NEET Chemistry Notes Some Basic Principles and Techniques -Types of Organic Reactions
Types of Organic Reactions
Types of Organic Reactions
Based on the nature of reactants, products and byproducts as well as the mechanism, organic reactions are classified into four major categories, substitution, addition, elimination and rearrangement reactions.
- Substitution Reactions
A substitution reaction is a type of reaction in which one atom, or a group of atoms, from the reagent replaces or substitutes itself for one atom or a group of atoms on the substrate.
• In a nucleophilic substitution, the reagent is a nucleophile (base). In an electrophilic substitution, the reagent is an electrophile (acid), e.g.
- Addition Reactions
In an addition reaction, atoms or groups of atoms from the reagent add to the substrate generally without loosing any atomg^gin the substrate. Thus, the product gains atoms from the reagent without loosing any atoms from the^aotetrate.
- Elimination Reactions
An elimination reaction removes two atoms or two groups of atoms from the substrate, giving the product a multiple bond or, in some cases, causing it to form a ring.
- Rearrangement Reactions
In rearrangement reactions, only bonding pattern of reactant changes. Rearrangement reactions usually occur in the presence of a catalyst or under special thermodynamic conditions.
Methods of Purification of Organic Compounds
The common techniques used for the purification are as follows :
Some solid substances directly changes into vapour phase. This process is known as sublimation. Sublimation is used to separate sublimable compounds from non-sublimable compounds.
This is one of the most commonly used technique for the purification of solid organic compounds. It is based on tn6 difference in the solubilities of the compound and the Imphrities in a suitable solvent.
This method is used to separate
- volatile liquids from non-volatile impurities.
- the liquids having sufficient difference in their boiling points. Liquids having different boiling points vaporise at different temperatures (fractional distillation)
- Distillation under reduced pressure This method is used to purify liquids having very high boiling points and those, which decompose at or below their boiling points. Glycerol can be separated from spent lye in soap industry by this method.
- Steam distillatioh This method is used when substances are steam volatile and immiscible with water.
- In steam distillation, steam from a steam generator is passed through a heated flask containing the liquid to be distilled. The mixture of steam and the volatile organic compound, so obtained is condensed and collected. The compound is later separated from water using a separating funnel.
- Aniline, nitrobenzene, sandal wood oil, bromobenzene, o-nitrophenol, o-hydroxy acetophenone are obtained or purified by this method.
When an organic compound is present in aqueous medium, it is separated by shaking it with an organic solvent, in which it is more soluble than in water.
The organic solvent and the aqueous solution should be immiscible with each other so that they form two distinct layers which can be, separated by separating funnel.