Reactivity 3.3 Electron Sharing Reactions

why are alkanes so unreactive

each carbon has 4 sigma bonds - saturated

all bonds are non polar (electronegativity is similar)

H-H and C-H bond enthalpy is high

what are radicals

molecular entities with a single unpaired electron

properties of free radicals

highly reactive

indicated by a single dot

heterolytic fission

unequal splitting of the covalent bond

produces IONS

homolytic fission

equal splitting of the covalent bond

produces RADICALS

in the presence of UV

what is free radical substitution

A 3 step reaction mechanism when a halogen replaces a hydrogen atom.

3 steps of free radical substitution

initiation, propagation, termination

initiation

radical produced

-halogen bond broken by UV, forming 2 radicals

propagation

radicals reacting

- free radicals attack

- produces a alkyl radical, attacks a halogen molecule

termination

radicals removed

- they begin to react with each other

why are radicals not long lasting

they are highly reactive

2 conditions required for radical formation

high temperatures

uv light