Introduction to Haloalkanes & Haloarenes
Haloalkane and haloarenes are hydrocarbons where one or more hydrogen atoms are replaced by halogen atoms. When a hydrogen atom is replaced by an aliphatic hydrocarbon with a halogen atom the compound formed is called haloalkane. Alkyl halide and halogenoalkane are other names for the same thing.
Example of Haloalkanes- Ethyl bromide - CH3CH2 - Br (sp3C)
However, when a hydrogen atom is replaced by a fragrant hydrocarbon the halogen atom compound formed is known as haloarene. Also known as aryl halide or halogenoarene. In haloalkane (R - X), X represents the halogen group. It is attached to the sp3 composite atom of the alkyl group while in haloarene (Ar - X) the halogen is attached to the sp2 composite atom of the aryl group.
Example of Haloarenes- Bromobenzene
Haloalkanes
Haloalkanes are a group of organic compounds that comprise alkane compounds with halogen. There may be one or more halogens in one place.
Haloarenes
Haloarene is a group of organic compounds that contain fragrant compounds with one or more halogen atoms. An alkyl halide is another common name for Haloalkanes.
More importantly, one or more halogen atoms in these compounds bind directly to the scented ring. Aryl chlorides are the most common and important members of this group.
E.g - Bromobenzene - C6H5Br (sp2C)
Differences between Haloalkanes and Haloarenes
Haloalkanes are a group of organic compounds that comprise alkane compounds with halogen. Haloarenes are a group of organisms that consist of aromatic compounds containing one or more halogen atoms. The main difference between haloalkane and haloarenes is that haloalkane is an aliphatic compound containing halogen, while haloarene is a fragrant compound containing halogen.
In addition, haloalkanes do not have fragrant rings, but haloarene does. Haloalkanes can be produced from alkanes using free radical halogenation, from alkenes and alkynes, from alcohol to carboxylic acids, etc. However, the two most common ways to produce haloarene are the direct smell of fragrant rings and the Sandmeyer reaction. Therefore, this is another major difference between haloalkane and haloarene.
Classification
Haloalkanes and haloarenes come in several types. These types can be defined based on the number and location of halogens.
They Can be Classification based on -
Number of hydrogen atoms
Combined with sp3 C — X Bond
Compounds with sp2 C-X Bond
The number of halogens in the alkane or arena forms mono-, di-, or poly-haloalkanes / haloarenes. The position of the halogen in relation to others in the field makes it para, ortho, or meta. The number of hydrogen vs 'R' atoms in a halogen-containing carbon makes it the primary, secondary, or higher.
Use of Haloalkanes and Haloarenes
Some important applications of these combinations are listed below:
These organic compounds have the ability to dissolve non-polar molecules and are thus utilised as solvents.
Many alkyl and aryl halides products are used medicinally. One such example is the compound chloramphenicol, which is used to treat people with typhoid.
Another example is chloroquine, which is very effective in treating malaria. Dichlorodiphenyltrichloroethane (commonly referred to as DDT) is used as an insecticide.
(Image will be uploaded soon)
Haloalkanes and Haloarenes are very useful organic compounds. These are used as solvents, propellants and many other industrial purposes. Haloalkanes and Haloarenes is a basic topic of CBSE Class 12 organic chemistry. It is an easy topic to understand.
Haloalkanes and Haloarenes are halogen derivatives of Alkanes and Arenes. These are also known as alkyl halides and aryl halides respectively. We will discuss the definition of haloalkanes and haloarenes, examples of haloalkanes and haloarenes, differences between haloalkanes and haloarenes and their classification in this article.
What are Haloalkanes?
Haloalkanes are hydrocarbons consisting of aliphatic alkanes with one or more hydrogen atom/s replaced by halogens. In haloalkanes, the halogen atom gets attached to sp3 hybridized carbon atom of alkyl group. A few examples of haloalkanes are given below –
CH3Cl – Methyl Chloride
CH3CH2Br – Ethyl Bromide
What are Haloarenes?
Haloarenes are also hydrocarbons composed of aromatic ring/s with one or more hydrogen atoms/s replaced by halogens. In haloarenes, the halogen atom gets attached to sp3 hybridized carbon atom of alkyl group. A few examples of haloarenes are given below –
(Image will be uploaded soon)
Difference Between Haloalkanes and Haloarenes in Tabular Fo
Classification of Haloalkanes and Haloarenes or Classification of alkyl and aryl halides
Alkyl halides or haloalkanes and aryl halides or haloarenes can be classified on the basis of:
Number of halogen atom/s on an alkyl or aryl halide molecule.
Types of carbon atoms
Hybridization of Carbon atom to which halogen is attached.
On the basis of the Number of halogen atom/s on an alkyl or aryl halide molecule, haloalkanes and haloarenes can be classified into the following two types –
a. Mono Haloalkanes and Mono Haloarenes.
b. Poly Haloalkanes and Poly Haloarenes.
a. Mono Haloalkanes and Mono Haloarenes - These contain one halogen atom in one molecule.
(Image will be uploaded soon)
b. Poly Haloalkanes and Poly Haloarenes – These contain two or more halogen atoms in one molecule. These can be further divided into the following three types –
1. Di Haloalkanes and Di Haloarenes – Contain two Halogens
(Image will be uploaded soon)
2. Tri Haloalkanes and Tri Haloarenes – Contain three Halogens
(Image will be uploaded soon)
3. Tetra Haloalkanes and Tetra Haloarenes – Contain four Halogens
(Image will be uploaded soon)
On the basis of types of Carbon atoms, these can be classified into following three types –
Primary Alkyl Halide - halogen atom is attached with primary carbon.
(Image will be uploaded soon)
Neopentyl Bromide
Secondary Alkyl Halide – halogen atom attached with secondary carbon.
(Image will be uploaded soon)
Secondary-Butyl Bromide
Tertiary Alkyl Halide – halogen atom attached with a tertiary carbon.
(Image will be uploaded soon)
Tertiary-Butyl Bromide
On the basis of hybridization of Carbon atom to which Halogen is attached, Haloalkanes and Haloarenes can be classified into following two types -
a. Halogen attached to sp3 hybridized carbon
b. Halogen attached to sp2 hybridized carbon
a. Halogen Attached to sp3 Hybridized Carbon - On this basis Alkyl Halide and Aryl Halide can be classified into following three types-
Alkyl Halide - Halogen attached to alkyl chain.
CH3-CH2-CH2-Cl
N-Propyl Chloride
Allylic Halide – Halogen attached to that sp3 hybridized carbon which is adjacent to C=C.
(Image will be uploaded soon)
Benzylic Halide - Halogen attached to that sp3 hybridized carbon which is attached to the benzene ring.
(Image will be uploaded soon)
b. Halogen Attached to sp2 Hybridized Carbon - On this basis alkyl halide and aryl halide can be classified into following two types -
Vinyl Halide – Halogen attached with sp2 hybridized carbon.
(Image will be uploaded soon)
Aryl Halide - Halogen attached to sp2 hybridized carbon in an aromatic ring.
(Image will be uploaded soon)
Haloalkanes and Haloarenes Other Application
These are used as hydrophobic solvents in chemistry.
These are used in organic synthesis.
These are used in industry.
Chloroquine is very useful in the treatment of malaria.
DDT is used as an insecticide.
These have adverse effects on the environment as well such as CFC (chlorofluorocarbon) is a major cause of depletion of ozone layer.
FAQs on Haloalkanes and Haloarenes
1. What is the fundamental difference between haloalkanes and haloarenes concerning the carbon-halogen (C-X) bond?
The key difference lies in the hybridization of the carbon atom attached to the halogen. In haloalkanes, the halogen is attached to an sp³-hybridized carbon atom. In haloarenes, the halogen is attached to an sp²-hybridized carbon atom of the aromatic ring. This leads to a shorter, stronger C-X bond in haloarenes due to partial double bond character from resonance, making them less reactive in nucleophilic substitution reactions.
2. Which topics in Haloalkanes and Haloarenes are considered high-weightage for the JEE Advanced 2026 exam?
For JEE Advanced 2026, students should focus on high-weightage concepts within this chapter, which often include:
- Mechanisms and stereochemistry of SN1 and SN2 reactions, including solvent effects.
- Reactivity and mechanism of nucleophilic and electrophilic substitution in haloarenes.
- Named reactions like Sandmeyer, Gattermann, Finkelstein, Swarts, Wurtz, and Fittig reactions.
- The preparation and synthetic applications of Grignard reagents.
- Stereochemical concepts like enantiomers, diastereomers, and racemization.
3. Why are haloarenes significantly less reactive than haloalkanes towards nucleophilic substitution?
Haloarenes are less reactive towards nucleophilic substitution due to several key factors:
- Resonance Effect: The C-X bond in haloarenes acquires a partial double-bond character due to resonance, making it stronger and harder to break.
- Hybridization: The sp² hybridized carbon in haloarenes is more electronegative than the sp³ carbon in haloalkanes, holding the C-X bond electrons more tightly.
- Instability of Phenyl Cation: In a potential SN1 pathway, the resulting phenyl cation is highly unstable and does not form readily.
- Electronic Repulsion: The electron-rich benzene ring can repel the incoming electron-rich nucleophile.
4. What is the role of the solvent in determining whether an SN1 or SN2 reaction mechanism is favoured?
The choice of solvent is critical in directing the reaction pathway. A polar protic solvent (e.g., water, ethanol) stabilises both the carbocation intermediate and the leaving group through solvation, thus strongly favouring the SN1 mechanism. Conversely, a polar aprotic solvent (e.g., acetone, DMSO) solvates the cation but not the anion (nucleophile), leaving the nucleophile more 'naked' and reactive, which favours the bimolecular SN2 mechanism.
5. Although halogens are deactivating, why are they ortho-, para-directing in electrophilic aromatic substitution?
This is a classic exception in aromatic chemistry. The effect is due to the competition between two opposing factors:
- Inductive Effect (-I): Halogens are highly electronegative and pull electron density from the benzene ring, deactivating it towards electrophilic attack.
- Resonance Effect (+R): The lone pairs on the halogen atom can be delocalised into the ring, increasing electron density specifically at the ortho and para positions.
6. How does the concept of ambident nucleophiles lead to different products when reacting with a haloalkane?
Ambident nucleophiles, such as the cyanide ion (CN⁻) and nitrite ion (NO₂⁻), have two nucleophilic centres. The product formed depends on the reaction conditions. For example:
- When a haloalkane reacts with KCN (ionic), the attack occurs through the carbon atom, forming an alkyl cyanide (R-CN) as the major product.
- When it reacts with AgCN (covalent), the nitrogen's lone pair is more available for attack, forming an alkyl isocyanide (R-NC) as the major product.
7. Explain the mechanism and a key application of the Sandmeyer reaction for preparing aryl halides.
The Sandmeyer reaction is a method to synthesise aryl halides from primary aromatic amines. The mechanism involves:
1. Conversion of a primary aromatic amine (e.g., aniline) into a benzenediazonium salt using NaNO₂ and a mineral acid (like HCl) at low temperatures (0-5°C).
2. The diazonium salt is then treated with a cuprous halide (CuX), where X is Cl or Br, which replaces the diazonium group with the halide.
Its key application is the synthesis of aryl chlorides and bromides, which can be difficult to produce with desired yields through direct halogenation.
8. What are enantiomers and how are they relevant to the stereochemistry of haloalkanes?
Enantiomers are stereoisomers that are non-superimposable mirror images of each other. They arise in haloalkanes when a carbon atom is bonded to four different groups, making it a chiral centre. For example, 2-bromobutane is chiral and exists as a pair of enantiomers. This is highly relevant in SN1 and SN2 reactions, where an SN2 reaction on a chiral centre leads to an inversion of configuration, while an SN1 reaction typically leads to a racemic mixture (equal amounts of both enantiomers).
