Electron delocalisation and stabilisation in substituted amino- and hydroxypropynyl radicals

Abstract

A series of aminopropynes, RCCCH₂NH₂(R = H, Me, Bu^t, Me₃Si), RCCCH₂N(SiMe₃)₂, and hydroxypropynes RCCCH₂OH (R = H, Me, Bu^t, 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.