Halogenoalkanes

Halogenoalkanes (also called haloalkanes or alkyl halides) are organic compounds in which one or more hydrogen atoms of an alkane have been replaced by halogen atoms (F, Cl, Br, or I). They have the general formula CₙH₂ₙ₊₁X (for monohalogenoalkanes), where X is a halogen.

Halogenoalkanes are far more reactive than alkanes because the C-X bond is polar — the halogen is more electronegative than carbon, creating a δ+ carbon that is susceptible to attack by nucleophiles.

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Classification

Halogenoalkanes are classified as primary, secondary, or tertiary depending on how many carbon atoms are bonded to the carbon that carries the halogen:

Classification	Carbon Bearing the Halogen	Example
Primary (1°)	Bonded to one other carbon (or none, as in CH₃Cl)	CH₃CH₂Br (bromoethane)
Secondary (2°)	Bonded to two other carbons	(CH₃)₂CHBr (2-bromopropane)
Tertiary (3°)	Bonded to three other carbons	(CH₃)₃CBr (2-bromo-2-methylpropane)

This classification is critically important because it determines which reaction mechanism occurs.

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Physical Properties