- How are free radicals and electrophiles formed ?
- why is phenol acidic but alcohol is not in terms of resonance
Answer 1-
Formation of free radicals-
(i) Dissociation of chlorine gas in the presence of ultra violet light produces chlorine free radicals:
(ii) Alkyl free radical may be obtained when free radical chlorine attacks alkanes.
Formation of electrophile: Electrophile is an electron deficient species. Electrophiles are formed by heterolytic fission of a bond. For example: Heterolytic fission of methyl bromide gives carbocation, which is an electrophile.
Answer 2-
The hydroxyl group in phenol is directly attached to the sp2 hybridised carbon of benzene ring which acts as an electron withdrawing group. Due to the higher electronegativity of sp2 hybridised carbon of the phenol to which -OH is attached, electron density on oxygen decreases. This increases the polarity of O-H bond and results in an increase in ionisation of phenols. As a result H+ ion can be easily released from aqueous solution. Also the phenoxide ion is resonance stabilised.
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In case of alcohols, there is no such stability of alkoxide ion.
R-O-H ⇌ R-O- + H+
Formation of free radicals-
(i) Dissociation of chlorine gas in the presence of ultra violet light produces chlorine free radicals:
(ii) Alkyl free radical may be obtained when free radical chlorine attacks alkanes.
Formation of electrophile: Electrophile is an electron deficient species. Electrophiles are formed by heterolytic fission of a bond. For example: Heterolytic fission of methyl bromide gives carbocation, which is an electrophile.
Answer 2-
The hydroxyl group in phenol is directly attached to the sp2 hybridised carbon of benzene ring which acts as an electron withdrawing group. Due to the higher electronegativity of sp2 hybridised carbon of the phenol to which -OH is attached, electron density on oxygen decreases. This increases the polarity of O-H bond and results in an increase in ionisation of phenols. As a result H+ ion can be easily released from aqueous solution. Also the phenoxide ion is resonance stabilised.
In case of alcohols, there is no such stability of alkoxide ion.
R-O-H ⇌ R-O- + H+