Radical Reactions. Chapter 15 Smith. Introduction. A radical is a chemical species with a single unpaired electron in an orbital. Two radicals arise when a bond is cleaved homolytically. Cl-Cl + heat Cl• + Cl•. 1 o , 2 o and 3 o Radicals.
Cl-Cl + heat Cl• + Cl•
Order of stability is the same as for carbocations: a tertiary radical is more stable than a secondary radical, and a secondary radical is more stable than a primary radical
Compounds that prevent radical reactions are called radical inhibitors or radical scavengers.
Vitamin E is a radical scavenger.
All Hydrogens are alike, replacement of any one gives the same product.
Halogenation of an alkane is a substitution reaction.
Rule: We only make monohalogenation products in this course.
Initiation: Two radicals are formed by homolysis of a s bond, starting the rxn.
Propagation: A radical reacts with a reactant, forming a new s bond and
a radical. (A radical makes a radical in propagation sub-steps.
Termination: Two radicals combine to form a stable bond.
Two propagation steps; the first is rate determining.
Use this information to predict the product distribution when more
than one kind of H is present in the substrate.
Tertiary H is easier to remove than secondary, and secondary is
easier to remove than primary H.
Halogenation of a Chiral Compound
Halogenation at Io carbon away from * retains the R configuration.