(a) How do you convert the following?

(i) Phenol to benzene

(ii) Ethanol to ethane

(b) Give the chemical tests to distinguish between the following pairs of compounds:

(i) Ethanol and phenol

(ii) Butan-2-ol and 2-methylpropan-2-ol

(c) Write the IUPAC name of

OR

(a) Write the mechanism for the preparation of alcohols from alkenes (acid catalysed hydration).

(b) Give reasons for the following:

(i) Phenols do not undergo substitution of the –OH group, like alcohols.

(ii) p-nitrophenol is more acidic than p-methylphenol.

(a) (i) Phenol on strong heating with zinc dust gives benzene

(ii) Ethanol in presence of acid undergoes dehydration to give ethene.

Ethane on reduction with nickel gives ethane.

(b) (i) Iodoform test and bromine water test can be used to distinguish between ethanol and phenol.

Ethanol reacts with iodine in presence of sodium hydroxide to give yellow precipitate of Iodoform while phenol react.

Phenol reacts with bromine water to give a white precipitate of tribromophenol while ethanol does not react.

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(ii) Lucas test can be used to distinguish between Butan-2-ol and 2-methylpropan-2-ol. Butan-2-ol is a secondary alcohol while 2-methylpropan-2-ol is a tertiary alcohol. When a solution of ZnCl₂ and conc.HCl is added to Butan-2-ol turbidity appears after 5 minutes

ile 2-methylpropan-2-ol gives immediate turbidity, due to formation of alkyl halide.

(c) 2-methylpropan-2-ol

The longest possible chain in this is 3 membered, hence the parent name ‘propan’ and the second carbon is substituted with methyl and alcohol.

OR

(a) Water in presence of acid reacts with alkenes to give alcohols.

Step 1: The electrophile H₃O⁺ is attacked by the alkene to form carbocation.

Step 2: Nucleophilic attack by water molecule on carbocation

Step 3: Loss of proton to form alcohol

(b) (i) Phenols do not undergo substitution of the –OH group, like alcohols, as the bond between carbon and oxygen in phenol is a partial double bond as 3 out of the 5 resonance structures shows double bonds.

It is difficult for a nucleophile to break wo bonds, while in alcohols the bond between carbon and oxygen is single, hence phenol does not undergo –OH reactions like alcohols.

(ii) Phenol is benzene ring with –OH group. In p-nitrophenol there is a nitro(-NO₂) group on 4^th carbon, which is electron withdrawing in nature(-R) while in p-methylphenol there is methyl(-CH₃) on 4^th carbon, which is electron releasing (+R) in nature. +R effect increases the electronegativity on oxygen in –OH group thereby making the oxygen to hold on to hydrogen, decreasing its acidity. While in p-nitrophenol the nitro group pulls the electron density towards itself creating delta positive charge on oxygen. Positive charge on oxygen is not stable, so it readily loses the proton making it more acidic.