Electron delocalisation and stabilisation in substituted amino- and hydroxypropynyl radicals

A series of aminopropynes, RCCCH2NH2(R = H, Me, But, Me3Si), RCCCH2N(SiMe3)2, and hydroxypropynes RCCCH2OH (R = H, Me, But, Me3Si, CF3, and EtO2C), were prepared and the corresponding α-aminopropynyl and α-hydroxypropynyl radicals were examined by e.s.r. spectroscopy. For the first series, the C–N bond rotation barriers were determined from the exchange broadening in the spectra and hence radical stabilisation energies were estimated. The spin distribution in these series indicated an extra delocalisation in radicals with captodative substitution.