Chemistry Classification and Nomenclature of Haloalkanes and Haloarenes
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Class 12 Chapter 10 Haloalkanes and Haloarenes

Classification and Nomenclature of Haloalkanes and Haloarenes

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Topics Covered :

● Introduction
● Classification
● On the Basis of Number of Halogen Atoms
● Compounds Containing `sp^3 C—X` Bond `(X= F, Cl, Br, I)`
● Compounds Containing `sp^2 C—X` Bond
● Nomenclature

Introduction :

`color{green}("Definition ")` The replacement of hydrogen atom(s) in a hydrocarbon, aliphatic or aromatic, by halogen atom(s) results in the formation of alkyl halide (haloalkane) and aryl halide (haloarene), respectively.

`=>` Haloalkanes contain halogen atom(s) attached to the `color{red}(sp^3)` hybridised carbon atom of an alkyl group.

`=>` Haloarenes contain halogen atom(s) attached to `sp^2` hybridised carbon atom(s) of an aryl group.

`=>` Many halogen containing organic compounds occur in nature and some of these are clinically useful.

`=>` They are used as solvents for relatively non-polar compounds and as starting materials for the synthesis of wide range of organic compounds.

`=>` Chlorine containing antibiotic, chloramphenicol, produced by soil microorganisms is very effective for the treatment of typhoid fever.

`=>` Our body produces iodine containing hormone, thyroxine, the deficiency of which causes a disease called goiter.

`=>` Synthetic halogen compounds, viz. chloroquine is used for the treatment of malaria; halothane is used as an anaesthetic during surgery.

`=>` Certain fully fluorinated compounds are being considered as potential blood substitutes in surgery.
Q 3201734628

Explain alkyl halide and aryl halide with example

Solution:

The replacement of hydrogen atom(s) in a hydrocarbon, aliphatic or aromatic, by halogen atom(s) results in the formation of alkyl halide (haloalkane) and aryl halide (haloarene), respectively.

`=>` Haloalkanes contain halogen atom(s) attached to the `sp^3` hybridised carbon atom of an alkyl group.

`=>` Haloarenes contain halogen atom(s) attached to `sp^2` hybridised carbon atom(s) of an aryl group.

Classification :

Haloalkanes and haloarenes may be classified as follows :

On the Basis of Number of Halogen Atoms :

`=>` These may be classified as mono, di, or polyhalogen (tri-, tetra-, etc.) compounds depending on whether they contain one, two or more halogen atoms in their structures. For example : See fig.

Monohalocompounds may further be classified according to the hybridisation of the carbon atom to which the halogen is bonded, as discussed below.

Compounds Containing `sp^3 C—X` Bond `(X= F, Cl, Br, I)` :

This class includes

(a) `color{green}("Alkyl Halides or Haloalkanes" R—X)` : In alkyl halides, the halogen atom is bonded to an alkyl group `(R)`.

● They form a homologous series represented by `color{red}(C_nH_(2n)+1X)`.

● They are further classified as primary, secondary or tertiary according to the nature of carbon to which halogen is attached.


`color{red}(underset(text{Primary} (1^0))(R' - underset( underset(H)(|)) overset( overset(R')(|))C- X) \ \ \ \ \ underset( text{secondary } (2^0))(R'' - underset( underset(H)(|)) overset(overset(R')(|))C-X) \ \ \ \ \ \ \ underset(text{Tertiary}(3^0)) (R'' - underset(underset(R''')(|)) overset(overset(R')(|))C-X))`

(b) `color{green}("Allylic Halides ")` These are the compounds in which the halogen atom is bonded to an `color{red}(sp^3)`-hybridised carbon atom next to carbon-carbon double bond `color{red}(C=C)` i.e. to an allylic carbon. See fig.1.

(c) `color{green}("Benzylic Halides ")` These are the compounds in which the halogen atom is bonded to an `color{red}(sp^3)`-hybridised carbon atom next to an aromatic ring. See fig.2.
Q 3211734629

Define the terms alkyl halides , allylic halides and benzylic halides with examples

Solution:

(a) `"Alkyl Halides or Haloalkanes" R—X` : In alkyl halides, the halogen atom is bonded to an alkyl group `(R)`.

● They form a homologous series represented by `(C_nH_(2n)+1X)`.

● They are further classified as primary, secondary or tertiary according to the nature of carbon to which halogen is attached.


`underset(text{Primary} (1^0))(R' - underset( underset(H)(|)) overset( overset(R')(|))C- X) \ \ \ \ \ underset( text{secondary } (2^0))(R'' - underset( underset(H)(|)) overset(overset(R')(|))C-X) \ \ \ \ \ \ \ underset(text{Tertiary}(3^0)) (R'' - underset(underset(R''')(|)) overset(overset(R')(|))C-X)`

(b) `"Allylic Halides "` : These are the compounds in which the halogen atom is bonded to an `sp^3`-hybridised carbon atom next to carbon-carbon double bond `C=C` i.e. to an allylic carbon.

(c) `"Benzylic Halides "` : These are the compounds in which the halogen atom is bonded to an `sp^3`-hybridised carbon atom next to an aromatic ring.

Compounds Containing `sp^2 C—X` Bond :

This class includes :

(a) `color{green}("Vinylic Halides ")` These are the compounds in which the halogen atom is bonded to an `color{red}(sp^2)`-hybridised carbon atom of a carbon-carbon double bond `color{red}(C = C)`. See fig.1.

(b) `color{green}("Aryl Halides" )` These are the compounds in which the halogen atom is bonded to the `color{red}(sp^2)`-hybridised carbon atom of an aromatic ring.
Q 3211834720

Define the terms vinylic halides and aryl halides with examples

Solution:

(a) `"Vinylic Halides "` These are the compounds in which the halogen atom is bonded to an `sp^2`-hybridised carbon atom of a carbon-carbon double bond `C = C`.

(b) `"Aryl Halides" ` These are the compounds in which the halogen atom is bonded to the `sp^2`-hybridised carbon atom of an aromatic ring.

Nomenclature :

`color{green}("Common Name ")` The common names of alkyl halides are derived by naming the alkyl group followed by the halide.

`color{green}("IUPAC Name ")` Alkyl halides are named as halosubstituted hydrocarbons in the IUPAC system of nomenclature.

`color{red}("Note ")` Haloarenes are the common as well as IUPAC names of aryl halides.

● For dihalogen derivatives, the prefixes o-, m-, p- are used in common system but in IUPAC system, the numerals 1,2; 1,3 and 1,4 are used.

`=>` The dihaloalkanes having the same type of halogen atoms are named as alkylidene or alkylene dihalides.

● The dihalo-compounds having same type of halogen atoms are further classified as `color{red}("geminal halides")` (halogen atoms are present on the same carbon atom) and `color{red}("vicinal halides")` (halogen atoms are present on the adjacent carbon atoms).

● In common name system, gem-dihalides are named as alkylidene halides.

● In common name system, vic-dihalides are named as alkylene dihalides.

● In IUPAC system, they are named as dihaloalkanes.

Some common examples of halocompounds are mentioned in Table 10.1
Q 2636478372

Draw the structures of all the eight structural isomers that have the molecular formula `C_5H_(11)Br.` Name each isomer according to IUPAC system and classify them as primary, secondary or tertiary bromide.

Solution:

`CH_3CH_2CH_2CH_2CH_2Br \ \ \ \ \ \ text( 1-Bromopentane) (1^0)`
`CH_3CH_2CH_2CH(Br)CH_3 \ \ \ \ \ \ \ text(2-Bromopentane) (2^0)`
`CH_3CH_2CH(Br)CH_2CH_3 \ \ \ \ \ \ \ \ text(3-Bromopentane) (2^0)`
`(CH_3)_2CHCH_2CH_2Br \ \ \ \ \ \ \ \ \ \ \text(1-Bromo-3-methylbutane) (1^0)`
`(CH_3)_2CHCHBrCH_3 \ \ \ \ \ \ \ \ \ \ \ \ \text(2-Bromo-3-methylbutane) (2^0)`
`(CH_3)_2CBrCH_2CH_3 \ \ \ \ \ \ \ \ \ \ \ \ text(2-Bromo-2-methylbutane) (3^0)`
`CH_3CH_2CH(CH_3)CH_2Br \ \ \ \ \ \ \ \ \ \ text(1-Bromo-2-methylbutane) (1^0)`
`(CH_3)_3C CH_2Br \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text(1-Bromo-2,2-dimethylpropane) (1^0)`
Q 2666478375

Write IUPAC names of the following:

Solution:

(i) 4-Bromopent-2-ene (ii) 3-Bromo-2-methylbut-1-ene
(iii) 4-Bromo-3-methylpent-2-ene (iv) 1-Bromo-2-methylbut-2-ene
(v) 1-Bromobut-2-ene (vi) 3-Bromo-2-methylpropene
Q 3241834723

what is difference between geminal halides and vicinal halides ?

Solution:

(1) The di halo- compounds in which halogen atoms are present on the same carbon atom

eg.

* They are also called alkylidene halides .

(2) The di halo- compounds in which halogen atoms are present on the adjacent carbon atoms.

eg.

* They are also called alkylene di halides.
 
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