Ch4 : Alkyl Halides

Chapter 4: Alcohols and Alkyl Halides

Alkyl Halides

Nomenclature:
Functional group suffix = -halide
Functional group prefix = halo-

Primary, secondary or tertiary ? In a similar fashion to alcohols, alkyl halides are described as primary (1^o), secondary (2^o) or tertiary (3^o) depending on how many alkyl substiutents are attached to the C-X unit.


chloromethane or methyl chloride	bromoethane or ethyl bromide	2-bromopropane or isopropyl bromide	2-bromo-2-methylpropane or tert-butyl bromide
	primary	secondary	tertiary

Physical Properties:

The polar bond creates a molecular dipole that raises the melting points and boiling points compared to alkanes.

Structure:

The alkyl halide functional group consists of an sp³ hybridised C atom bonded to a halogen, X, via a σ bond.
The carbon halogen bonds are typically quite polar due to the electronegativity and polarisability of the halogen.

Reactivity:

The halogens (Cl, Br and I) are good leaving groups.
The polarity makes the C atom electrophilic and prone to attack by nucleophiles via S_N1 or S_N2 reactions.
Bases can remove β-hydrogens and cause 1,2-elimination to form alkenes via E1 or E2 reactions.
Insertion of a metal (esp. Mg) creates an organometalic species.