Chemistry NCERT Exemplar Solutions Class 12th Chapter Eleven

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When benzene diazonium chloride is heated with water, it forms phenol along with nitrogen and hydrochloric acid as by-products as shown below:

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The decreasing order of reactivity of alcohol with sodium metal:

Tertiary Alcohols > Secondary Alcohols   > Primary Alcohols 

When alcohol reacts with active metals  e.g. Na. K etc., the O-H bond of alcohols breaks to form the corresponding alkoxide. The alkyl  group is electron donating and has +I effect due to which the O-H bond becomes strong and hence, the reactivity of alcohol decreases.

Fig: +I effect of alkyl group of alcohol

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The increasing order of acidity:

o-cresol  <  Phenol   <  o-nitrophenol

The electron-withdrawing group on the substituted phenol increases the acidity due to increasing the polarity of the O-H bond and thus, the acidity increases  and vice versa. -NO₂ is an electron-withdrawing group whereas the -CH₃ group is an electron-donating group.

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Out of o-nitrophenol and o-cresol, o-nitrophenol  is more acidic due to the -I effect and -R effect of -NO₂ group as the -NO₂ group is an electron withdrawing group whereas the -CH₃ group is electron releasing group and has +I effect on the conjugate base which increases the electron density and decreases the polarity of O-H bond and hence less acidic.

Fig: The -I effect of NO₂ group and + I effect of CH₃ group on the polarity of O-H bond

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Out of o-nitrophenol and p-nitrophenol, o-nitrophenol is more volatile due to presence of intramolecular hydrogen bonding in o-nitrophenol whereas p-nitrophenol has intermolecular hydrogen bonding.

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The strong oxidising agents such as acidified KMnO₄ or  K₂Cr₂O₇ reagents are used for the conversion of ethanol to ethanoic acid. These reagents are so strong that they convert the alcohols to carboxylic acids.

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The reagent used for the conversion of ethanol to ethanal is pyridinium chlorochromate (PCC) which is a complex formed by CrO₃, pyridine and HCl which converts the primary alcohols to aldehydes.

CH₃—CH₂—OH CH₃—CHO

Ethanol                                   Ethanal

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2-chloroethanol is more acidic than ethanol  because the conjugate base  of  2-chloroethanol   is more stable than that of ethanol due to the -I effect of chlorine atom.

Stability:   Cl—CH₂—CH₂—OΘ           >                     CH₃—CH₂—OΘ

Acidity:     Cl—CH₂—CH₂—OH   >                     CH₃—CH₂—OH

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The reagent pyridinium chlorochromate (PCC) is a complex formed by CrO₃, pyridine and HCl converts the secondary alcohol to ketone without oxidising the double bond.