Radicals in which the odd electron is located on doubly bonded carbon such as vinyl (CH2=CH*) or phenyl (*C6H5) radical, cannot be stabilized by hyperconjugation or by resonance and hence are usually very shortlived. These radicals are even less stable than methyl radical. This has been supported by bond dissociation energy values of the R-H bonds.

In Vinyl Ch2=CH- carbon is sp2 hybridized (double bond ) and hence electron deficient. So it becomes difficult for thrm  to loose an electron to from vinyl radical or loose an electron pair to form vinyl carbocation