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CBSE Class 12 Chemistry Alcohol Phenol Ether Exam Notes. Please refer to the examination notes which you can use for preparing and revising for exams. These notes will help you to revise the concepts quickly and get good marks.
Q1.Arrange the following compounds increasing order of boiling point pentanol, butanol, butan 2- ol, propan-1-ol, methanol
Ans.Methanol < ethanol < propanol < butan 2-ol (branch) < butanol < pentanol. B.P is directly related to moleculer mass and indirectly to branching.
Q2.Arrange the following in the increasing order of property given:
(a)CH3CH2OH, CF3CH2OH, CCl3CH2OH –– Acid strength.
(b)2 methyl-2-propanol, 1 butanol and 2-butanol-reactvity towards Na.
Ans.(a) Due to – I effect of the halogen the O – H bonds weakens and release of a proton. F is more electronegative than Cl.
(b)Reactivity depends on strength of Acidity of Alcohols with Na 1 butanol > 2-butanol > 2 methyl - 2 - propanol (+I effect)
Q3.Unlike phenols, alcohols are easily protonated.
Ans.Due to resonance, the lone pairs of electrons on O atoms are delocatised over the benzene ring while in alcohols, they are easily available for protonation.
Q4.How do you account for the fact that unlike phenol, 2, 4 dinitro phenol and 2, 4, 6 - trinitrophenol are soluble in Na2CO3 (aq) solution.
Ans.Presence of 2 NO2 and 3 NO2 (strong EWG) in above nitro compound which makes them more acidic and will easily soluble in Na2CO3.
Q5.Alcohols react with halogen acid or phosphorous halides to form haloalkanes but phenol does not form halobenzene.
Ans. aliphatic alcohol carbon atom has sp3 hybridisation, Phenol has sp2 hydridisation at C – OH bond which is also get double boud character by resonance. So it cannot give Nucleophilic substitution reactions.
Q6.Explain why dehydration of alcohols to form alkenes is always carried out with conc. H2SO4 and not with conc. HCl or HNO3.
Ans.Reaction with acid will give carbocation. In case HSO4 – being non-nucleophile cannot substitute the Halogen group but in case Cl– will give substition rx. in presence of HNO3 as NO3- is a nucleophile. HCl being oxidising agent, and oxidise alcohol to aldehyde then to acid.
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