There are two types of resonance effect:
1) Positive resonance effect: In this effect the transfer of electrons is away from an atom or substituent group attached to the conjugated system. The atoms or groups which shows + R effect are halogens,-OH,-OR,-
NH2
2) Negative resonance effect: In this effect the transfer of electrons is towards the atom or substituent group attached to the conjugated system.
The atoms or groups which shows-R effect are – COOH,-CHO,-CN METHODS OF PURIFICATION OF ORGANIC COMPOUNDS:
Sublimation: This method is used to separate the sublimable compounds from non sublimable compounds.
Crystallization: This method is based on the difference in the solubilities of compound and impurities in a suitable solvent. The impure compound is dissolved in solvent at heated at higher temp. on cooling the hot and conc solution pure compounds crystallizes out.
Distillation: This method is used to separate volatile liquids from non volatile liquids and liquids having sufficient difference in their boiling points.
Fractional distillation: If the boiling points of two liquids is not much, they are separated by this method.
Distillation under reduced pressure: This method is used to purify liquids having high boiling points and decomposes at or below their boiling points.
Steam distillation: This method is used to separate substances which are steam volatile and are immiscible with water.
Differential Extraction: When an organic compound is present in an aqueous medium it is separated by shaking it with organic solvent in which it is more soluble than in water. The aqueous solution is mixed with organic solvent in a separating funnel and shaken for sometimes and then allowed to stand for some time. when organic solvent and water form two separate layers the lower layer is run out by opening the tap of funnel and organic