Q15.52 P - Chemistry: Molecular Nature Of Matter And Change

Question

Of the three significant organic reactions, which do not occur readily with benzene? Why?

Step-by-Step Solution

Answer

Benzene does not undergo addition reach and only shows electrophilic substitution and elimination reactions.

Step 1: Organic reactions

There are three major types of organic reactions:

1. Electrophilic substitution reaction: Reaction in which atom attached to ring is replaced by the electrophile.
2. Elimination reaction: The atom attached to the ring is removed, and an unsaturated bond is formed.
3. Addition reaction: the reaction in which electrophile is added to the aromatic ring.

Step 2: Benzene electrophilic substitution reaction

Benzene has a pi-electron and shows delocalisation of electrons so that the ring is highly electron-rich and attracts the electron-deficient atom. This is called electrophile hence e, shows n electrophilic substitution reaction as shown below:

                                          Benzene electrophile substitution 

Step 3: Benzene elimination reaction

Benzene does not show an elimination reaction because it destroys the ability of benzene, but substituted benzene shows elimination tobenzeneenzyne, which is an unstable intermediate because benzene loses its aromaticity, as shown:

Step 4: Benzene addition reaction

Benzene resists addition reactions because pi-electron’s delocalisation in the ring benzene is highly stable due to its aromatic character. With the addition of an electrophile, its aromaticity break the delocalisation of electrons gets disturbed, so it doesn’t show an addition reaction.

Resonance form of benzene