Chemistry Classification and Nomenclature of Haloalkanes and Haloarenes

### 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.