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