Haloalkanes

Lesson

Part 1 — alkanes in which halogen atoms replace hydrogen: names, bonds, preparation and physical properties.

In this lesson you will

Classify haloalkanes and name mono-, di- and tri-halo derivatives by common and IUPAC systems
Explain the polarity, length and strength of the C–X bond
Write equations for preparing haloalkanes from alkanes, alkenes, alcohols, by halide exchange and by the Hunsdiecker reaction
Explain trends in boiling point and solubility

Table of familiar haloalkanes and their uses
Compound	Use
Chloroethane	Local anaesthetic spray in sports
Halothane, CF₃CHBrCl	Inhaled general anaesthetic
Dichloromethane	Paint stripper and solvent
Iodoform	Antiseptic
Freons	Former refrigerants

Concept

Classification

By the number of halogen atoms: mono-, di- (geminal: both on one C; vicinal: on adjacent C), tri- and poly-halo compounds. Monohaloalkanes ( $\ce{C_nH_{2n+1}X}$ ) are classified by the carbon bearing X.

Table classifying haloalkanes
Class	Carbon bearing X	Example
Primary (1°)	Joined to one other C	CH₃CH₂CH₂Cl
Secondary (2°)	Joined to two other C	CH₃CHBrCH₃
Tertiary (3°)	Joined to three other C	(CH₃)₃CI
Allylic	sp³ C next to C=C	CH₂=CHCH₂Br
Benzylic	sp³ C next to a benzene ring	C₆H₅CH₂Cl
gem-Dihalide	Two X on one C	CH₃CHCl₂
vic-Dihalide	X on adjacent C	CH₂BrCH₂Br

Concept

Common and IUPAC names

IUPAC: halogen as a prefix (fluoro, chloro, bromo, iodo) with a locant on the longest chain; prefixes in alphabetical order. Common names: alkyl group + halide.

Table of common and IUPAC names of haloalkanes
Structure	Common name	IUPAC name
CH₃CH₂CH₂Br	n-Propyl bromide	1-Bromopropane
(CH₃)₂CHCH₂Cl	Isobutyl chloride	1-Chloro-2-methylpropane
(CH₃)₃CBr	tert-Butyl bromide	2-Bromo-2-methylpropane
CH₂Cl₂	Methylene chloride	Dichloromethane
CHCl₃	Chloroform	Trichloromethane
CHI₃	Iodoform	Triiodomethane
CH₃CHBr₂	Ethylidene bromide	1,1-Dibromoethane

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