| Abstract: | Absolute rate constants and their temperature dependence are determined by time-resolved electron spin resonance for the addition of Me3? to 20 and of Me3CO2C?H2 to six mono- and disubstituted alkynes in solution. For Me3? the rate constants show polar alkyne-substituent effects which are, however, weaker than for the corresponding alkenes. For Me3CO2?H2, the rate constants do not vary strongly with alkyne substitution and probably increase with increasing reaction exothermicity. Both radicals react generally slower with alkynes than with alkenes which is discussed in terms of the state correlations. Several vinyl-type radical adducts of Me3? to alkenes are characterized by electron spin resonance, and their spectral data indicate linear or bent configurations of the radical carbon depending on the substitution. |
