Classification and Nomenclature of Haloalkanes Class 12 Notes | EduRev

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Class 12 : Classification and Nomenclature of Haloalkanes Class 12 Notes | EduRev

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1.1 Aliphatic halogen derivatives:

Compounds obtained by the replacement of one or more hydrogen atom(s) from hydrocarbons are known as halogen derivatives. The halogen derivatives of alkanes, alkenes, alkynes and arenes are known as alkyl halide (haloalkene), alkenyl halide (haloalkenes), alkynyl halides (haloalkynes) and aryl halides (halobenzenes) respectively.

Alkyl halides: Monohalogen derivatives of alkanes are known as alkyl halides.

Structure of alkyl halides: 

Classification and Nomenclature of Haloalkanes Class 12 Notes | EduRev

Classification of alkyl halides: 

(i) Primary halide: If the halogen bearing carbon is bonded to one carbon atom or with no carbon atom.

Example: 

CH3 - X, R - CH2 - X

(ii) Secondary halide: If two carbon atoms are bonded to the halogen bearing carbon atom.

Example: 

Classification and Nomenclature of Haloalkanes Class 12 Notes | EduRev  Classification and Nomenclature of Haloalkanes Class 12 Notes | EduRev

(ii) Tertiary halide: Three other carbon atoms bonded to the halogen bearing carbon atom.

Example: 

Classification and Nomenclature of Haloalkanes Class 12 Notes | EduRev , Classification and Nomenclature of Haloalkanes Class 12 Notes | EduRev

Halolkanes can be classified into following three categories.

(i) Monohaloalkanes (ii) Dihaloalkanes (iii) Polyhaloalkanes

1.2 IUPAC Nomenclature of alkyl halides 

S.N.
Compound
IUPAC name
1
Classification and Nomenclature of Haloalkanes Class 12 Notes | EduRev
2 – Chloro-2-methylpropane
2
Classification and Nomenclature of Haloalkanes Class 12 Notes | EduRev
3-Bromo-1-chlorobutane
3
Classification and Nomenclature of Haloalkanes Class 12 Notes | EduRev
2-Bromo-1-chloro-4-fluoro-3-methylbutane
4
Classification and Nomenclature of Haloalkanes Class 12 Notes | EduRev
2-Bromo-1-chloro-3-iodocyclopentane
5
Classification and Nomenclature of Haloalkanes Class 12 Notes | EduRev
5-chloropentan-2-ol
6
Classification and Nomenclature of Haloalkanes Class 12 Notes | EduRev
5-Fluoropent-1-ene
7
Classification and Nomenclature of Haloalkanes Class 12 Notes | EduRev
Chlorophenylmethane
8
Classification and Nomenclature of Haloalkanes Class 12 Notes | EduRev
Dichlorophenylmethane
9
Classification and Nomenclature of Haloalkanes Class 12 Notes | EduRev
Trichlorophenylmethane
10
Classification and Nomenclature of Haloalkanes Class 12 Notes | EduRev
2,2-Bis(chloromethyl)-1,3-dichloropropane
11
Classification and Nomenclature of Haloalkanes Class 12 Notes | EduRev
Cis-1,4-dibromocyclohexane
12
Classification and Nomenclature of Haloalkanes Class 12 Notes | EduRev
2-iodo-3-phenylbutane

 

1.3 Isomerism in Haloalkanes 

1. Structural Isomerism: 

(a) Chain

IUPAC name - 

1. Classification and Nomenclature of Haloalkanes Class 12 Notes | EduRev

2. Classification and Nomenclature of Haloalkanes Class 12 Notes | EduRev

(b) Position

Classification and Nomenclature of Haloalkanes Class 12 Notes | EduRev

Classification and Nomenclature of Haloalkanes Class 12 Notes | EduRev

2. Stereoisomerism 

(a) Optical isomerism

Classification and Nomenclature of Haloalkanes Class 12 Notes | EduRev

Classification and Nomenclature of Haloalkanes Class 12 Notes | EduRev

Classification and Nomenclature of Haloalkanes Class 12 Notes | EduRev

1.4 Bonding in alkyl halide: 

Table : 1 Carbon halogen bond lengths

Classification and Nomenclature of Haloalkanes Class 12 Notes | EduRev

Ex.1 Classify the compound as a primary, secondary and tertiary halide. 

(a) (CH3)2CH-CH2Cl

(b) Classification and Nomenclature of Haloalkanes Class 12 Notes | EduRev

(c) Classification and Nomenclature of Haloalkanes Class 12 Notes | EduRev

(d) Classification and Nomenclature of Haloalkanes Class 12 Notes | EduRev

(e) Isopentyl bromide

(f) Neopentyl iodide

Sol. (a) Primary

(b) Secondary

(c) Tertiary

(d) Primary

(e) Primary

(f) Primary

1.5 Physical properties of alkyl halides: 

1.5.1 Dipole moment of the halogen derivatives:

m = 4.8 × δ × d

Where δ is the charge and d is the bond length

These two effects e.g. charge and distance oppose each other, with the larger halogens having longer bond but weaker electronegativity. The overall result is that the bond dipole moment increase in the order.

C - I  < C - Br  < C - F < C - Cl

μ : 1.29 D 1.48 D  1.51 D     1.56 D

The electronegativities of the halogen increase in the order:

I < Br < Cl < F

Table: 2 Molecular dipole moments of methylhalides

Classification and Nomenclature of Haloalkanes Class 12 Notes | EduRev

1.5.2 Boiling point: 

(a) With respect to the halogen in a group of alkyl halides, the boiling point increases as one descends the periodic table. Alkyl fluorides have the lowest boiling points and alkyl iodides have the highest boiling point. This trend matches the order of increasing polarizability of the halogens. (Polarizability is the ease with which the electrons distribution around an atom is distorted by a nearby electric field and is a significant factor in determining the strength of induced-dipole/induced-dipole and dipole/induced-dipole attractions). Forces that depend on induced dipoles are strongest when the halogen is a highly polarizable iodine, and weakest when the halogen is a nonpolarizable fluorine.

Table: 3 Boiling points of some alkyl halide in ºC (1 atm)

Classification and Nomenclature of Haloalkanes Class 12 Notes | EduRev

Fluorine is unique among the halogens is that increasing the number of fluorine does not lead to higher and higher boiling point.

(b) The boiling points of the chlorinated derivatives of methane increase with the number of chlorine atoms because of an increase in the induced-dipole/dipole attractive forces.

Compound:

CH3Cl

CH2Cl2

CHCl3

CCl4

B.P.

-24ºC

40ºC

61ºC

77ºC

Table: 4 

Classification and Nomenclature of Haloalkanes Class 12 Notes | EduRev

1.5.3 Density: 

Alkyl fluorides and chlorides are less dense and alkyl bromides and iodides more dense than water.

Table: 5

Classification and Nomenclature of Haloalkanes Class 12 Notes | EduRev

Because alkyl halides are insoluble in water, mixture of an alkyl halide and water separates into two layers. When the alkyl halides have a fluoride or chloride, then alkyl halides is on the upper layer and water is the lower. The situation is reversed when the alkyl halide is a bromide or an iodide. In these cases the alkyl halide is in the lower layer. Polyhalogenation increases the density. The compounds CH2Cl2 CHCl3 and CCl4, for example, are all more dense than water.

1.6 Preparation of alkyl halide: 

 1.6.1 From alkane : 

R - H Classification and Nomenclature of Haloalkanes Class 12 Notes | EduRev R - X HX

1.6.2 From alkenes and alkynes (Detail in alkene and alkyne) 

(a) Classification and Nomenclature of Haloalkanes Class 12 Notes | EduRev

(b) Classification and Nomenclature of Haloalkanes Class 12 Notes | EduRev

(c) Classification and Nomenclature of Haloalkanes Class 12 Notes | EduRev

(d) Classification and Nomenclature of Haloalkanes Class 12 Notes | EduRev

 

1.6.3 From alcohol (Detail in the alcohol) 

R - OH Classification and Nomenclature of Haloalkanes Class 12 Notes | EduRev R - X

1.6.4 From other halides 

R - X I-Classification and Nomenclature of Haloalkanes Class 12 Notes | EduRev R - I X-

R - Cl KF Classification and Nomenclature of Haloalkanes Class 12 Notes | EduRev R - F

Finkelstein Reaction 

1. CH- CH2 - Cl Classification and Nomenclature of Haloalkanes Class 12 Notes | EduRev CH3 - CH2 - I

Nucleophility - in Polar Protic solvent - F< Cl<Br<I-

Polar Aprotic solvent - F> Cl>Br> I-

Covalent Nature : NaF < NaCl < NaBr < NaI

Classification and Nomenclature of Haloalkanes Class 12 Notes | EduRev

Acetone → acetone is soluble.

NaF < NaCl < NaBr < NaI

2. C - C - Br Classification and Nomenclature of Haloalkanes Class 12 Notes | EduRev C - C - Br

3. C - C - Cl Classification and Nomenclature of Haloalkanes Class 12 Notes | EduRev C - C - Cl

4. C - C - Cl Classification and Nomenclature of Haloalkanes Class 12 Notes | EduRev C - C - F

5. C - C - Cl Classification and Nomenclature of Haloalkanes Class 12 Notes | EduRev C - C - F (Swart's reaction)

6. Classification and Nomenclature of Haloalkanes Class 12 Notes | EduRev

7. Classification and Nomenclature of Haloalkanes Class 12 Notes | EduRev (racemisation)

 

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