Tailored Nitroxide Radicals and Biradical Containing <Superscript>13</Superscript>C Enriched Acetylene Groups: ENDOR and DFT Investigation

A specially synthesized nitroxide biradical R₅-C≡¹³C-(p-C₆H₄)₂-¹³C≡C-R₅ (B4) and two radicals, R₅-C≡¹³CH (RCC) and R₅-C≡¹³C-C₆H₅ (RCCPh), where R₅ is 1-oxyl-2,2,5,5-tetramethyl-pyrroline group, have been studied by X- and W-band electron paramagnetic resonance (EPR) spectroscopy, and by W-band electron-nuclear double resonance (ENDOR). Spin density distribution and hyperfine splitting (hfs) constants on ¹³C atoms were experimentally determined and also calculated using ORCA 3.0.3 program package. The biradical and radicals geometries were optimized on UKS/B3LYP/cc-pVDZ level. Hfs constants were calculated using density functional theory (DFT) with PBE0 functional and N07D, and were compared with the experimental value of the hfs constant on ¹³C atoms, measured from ENDOR spectra. It is concluded that at small values of the exchange integral as J ≤ a/2 ≈ 7–8 G, the current quantum chemical approaches do not allow determining precise values of the hfs constants on the ¹³C atoms in the bridge connecting two paramagnetic nitroxide rings of the biradical.     

Induced decomposition of acetylcyclohexylsulfonyl peroxide

The kinetics of thermal decomposition of acetylcyclohexylsulfonyl peroxide is studied in an-decane solution in an oxygen atmosphere (303–333 K) and under anaerobic conditions (313–333 K); the reaction products are also studied in a cyclohexane solution under oxygenfree conditions (323 K). In the absence of oxygen, the reaction is found to proceedvia a chain-radical mechanism. Some kinetic parameters of the process are determined.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1049–1052, June, 1995.This work was supported by the Russian Foundation for Basic Research (Project No. 93-03-5231).     

Electron diffraction,x-ray diffraction,and CNDO/2 analysis of the conformations,molecular geometry,and internal rotation potentials of aryldichloro- and aryldibromoarsines

A structural study was carried out on o-ClC₆H₄AsCl₂ (I), o-BrC₆H₄AsBr₂ (II), C₆H₅AsBr₂ (III), and p-BrC₆H₄AsBr₂ (IV). The normal mode frequencies and shapes were calculated and gas-phase electron diffraction was used to establish the geometric parameters of III and IV. The structure of IV was determined by x-ray diffraction structural analysis. The experimental results for I–IV (I and II were studied in previous work) were interpreted on the basis of CNDO/2 calculations for I–III.A. E. Arbuzov Institute of Organic and Physical Chemistry, Kazan Branch, Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 30, No. 5, pp. 61–69, September–October, 1989.