0000000000496591
AUTHOR
Reijo Mäkelä
ESR, ENDOR and TRIPLE resonance studies on radical reactions of 1,4-benzoquinone and 1,4-hydroquinone in alkaline methanol and liquid ammonia
The relative signs and absolute values of the hyperfine coupling constants of different methoxy-1,4-benzoquinones were measured by ESR, ENDOR and TRIPLE resonance spectroscopy. Reactions of 1,4-benzoquinone and 1,4-hydroquinone with methanol took place in alkaline methanol, giving rise to methoxy-substituted 1,4-benzoquinones. The same substitution reaction occurred in a mixture of ammonia and methanol. The reactions depended on temperature and the alkali concentration. Coupling constants were assigned by the modified additivity relationship method. An extremely small line width of 0.014 G was measured in the ESR spectrum of deuterated 2,5-dimethoxy-1,4-benzoquinone.
Re-investigation of the conformational interconversion of the 1,2,3,6,7,8-hexahydropyrene cation radical by EPR, ENDOR and TRIPLE spectroscopy
The conformational interconversion of the 1,2,3,6,7,8-hexahydropyrene cation radical has been re-examined by EPR, ENDOR and TRIPLE spectroscopy, and the Arrhenius plot is presented for a wider temperature range than that used earlier. The EPR spectra were measured from 143 to 369 K and the ENDOR spectra from 143 to 263 K. The thermodynamic constants of the conformational interconversion of the cation radical were determined on the basis of the temperature-dependent spectra. The high-resolution spectra clearly show that there are two overlapping spectra at low temperature, and this is confirmed by simulation.
Comparison of spin density calculation methods for various alkyl-substituted 9,10-anthraquinone anion radicals in the solution phase
EPR and ENDOR spectra were recorded for 2-methyl-9,10-anthraquinone (2-methylAQ), 2-ethylAQ, 2-tertbutylAQ and 2,3-dimethylAQ anion radicals in the solution phase. The EPR spectra were simulated with the help of ENDOR data. The experimental isotropic hyperfine coupling constants (IHFCs) were compared with calculated values from semi-empirical INDO, spin-restricted AM1/CI and B3PW91 density-functional methods. The best computational methods for the IHFCs were the semi-empirical AM1/CI method and the B3PW91 density-functional method with a large basis set.
EPR, ENDOR and TRIPLE resonance of amino-substituted 9,10-anthraquinone radicals and the rotation of the amino groups in the solution phase
EPR, ENDOR and TRIPLE resonance spectra were recorded for 1-amino-9,10-anthraquinone (1-aminoAQ), 2-aminoAQ, 1,2-diaminoAQ, 1.4-diaminoAQ, 1,5-diaminoAQ and 2,6-diaminoAQ anion radicals in the solution phase. The rotation of the amino groups is discussed with reference to the experimental data. Rotation barrier calculations were carried out using B3PW91/3-21G* density functional method. The amino groups at positions 1, 4, 5, 8 were found not to be in rotational movement up to the EPR time-scale.
Electron paramagnetic resonance, ENDOR and TRIPLE resonance study of some 9,10-anthraquinone radicals in solution
EPR, ENDOR and TRIPLE resonance spectra were recorded for 1,8-dihydroxy-3-methyl-9,10-anthraquinone and 9,10-anthraquinone-2-carboxylic acid anion radicals and the 9,10-anthraquinol-2-carboxylic acid cation radical. EPR spectra were recorded for the 5,8-dideuterio-1,4-dideuterioxy-9,10-anthraquinone anion radical, the 6,7-dideuterio-1,4-dideuterioxy-9,10-anthraquinone anion radical and the 1,4-dihydroxy-9,10-anthraquinol cation radical. The coupling contants of the 1,4-dihydroxy-9,10-anthraquinone anion radical were assigned by deuteriation.