91Ó°ÊÓ

If there is a bulkier base, elimination will occur. The base here is more bulkier to give elimination not substitution. This is E2 elimination as the reactant is primary bromide and primary carbocation are not stable.

There is primary alkyl halide, so SN² will be. It second ordernucleophilic substitution. The base or nucleophile attached to the opposite site of chlorine and remove the chlorine and change the configuration of the compound take place.

Here the nucleophile, attack from the backside of bromine group and remove bromine. Here the configuration will be changed. As this is primary bromide then here SN ²will occur.

Here the cyanide group attacks the carbon and remove the iodine. Here also the configuration of the central carbon will be changed. In one step CN^-nucluophile attached to carbon to leave I^- in SN² path.

The chlorine leaving group will be removed by the addition of sodium iodide nucleophile. The iodide will be attached to the carbon. There also be a change in configuration. There is no way of SN1 as the chloride is a primary.halide.

In presence of 18- crown ether and methyl cyanide potassium fluoride acts as base..

The chlorine is removed when the cyanide group is attached to the carbon. This primary halide so there is no possibility of SN1. There is a change in configuration in this.