Chapter 1:- Structure and Reactivity

B.sc 1st year Book
Organic Chemistry
(Page 11)

Types of reagents

A chemical reaction is the result of the interaction between two or more than two substances. These are named differently, one being called as “reagent”(the compound that attacks)and the other as“substrate”. 

Substrate + Reagent ⟶ Product

What are electrophilic reagents?

 The reagents are of two types- the one that attacks the positive side of the molecule is called as “nucleophile” or ‘nucleophilic reagent‘.

What are electrophilic reagents?

The reagents are one that attacks the negative side of the molecule is called an “electrophile” or ‘electrophilic reagent‘.

The Reagents are of two types- 

Electrophilic reagents :

A species that can accept a pair of electrons is called as an “electrophilic(electron seeking) reagent’ or Lewis acid. It is because the electrophile seeks an electron-rich (negatively charged)site in a molecule for the attack. It may be a positively charged ion or electron-deficient molecule(a molecule having an atom electron sextet). Some common electrophiles are :

(a) Positively charged ions : H⊕; H3O⊕; X; N⊕O2; S⊕O3H; C6H5N2⊕; C⊕H3; RC⊕H2; R2C⊕H; R2C⊕ etc.

(b) Electron-deficient molecules: BF3; AlX3; SO3; ICl; SnCl2; FeCl3 etc.

Nucleophilic reagents :

A species that can donate a lone pair of electrons is called a nucleophilic(nucleus-seeking) reagent or Lewis base. Nucleophile seeks an electron-deficient site for the attack. It may be a negatively charged or a molecule having an unshared electrons pair or lone pair. Some common nucleophiles are :

(a) Negatively charged ions : HΘ; OΘH; CNΘ; ROΘ; RSΘ; RC≡CΘ; RCOOΘ; NΘH2; CΘH(COOR)3; CΘH3;

(b) Electron-rich molecules: H2O;RO2; NH3; RNH2; R2NH; R3N
; RMgBr; RLi etc. 

Nucleophiles differ from electrophiles as follows-

Nucleophiles  Electrophiles
1. They may be defined as those neutral molecules or anions which contain a donor atom.

2. They have high electron density thus, they attack the substrate at the point of minimum electron density.

3. They have a tendency to donate electron pairs (lone pairs) hence they are considered lewis bases.

4. The reactions involving the attack of nucleophiles are known as nucleophilic reactions.

5. Example: OH–, Br–, CN–, Cl–, NH2, HSO3, COO–, N=C–, OR, ROH, H2O, ROR, RSH, RNH2, NH2, etc

 1. The electrophiles or electrophilic reagents may be defined as those neutral molecules or cations which contain an electron-deficient center.

2. Electrophiles are electron-seeking or electron-loving and thus attack the substrate at the point of maximum electron density.

3. They have a tendency to accept electron pairs (lone pairs) thus, they are lewis acids.

4. The reactions involving the attack of electrophiles are known as electrophilic reactions.

5. Example : H+, Br+, H3O+, NH4+, NO2+, NO+, R–N+≡N, CH
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