What traumatic event does Zitkala-Sa describe at the school?

The forcible cutting of her long hair

Why was the cutting of her hair so humiliating to Zitkala-Sa?

Among her people, shingled hair was worn by cowards and mourners

Why are alcohols more soluble in water than the corresponding hydrocarbons?

They form hydrogen bonds with water through their -OH group.

Why is phenol more acidic than ethanol?

The phenoxide ion is stabilised by resonance over the benzene ring, while the ethoxide ion is not.

How are alcohols classified?

As primary, secondary or tertiary depending on whether the -OH carbon is bonded to one, two or three other carbons.

What is the Williamson ether synthesis?

An alkyl halide reacts with a sodium alkoxide or aryloxide by \(S_N2\) to give an ether.

What happens when a primary alcohol is oxidised?

It is oxidised first to an aldehyde and then to a carboxylic acid.

Why does the -OH group activate the benzene ring in phenol?

The lone pairs on oxygen are donated into the ring by resonance, increasing electron density at ortho and para positions.

What is the product of dehydration of ethanol with hot concentrated H\(_2\)SO\(_4\)?

Ethene, by elimination of a water molecule.

How is phenol prepared from cumene?

Cumene is oxidised to cumene hydroperoxide, which on acid treatment gives phenol and acetone.

Why are ethers relatively unreactive?

The C-O bonds are strong and there is no easily attacked functional centre, though strong acids can cleave them.

What is Lucas reagent used for?

A mixture of concentrated HCl and ZnCl\(_2\) used to distinguish primary, secondary and tertiary alcohols by reaction rate.

Alcohols, Phenols and Ethers

Class 12 Chemistry · Chemistry Part II · Chapter 2

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CBSE Class 12 · Chemistry

Unit 8 carbonyls: 8 marks, biggest unit

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Summary

Alcohols and phenols are formed when a hydrogen atom of an aliphatic or aromatic hydrocarbon respectively is replaced by a hydroxyl (-OH) group, while ethers have an oxygen atom linking two alkyl or aryl groups. Alcohols are classified as primary, secondary or tertiary depending on the carbon bearing the -OH group, and are named by the IUPAC system. They are prepared by hydration of alkenes, reduction of aldehydes, ketones and carboxylic acids, and from Grignard reagents. Phenols are prepared from haloarenes, benzenesulphonic acids, diazonium salts and cumene. Alcohols and phenols show hydrogen bonding, which raises their boiling points and water solubility. Chemically alcohols react at the O-H bond (showing weak acidity and ester formation) and the C-O bond (substitution and dehydration to alkenes), and undergo oxidation. Phenols are more acidic than alcohols because the phenoxide ion is stabilised by resonance, and the -OH group activates the ring toward electrophilic substitution at ortho and para positions. Ethers are prepared by dehydration of alcohols and by the Williamson synthesis from alkyl halides and sodium alkoxides; they are relatively unreactive but the C-O bond can be cleaved by hydrogen halides. These compounds are widely used as solvents, antiseptics, fragrances and fuels.

Classification and IUPAC nomenclaturePreparation of alcohols, phenols and ethersPhysical properties and hydrogen bondingReactions of alcohols (acidity, esterification, oxidation)Acidity and reactions of phenolsEthers: Williamson synthesis and reactions

Key terms

Alcohol

A compound with a hydroxyl group attached to an \(sp^3\) carbon of an alkyl chain.

Phenol

A compound with a hydroxyl group attached directly to an aromatic ring.

Ether

A compound in which an oxygen atom is bonded to two alkyl or aryl groups.

Williamson synthesis

Preparation of an ether from an alkyl halide and a sodium alkoxide or aryloxide.

Esterification

Reaction of an alcohol with a carboxylic acid to form an ester and water.

Phenoxide ion

The conjugate base of phenol, stabilised by resonance, accounting for phenol's acidity.

Extra questions & answers

Try one from this chapter

A phenol has a hydroxyl group attached to:

Flashcards & interactive practice