The components of the14N electric field gradient (EFG) tensor, the corresponding nuclear quadrupole coupling constant (NQCC) χ, and the asymmetry parameter η of azetidine were calculated using the restricted Hartree-Foek-Roothaan method, The geometry of azetidine was optimized with the 4–31G basis set, and the values of the ring puckering angle (θ) and the angle between the N-H bond and the CNC plane (β) were refined with the 6–31G* basis set. The effect of choice of geometry on calculated NQR parameters was studied. To clarify the origin of EFG at the nitrogen atom nucleus, the contributions from individual bond orbitals and lone electron pairs to the EFG tensor componentseqii were calculated in the framework of the LMO approach. It was demonstrated that the 4-31G + 6–31G*//6–31G* level calculations give NQCC and η values of azetidine that are in good agreement with the results of MW spectroscopy.

Analysis of the hyperfine structure of the EPR spectrum of the radical ions of aryl- and diaryldiazocyanides

EPR and quantum chemical methods have been used to establish the nature of the distribution of spin density in electrochemically generated radical anions of diaryldiazocyanides. For the symmetrical diphenyldiazocyanides the unshared electron is distributed over the entire molecule, whereas the introduction of a bridge between the benzene rings leads to the localization of the unshared electron only on one fragment of the molecule.

Calculating the geometrical parameters of iminoxy radicals using the unrestricted Hartree-Fock-Roothaan method. 2. The radicals Z-HFC=NO. and E-HFC=NO.

Conclusions1.The unrestricted Hartree-Fock method with corrected bond lengths was used to determine the equilibrium geometrical configurations of the radicals Z-HFC=NO. and E-HFC=NO..2.The difference between the energies of the diasteromeric forms of the HFC=NO. radical is ∼1.6 kcal/mole; the Z form is the more stable.3.When the Z-HFC=NO. and E-HFC=NO. radicals form from the diamagnetic molecules Z-HFC=NOH and E-HFC=NOH, the length of the =N-O bond decreases ∼0.15 Å, the C=N-O angle widens ∼10°, while the geometrical configuration of the HFC=N-group changes insignificantly.

Calculations of geometric parameters of nitroxide radicals H2N\(\dot O\), HFN\(\dot O\), and F2N\(\dot O\) by the unrestricted Hartree-Fock-Roothaan method

Conclusions1.We have analyzed the models and approximations used to describe the geometric structure of nitroxide radicals.2.We have determined the geometric configurations of the radicals H2NO, HFNO, and F2NO and have estimated the errors in the calculation of the structure parameters in different basis sets.3.We have shown that the basis 4-31G + BF, containing s and p type bond functions, allows us to determine the configuration of the nitroxide group within ∿0.04 å and ∿4‡,

Calculation of the geometrical parameters of iminoxy radicals by the unrestricted Hartree-Fock-Roothaan method

Conclusions1.The approach considered can determine the equilibrium geometrical parameters of iminoxyl H2CNO. to within 0.02 Å and 2° for the bond lengths and valence angles, respectively.2.On forming the radical H2CNO. from the parent oxime the bond length r(N-O) decreases by 0.2 Å, the angle CNO increases by about 15°, and the structural characteristics of the fragment H2C=N- remain practically unchanged.