2. Classification of organic reactions by nature of reagent.

Electrophiles

• electron-deficient species that tend to accept electron(s)

• possess an empty orbital to receive the electron pair

• cations or free radicals seeking electron-rich centres

Nucleophiles

• electron-rich species that tend to seek an electron-deficient site for reaction

• possess lone pairs of electrons

• anions or molecules with lone pairs of electrons

Nature	Electrophile		Nucleophile
	Cation	Free radical	Anion	Molecule with lone pair of electrons
Example	Br+, Cl+, NO2+, R+, RCO+, SO3H+	H•, Br•, Cl•, I•, R•, HO•, CH2=CHCH2•,	Cl–, Br–, I–, RO–, CN–, OH–, RCOO–	H2O, ROH, ROR, NH3, RNH2, R2NH, R3N

2. Classification by the type of organic reactions

Substitution Reactions

An atom or a group of atoms of the reactant molecule is replaced by another atom or group of atoms. Characteristic reactions of saturated compounds

e.g.

H₂O

CH₃ – Cl + NaOH  CH₃ – OH + NaCl

Addition Reactions

Two molecules react to give a single product. Characteristic reactions of compounds with multiple bonds.

e.g.

Elimination Reactions

Atoms or groups of atoms are removed from two adjacent atoms of the reactant molecule. Method for preparing compounds with multiple bonds.

e.g.

Condensation Reactions

Two or more molecules join together, with a small molecule being removed

e.g.

Rearrangement Reactions

A molecule undergoes reorganization of its constituent atoms or groups of atoms

e.g.

2. Classification by number of molecules, which take part in the slowest step of organic reaction (by order reaction)

Second-order reactions are more characteristic for organic chemistry.

e.g.

- first-order nucleophilic substitution reaction;

- second-order radical addition reaction.

2. Isomerism

2.1. Structural Isomerism

Structural Isomers with the Same Functional Group

Chain Isomerism

Chain isomers are isomers that have different carbon skeletons. e.g.

Position Isomerism

Position isomers are isomers that have the same carbon skeleton and functional group. They differ only in the position of the functional group. e.g.

Metamerism

Metamers are those isomers with the functional group interrupting the carbon skeleton at different positions. e.g.

Tautomerism

Tautomers are those isomers with structures differing in arrangement of atoms. They are in dynamic equilibrium with each other. e.g.

Structural Isomers with Different Functional Groups

Functional Group Isomerism

Functional group isomers are isomers that have the same molecular formula but contain different functional groups. e.g.