You have learnt that substitution of one or more hydrogen atom(s) from a hydrocarbon by another atom or a group of atoms result in the formation of an entirely new compound having altogether different properties and applications. Alcohols and phenols are formed when a hydrogen atom in a hydrocarbon, aliphatic and aromatic respectively, is replaced by –OH group. These classes of compounds find wide applications in industry as well as in day-to-day life. For instance, have you ever noticed that ordinary spirit used for polishing wooden furniture is chiefly a compound containing hydroxyl group, ethanol. The sugar we eat, the cotton used for fabrics, the paper we use for writing, are all made up of compounds containing –OH groups. Just think of life without paper; no note-books, books, newspapers, currency notes, cheques, certificates, etc. The magazines carrying beautiful photographs and interesting stories would disappear from our life. It would have been really a different world. An alcohol contains one or more hydroxyl (OH) group(s) directly attached to carbon atom(s), of an aliphatic system (CH3OH) while a phenol contains –OH group(s) directly attached to carbon atom(s) of an aromatic system (C6H5OH). The subsitution of a hydrogen atom in a hydrocarbon by an alkoxy or aryloxy group
(R–O/Ar–O) yields another class of compounds known as ‘ethers’, for example, CH3OCH3 (dimethyl ether). You may also visualise ethers as compounds formed by substituting the hydrogen atom of hydroxyl group of an alcohol or phenol by an alkyl or aryl group. In this unit, we shall discuss the chemistry of three classes of compounds, namely — alcohols, phenols and ethers.
Mono, Di,Tri or Polyhydric Compounds
Alcohols and phenols may be classified as mono–, di–, tri- or polyhydric compounds depending on whether they contain one, two, three or many hydroxyl groups respectively in their structure.
Ethers
Ethers are classified as simple or symmetrical, if the alkyl or aryl groups attached to the oxygen atom are the same, and mixed or unsymmetrical, if the two groups are different. Diethyl ether, C2H5OC2H5, is a symmetrical ether whereas C2H5OCH3 and C2H5OC6H5 are unsymmetrical ethers.
Excercise
11.1 Explain how does the –OH group attached to a carbon of benzene ring activate it towards electrophilic substitution?
11.2 Write structures of the compounds whose IUPAC names are as follows:
(i) 2-Methylbutan-2-ol (ii) 1-Phenylpropan-2-ol
(iii) 3,5-Dimethylhexane –1, 3, 5-triol (iv) 2,3 – Diethylphenol
(v) 1 – Ethoxypropane (vi) 2-Ethoxy-3-methylpentane
(vii) Cyclohexylmethanol (viii) 3-Cyclohexylpentan-3-ol
(ix) Cyclopent-3-en-1-ol (x) 3-Chloromethylpentan-1-ol.
11.3 (i) Draw the structures of all isomeric alcohols of molecular formula C5H12O and give their IUPAC names.
(ii) Classify the isomers of alcohols in question 11.3 (i) as primary, secondary and tertiary alcohols.
11.4 Explain why propanol has higher boiling point than that of the hydrocarbon, butane?
11.5 Alcohols are comparatively more soluble in water than hydrocarbons of comparable molecular masses. Explain this fact.
11.6 What is meant by hydroboration-oxidation reaction? Illustrate it with an example.
11.7 Give the structures and IUPAC names of monohydric phenols of molecular formula, C7H8O.
11.8 While separating a mixture of ortho and para nitrophenols by steam distillation, name the isomer which will be steam volatile. Give reason.
11.9 Give the equations of reactions for the preparation of phenol from cumene.
11.10 Write chemical reaction for the preparation of phenol from chlorobenzene.
11.11 Write the mechanism of hydration of ethene to yield ethanol.
11.12 You are given benzene, conc. H2SO4 and NaOH. Write the equations for the preparation of phenol using these reagents.
11.13 Show how will you synthesise:
(i) 1-phenylethanol from a suitable alkene.
(ii) cyclohexylmethanol using an alkyl halide by an SN2 reaction.
(iii) pentan-1-ol using a suitable alkyl halide?
11.14 Give two reactions that show the acidic nature of phenol. Compare acidity of phenol with that of ethanol.
11.15 Explain why is ortho nitrophenol more acidic than ortho methoxyphenol ?
Please refer to attached file for NCERT Class 12 Chemistry The Solid State
