What do you mean by:
(i) Elimination reactions
(ii) Rearrangement reactions?

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(i) Elimination reactions: An elimination reaction is one which involves the loss of two atoms or groups either from the same or adjacent atoms of a substance leading to the formation of multiple bond i.e. double or triple bond. In such reactions at least two σ; bonds are lost and one ; bond is created. These are two types:
(a) β-elimination reaction. Here loss of two atoms or groups takes place from the adjacent carbon atoms in the molecule. For example,

(i) Dehydrohalogenation of alkyl halides with an alcoholic solution of KOH.



(ii) Dehydration of alcohols in the presence of concentrated H₂SO₄ upon heating:



(iii)  -Elimination reactions. In such reactions, there is loss or elimination of two atoms or groups from the same carbon atom in the molecule. For example.

(b) Dehydrohalogenation of chloroform with NaOH



(ii) Dehydrogenation of primary or secondary alcohols with reduced copper at 573K.



(iii) Rearrangement reactions Reactions involving the shift or migration of an atom or a group from one atom to another within the same molecule are called rearrangement reactions for example.
 (i) n-Butane rearranges to form 2-methyl propane when heated in a sealed tube in the presence of AlCl₃/HCl.





(ii) Ammonium cyanate upon heating rearranges to form urea.


  

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(i) Isomerisation reaction. All those reactions in which interconversion of isomers take place without affecting the molecular formulae and carbon skeletons of reactants and products are called Isomerisation reactions. For example,



(ii) Condensation reaction. All those reactions in which two same or different organic reactants unite to give a product with or without the elimination of another, simple molecule are called condensation reaction. For example condensation of aldehyde or ketone.

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(i) Substitution reactions. In a substitution reaction, a group or radical attached to a carbon atom is removed and another one enters in its place; no change in the degree of unsaturation or structure of the substance occurs.
The product is called substitution product. For example. 



The substitution reactions are further classified into three types depending upon the nature of the attacking reagent. 

(a) Electrophilic substitution reaction (S_E reactions):
In these reactions, the attacking reagent is an electrophile. For example,



(b) Nucleophilic substitution reactions (S_N reactions₎: 

Substitution reactions which are brought about by nucleophiles are called nucleophilic substitution reactions.



(c) Free radical substitution reactions. Substitution reactions brought about by free radicals are called free radical substitution reactions. Such reactions are carried either at high temperature or in the presence of ultraviolet light. For example, chlorination of methane to form chloromethane consists of the following three fundamental steps:

(a) Initiation:


(ii) Addition reactions. Reactions which involve combination between two reacting molecules to yield a single molecule of the product are called addition reactions. This addition occurs at the carbon atoms joined by a double or triple bond, leading to change in the degree of unsaturation of the molecule and the molecule becomes nearly saturated.



Addition reactions are of three types depending upon the nature of attacking reagent. 

(a) Electrophilic addition reactions. Addition reactions brought about by electrophiles are called electrophilic addition reactions. For example the addition of bromine or HBr to ethylene. 


(b) Nucleophilic addition reactions. Addition reactions brought about by nucleophiles are called nucleophilic addition reactions. For example, the addition of HCN to aldehydes.



(c) Free radical addition reactions. Addition reactions brought about by free radicals are called free radical addition reactions. For example, the addition of HBr to alkenes in the presence of peroxides.


This reaction takes place as follows:
Initiation:

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Fractional distillation: This process is generally used for those mixtures, where the difference in the boiling points of the two liquids is less than 15 K. Acetone boils at 330 K while methyl alcohol at 338 K, therefore, these two liquids are separated by the fractional distillation process. This is similar to the ordinary distillation method with the only exception that a fractionating column is introduced in between the distillation flask and the condenser.
The process of separation of the components of a liquid mixture at their respective boiling points in the form of vapours and the subsequent condensation of these vapours is called fractional distillation.

The fractionating columns used for the purpose are of different shapes as shown in the figure.

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Simple distillation: The process of converting an organic liquid to its vapours and then condensing the vapours to its pure form in the liquid state is called distillation. This technique is applied:

(i) to purify a liquid containing a non-volatile miscible impurity say benzene and benzophenone.

(ii) for the separation of two liquids having boiling point difference more than about 313 K.
The impure liquid is taken in a distillating flask and apparatus is arranged as shown. The liquid is heated, when it vapourises. These vapours are condensed and the pure liquid is collected in the receiver. The impurities remain in the flask.