Gas-Phase Nucleophilic Reactivities of Phenylnitrene (PhN-*) and Sulfur Anion Radicals (S-/.) at sp3 and Carbonyl Carbon

Article abstract of DOI:10.1021/ja00340a010

The reactions of PhN^-/. with a series of carbonyl-containing molecules (aldehydes, ketones, and esters) were shown to proceed via an addition/fragmentation mechanism, PhN^-* + R2C=O -> -)R2> -> PhN=C(O^-)R + *R, producing various acyl anilide anion products.In several cases, the tetrahedral intermediate anion radicals were observed as minor ions.The intrinsic reactivity of the carbonyl-containing molecules was aldehydes > ketones > esters, where similar R groups were involved.The overall exothermicities of these reactions did not appear to play the major role in determining the relative rates (k_rel^C=O) for these reactions.From the reaction of PhN^-* with cyclobutanone, a new type of anion radical, PhN=C(O^-)CH2* (m/z 133) (+ C2H4) was produced; the loss of C2H4 was considered due to the ring strain in the ketone.With cyclopentanone, cyclohexanone, and cycloheptanone, the anion radicals PhN=C(O^-)(CH2)n* (n = 4-6) were the exclusive product ions.PhN^-* was shown to be a poor nucleophile in S_N2 displacement reactions with CH3X molecules (X = Cl, Br, O2CCF3).S^-* was shown to exhibit modest S_N2 nucleophilicity with CH3Cl and CH3Br.The reactions of S^-* with CF3CO2R proceed via both S_N2 displacement and carbonyl addition/fragmentation mechanisms: with R = CH3, the anion products were 65percent CF3CO2^- and 35percent CF3COS^-; from R = C2H5, the product ions were 4percent CF3CO2^- and 96percent CF3COS^-.These data yield the ratio k_CH3/k_C2H5 = 16 for S_N2 displacement by S^-* at these alkyl groups.The reactions of PhN^-* with CO2, COS, CS2, and O2 are also reported.The reaction of PhN^-* with CS2 to produce S^-* as a major channel was used as the source of this atomic anion radical.In several reactions occuring at nearly the collison limit, selectivity was observed for (a) which of two reaction centers were attacked to give products and (b) which of two mechanisms would be dominant in the overall reaction.