Maharashtra Board Class 12 Chemistry Chapter 10 Halogen Derivatives PDF Download

Halogen Derivatives

The parent family of organic compounds is hydrocarbon. Replacement of hydrogen atom/s in aliphatic or aromatic hydrocarbons by halogen atom/s results in the formation of halogen derivatives of hydrocarbons.

In this chapter we will study halogen derivatives in a systematic way.

Classification Of Halogen Derivatives

Halogen derivatives of hydrocarbons are classified mainly in two ways.

A. On the basis of hydrocarbon skeleton to which halogen atom is bonded, the halogen derivatives are classified as haloalkanes, haloalkenes, haloalkynes and haloarenes.

B. On the basis of number of halogen atoms, halogen derivatives are classified as mono, di, tri or poly halogen compounds.

We will consider classification of mono halogen derivatives in more detail.

Classification Of Monohalogen Compounds

Monohalogen compounds are further classified on the basis of position of halogen atom and the type of hybridization of carbon to which halogen is attached.

A. Alkyl Halides Or Haloalkanes: In alkyl halides or haloalkanes the halogen atom is bonded to sp³ hybridized carbon which is a part of saturated carbon skeleton. Alkyl halides may be primary, secondary or tertiary depending on the substitution state of the carbon to which halogen is attached.

Teacher's Note

Alkyl halides are very common in industry. For example, in India many pesticides like DDT contain halogen atoms bonded to carbon. These are used to kill harmful insects.

Exam Trick

Remember: Primary (1°) = one carbon attached to carbon-halogen. Secondary (2°) = two carbons attached to carbon-halogen. Tertiary (3°) = three carbons attached to carbon-halogen. Think of it like: 1 friend, 2 friends, 3 friends around the halogen carbon.

Points To Remember

Primary alkyl halides have one alkyl group attached to the carbon with halogen.
Secondary alkyl halides have two alkyl groups attached to the carbon with halogen.
Tertiary alkyl halides have three alkyl groups attached to the carbon with halogen.
The boiling point of alkyl halides increases as we go from primary to tertiary.
Alkyl halides are less polar than alcohols.

B. Allylic Halides: In allylic halides, halogen atom is bonded to a sp³ hybridized carbon atom next to a carbon-carbon double bond.

C. Benzylic Halide: In benzylic halides halogen atom is bonded to a sp³ hybridized carbon atom which is further bonded to an aromatic ring.

D. Vinylic Halides: In vinylic halides halogen atom is bonded to a sp² hybridized carbon atom of aliphatic chain. Vinylic halide is a haloalkene.

E. Haloalkyne: When a halogen atom is bonded to a sp hybridized carbon atom it is a haloalkyne.

F. Aryl Halides Or Haloarenes: In aryl halides, halogen atom is directly bonded to the sp² hybridized carbon atom of aromatic ring.

Teacher's Note

Aryl halides are found in many medicines. For example, some antibiotics contain chlorine or bromine bonded directly to benzene rings. This makes them very useful.

Exam Trick

Remember: Vinylic = on double bond carbon (sp²). Allylic = next to double bond (sp³). Benzylic = next to benzene ring (sp³). Aryl = on benzene ring itself (sp²).

Points To Remember

Benzylic halides are more reactive than alkyl halides.
Vinylic halides are less reactive than alkyl halides.
Aryl halides are much less reactive than alkyl halides.
Allylic halides are more reactive than simple alkyl halides.
The type of halide depends on the hybridization and position of the halogen atom.

Nomenclature Of Halogen Derivatives

The common names of alkyl halides are derived by naming the alkyl group followed by the name of halogen as halide. For example, methyl iodide, tert-butyl chloride.

According to IUPAC system of nomenclature alkyl halides are named as haloalkanes. Aryl halides are named as haloarenes in common as well as IUPAC system. For dihalogen derivative of an arene, prefix o-, m-, p- are used in common name system but in IUPAC system the numerals 1,2 ; 1,3 and 1,4 respectively are used.

Teacher's Note

In India, many common products use halogen derivatives. For example, refrigerators use halogenated compounds. It is important to know their names to understand chemistry better.

Exam Trick

Remember the naming rule: For haloalkanes, the halogen comes as a prefix with the carbon number. For example, 2-chloropropane means chlorine is on carbon number 2 of propane. Count from the end nearest to the halogen.

Points To Remember

In IUPAC names, halogen appears as a prefix, not a suffix.
The carbon bearing halogen gets the lowest number.
If multiple halogens are present, number from the end that gives lowest numbers.
For aromatic compounds, use 1,2 or 1,3 or 1,4 in IUPAC instead of o-, m-, p-.
Always use alphabetical order when multiple different halogens are present.

This is a preview of the first 3 pages. To get the complete book, click below.