Phenolic group can be identified by a positive: [2024]
Phthalein dye test
Lucas test
Tollen's test
Carbylamine test
(A)
Phthalein dye test is a test for phenolic group. For example phenol condense with phthalic anhydride in the presence of concentrated to give phenolphthalein which gives a dark pink color with NaOH solution.
Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R:
Assertion A: Aryl halides cannot be prepared by replacement of hydroxyl group of phenol by halogen atom.
Reason R: Phenols react with halogen acids violently.
In the light of the above statements, choose the most appropriate from the options given below: [2024]
A is false but R is true
Both A and R are true and R is the correct explanation of A
A is true but R is false
Both A and R are true but R is NOT the correct explanation of A
(C)
Due to resonance, there is partial double bond character in O-H bond of phenol. This makes the O-H bond difficult to break. Hence it does not react with halogen acids to give aryl halides.
Given below are two statements: One is labelled as Assertion A and the other is labelled as Reason R:
Assertion A: value of phenol is 10.0 while that of ethanol is 15.9.
Reason R: Ethanol is stronger acid than phenol.
In the light of the above statements, choose the correct answer from the options given below: [2024]
A is true but R is false.
Both A and R are true but R is NOT the correct explanation of A.
Both A and R are true and R is the correct explanation of A.
A is false but R is true.
(A)
Phenols are stronger acids than alcohols because phenoxide ion is resonance stabilised whereas there is no resonance in alkoxide ion.
Given below are two statements:
Statement I: Bromination of phenol in solvent with low polarity such as or requires Lewis acid catalyst.
Statement II: The Lewis acid catalyst polarises the bromine to generate .
In the light of the above statements, choose the correct answer from the options given below: [2024]
Statement I is true but Statement II is false.
Both Statement I and Statement II are true.
Both Statement I and Statement II are false.
Statement I is false but Statement II is true.
(D)
The usual halogenation of benzene takes place in the presence of a Lewis acid, such as , which polarises the halogen molecule. In case of phenol, the polarisation of bromine molecule takes place even in the absence of Lewis acid. It is due to the highly activating effect of –OH group attached to the benzene ring, due to which charge density on ring increases and polarization of occurs even in absence of Lewis acid.
