Cationic structures radical cations, matrix isolation

The dihydrothiazol-2-ylidene (4) was generated by photolysis of matrix-isolated thiazol-2-carboxylic acid.12 Calculations suggested that the barrier to isomerization to thiazole is about 42.3 kcal mol 1 and that the carbene resembles the related imidazol-2-ylidene in structure. An ab initio study of hydroxyoxiranone predicted that the decarboxylation of the zwitterion (5) to form hydroxycarbene (6) would be favourable in vacuo but not in water.13 A theoretical study showed that dihalosulfenes (X2C=S02) are best viewed as dihalocarbenc-SO complexes with a carbon-sulfur bond order of approximately zero.14 hi a study directed at the elusive thionformic acid (7), tandem mass spectrometric methods were applied to isomeric ethyl thioformates.15 The results suggest that the radical cations generated have the carbene structure [(HS)C(OH)]+ ... 

ESR spectra can provide not only an unambiguous assignment of radicals, but also experimental information about their geometrical and electronic structures and reactions. CW-ESR spectroscopy combined with matrix isolation methods and ionizing radiation (y-ray, X-ray, etc.) is applied to the studies on reactive intermediate radicals including anionic and cationic species trapped in low temperature solid matrices. ESR parameters, especially hyperfine (hf) couplings, are predicted with considerable precision by recent advances in computational methods such as density functional theory (DFT), which affords a valuable bridge between experiment and theory at a most fundamental level. 

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