What chemical starts off the chain reaction in the initiation step of an anti-markovnikov radical addition?

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Answer 1 · 2015-08-08T15:53:20

The initiator in a free radical addition reaction is a substance that decomposes into free radicals under mild conditions.

An initiator should have bonds with low dissociation energies (e.g. #"O-O"# bonds) or form stable molecules (e.g. #"N"_2#) on dissociation.

Common initiators are:

Azo compounds

Azo compounds (#"R-N≡N-R"#) decompose into nitrogen and two free radicals on heating or irradiation.

#"R-N≡N-R " stackrel(color(blue)(Δ))stackrelcolor(blue)("or"color(white)(1)hν)(→) "R·" + "N≡N" + "·R"#

AIBN (azo-bis-isobutyronitrile) is a convenient free radical initiator because it decomposes at relatively low temperatures.

Organic peroxides

Two common peroxide initiators are

(a) Di-t-butyl peroxide

(from chemed.chem.purdue.edu)

(b) Benzoyl peroxide

enter image source here
(from research.cm.utexas.edu)