Intermediate Topic 786 of 1102 Organic Chemistry
Haloalkanes
Alkyl halides containing a carbon-halogen bond, useful in substitution reactions.
In-depth explanation of Haloalkanes
Haloalkanes, also called alkyl halides, have the general formula R-X, where X is a halogen, and the carbon-halogen bond is polarized so that the carbon is electrophilic. The reactivity of the carbon-halogen bond increases in the order C-F less than C-Cl less than C-Br less than C-I because the bond becomes weaker and the halide becomes a better leaving group. Haloalkanes undergo nucleophilic substitution and elimination, and they can be converted into Grignard reagents with magnesium. They are important intermediates in the synthesis of many organic compounds.
Going deeper: Haloalkanes
Key ideas: Haloalkanes (R-X) have a polar C-X bond; C-X bond strength falls from C-F (485 kJ/mol) to C-I (213), so reactivity is RI > RBr > RCl >> RF. They undergo nucleophilic substitution and elimination. Preparations: from alcohols with SOCl2 (clean, gives SO2 and HCl), PCl5 or HX, or by radical halogenation. Boiling points exceed those of alkanes of similar mass but they do not hydrogen bond.
Common mistakes and connections: Students rank reactivity by bond polarity, which gives the wrong order; bond strength and leaving group ability decide it. Another error is saying haloalkanes dissolve in water; they do not. Links to SN1, SN2, E2, Grignard formation and environmental issues such as CFCs.
Visualization of Haloalkanes
Carbon-halogen bond strength falls down the group, so iodoalkanes react fastest in substitution as I- is the best leaving group. The interactive lesson shows this as a live animation or chart.
Worked example and use case
Bromoethane, CH3CH2Br, reacts with aqueous potassium hydroxide by substitution to give ethanol.
Frequently asked questions about Haloalkanes
What is Haloalkanes?
Alkyl halides containing a carbon-halogen bond, useful in substitution reactions.
Is Haloalkanes a beginner, intermediate or advanced topic?
Haloalkanes is a intermediate topic in Organic Chemistry. It builds on the vocabulary of beginner topics in this area.
What should I learn before Haloalkanes?
Study these earlier topics in Organic Chemistry first: Nitration of Benzene, Friedel-Crafts Reactions, Directing Effects.
What comes after Haloalkanes?
The next topics in Organic Chemistry are SN1 Reaction and SN2 Reaction.
Can I practise Haloalkanes with quizzes?
Yes. The interactive lesson includes a self-check question on Haloalkanes, and the Organic Chemistry quiz draws on every topic in this area.
Where Haloalkanes fits in Organic Chemistry
Haloalkanes is topic 58 of 148 in Organic Chemistry.