Alcohols, Phenols and Ethers: common doubts, answered
The questions students ask most often about Alcohols, Phenols and Ethers, each with a short answer. For the full chapter, read the Alcohols, Phenols and Ethers notes.
About the chapter
How is Alcohols, Phenols and Ethers usually tested in NEET?
Expect acidity order questions comparing alcohols, water and substituted phenols, and named reactions such as Kolbe, Reimer-Tiemann, Williamson and the cumene process. Reagent questions cover PCC, the Lucas test, hydroboration and ether cleavage with HI. Conversion chains that combine Grignard reagents with oxidation steps are common, so practise identifying the alcohol class each one produces.
Classification
Read this section in the notes →Is benzyl alcohol a phenol?
No. In benzyl alcohol, C₆H₅CH₂OH, the –OH is attached to an sp³ CH₂ carbon outside the ring, so it is a primary alcohol and behaves like one. A phenol has the –OH bonded directly to an sp² carbon of the aromatic ring. That direct attachment is what gives phenols their greater acidity and their activated ring.
Nomenclature and structure
Read this section in the notes →Why is the C–O–H bond angle in methanol slightly less than the tetrahedral angle?
The oxygen in methanol is sp³ hybridised, but its two lone pairs repel the bonding pairs more strongly than bonding pairs repel each other. This squeezes the C–O–H angle to about 108.9°, a little below 109.5°. In phenol the C–O bond is shorter than in methanol, because the oxygen's lone pair is partly shared with the ring.
Preparing alcohols
Read this section in the notes →Why does hydroboration-oxidation of propene give propan-1-ol and not propan-2-ol?
Diborane adds to the double bond so that boron attaches to the end carbon, which is less hindered, and hydrogen to the middle one. Oxidation with alkaline hydrogen peroxide then replaces boron with –OH, so the –OH ends up on the terminal carbon. The overall result is anti-Markovnikov, unlike acid-catalysed hydration, which gives propan-2-ol.
Which type of alcohol do Grignard reagents give with methanal, other aldehydes and ketones?
The Grignard reagent adds its alkyl group to the carbonyl carbon, and hydrolysis then gives an alcohol. Methanal, HCHO, has two hydrogens on that carbon, so it gives a primary alcohol. Any other aldehyde has one hydrogen and one alkyl group, so it gives a secondary alcohol. A ketone has two alkyl groups, so it gives a tertiary alcohol.
Preparing phenols
Read this section in the notes →How is phenol made from cumene?
Cumene, isopropylbenzene, is oxidised by air to cumene hydroperoxide, which is then treated with dilute acid. It splits into phenol and propanone, so the process gives two useful products at once. Most phenol produced worldwide comes this way. Other routes include fusing sodium benzenesulphonate with NaOH and warming a diazonium salt with water.
Physical properties
Read this section in the notes →Why do alcohols boil much higher than hydrocarbons and ethers of similar mass?
The –OH group lets alcohol molecules form hydrogen bonds with one another, and extra energy is needed to break these before the liquid can boil. Ethers and hydrocarbons have no hydrogen on oxygen, so they cannot hydrogen bond with themselves. Ethanol boils at 351 K, far above methoxymethane at 248 K, although both have the same molar mass.
Why is o-nitrophenol steam-volatile while p-nitrophenol is not?
In o-nitrophenol the –OH and –NO₂ groups are neighbours and form a hydrogen bond within the same molecule. The molecules then barely associate with each other or with water, so the compound is volatile and passes over with steam. In p-nitrophenol the groups are too far apart, so hydrogen bonds form between molecules, raising the boiling point. This difference is used to separate them.
Acidity of alcohols and phenols
Read this section in the notes →Why are alcohols weaker acids than water?
The alkyl group pushes electron density towards oxygen, making the O–H bond less polar, and it also destabilises the alkoxide ion by putting more negative charge on an oxygen already carrying a negative charge. Water has no such group. So alkoxide ions are stronger bases than hydroxide, and alcohols such as ethanol, with pKa about 15.9, are slightly weaker acids than water.
Why is phenol more acidic than ethanol?
When phenol loses H⁺, the negative charge on the phenoxide ion is spread into the benzene ring by resonance, which stabilises it. The ethoxide ion has no way to delocalise its charge, so it holds on to H⁺ much more firmly. That is why phenol, with pKa about 10, reacts with NaOH, while ethanol, with pKa about 15.9, does not.
Why is p-nitrophenol more acidic than m-nitrophenol and phenol?
A nitro group at the ortho or para position can pull the negative charge of the phenoxide ion onto itself by resonance, as well as by its −I effect, which stabilises the anion strongly. At the meta position only the weaker inductive effect works. So acidity runs p-nitrophenol (pKa 7.1) > o-nitrophenol (7.2) > m-nitrophenol (8.3) > phenol (10.0).
Esterification, HX and dehydration
Read this section in the notes →How does the Lucas test distinguish primary, secondary and tertiary alcohols?
Lucas reagent is concentrated HCl with anhydrous ZnCl₂. It converts alcohols to alkyl chlorides, which are insoluble and make the mixture turbid. Tertiary alcohols react through a stable carbocation and turn turbid at once at room temperature. Secondary alcohols take a few minutes, and primary alcohols stay clear at room temperature and react only on heating.
Why do tertiary alcohols dehydrate much more easily than primary alcohols?
Acid-catalysed dehydration passes through a carbocation, and a tertiary carbocation is the most stable, so it forms easily. Tertiary alcohols lose water with 20% H₃PO₄ at about 358 K. Secondary alcohols need 85% acid at about 440 K, while ethanol needs concentrated sulphuric acid at about 443 K. Ease of dehydration follows 3° > 2° > 1°.
Oxidation of alcohols
Read this section in the notes →Why is PCC used to stop primary alcohol oxidation at the aldehyde?
Strong oxidants such as acidified dichromate or permanganate keep going and convert the aldehyde on to a carboxylic acid. Pyridinium chlorochromate, PCC, is a milder reagent that oxidises a primary alcohol to the aldehyde and goes no further. Secondary alcohols give ketones, and tertiary alcohols resist ordinary oxidation because they have no hydrogen on the carbinol carbon.
What does heated copper do to primary, secondary and tertiary alcohols?
Vapour of a primary or secondary alcohol passed over copper at 573 K loses hydrogen, giving an aldehyde or a ketone respectively. A tertiary alcohol has no hydrogen on its carbinol carbon to lose, so instead it loses water and forms an alkene. Isobutylene from 2-methylpropan-2-ol is the usual example of this distinction.
Reactions of phenols
Read this section in the notes →Why does phenol give 2,4,6-tribromophenol with bromine water but monobromophenols in CS₂?
The –OH group strongly activates the ring towards electrophiles, especially at the ortho and para positions. In water, phenol partly ionises to the even more reactive phenoxide ion and bromine is polarised, so all three positions are substituted at once and a white precipitate forms. In a low-polarity solvent such as CS₂ at low temperature, the reaction is gentler and gives o- and p-bromophenol.
What is the difference between the Kolbe reaction and the Reimer-Tiemann reaction?
Both introduce a group ortho to the –OH of phenol, but the groups differ. In the Kolbe reaction, sodium phenoxide is heated with carbon dioxide and then acidified, giving salicylic acid, with –COOH. In the Reimer-Tiemann reaction, phenol is treated with chloroform and NaOH, giving salicylaldehyde, with –CHO, through a dichlorocarbene intermediate.
What does phenol give on heating with zinc dust?
Zinc dust removes the oxygen and converts phenol into benzene. This reaction is useful in conversion questions because it lets you remove an –OH group from a ring. Phenol oxidised with chromic acid gives benzoquinone, a conjugated diketone, which is another product frequently asked about.
Methanol and ethanol
Read this section in the notes →Why is methanol so dangerous to drink?
Liver enzymes convert methanol to methanal and then to methanoic acid, which are far more toxic than methanol itself. Even a little can damage the optic nerve and leave a person blind, and a larger dose can kill. Treatment involves giving ethanol, which is oxidised by the same enzyme in preference, slowing the conversion of methanol so the kidneys can remove it unchanged.
Preparing ethers
Read this section in the notes →Why does the Williamson synthesis need a primary alkyl halide?
The alkoxide ion is a strong base as well as a nucleophile. With a primary halide, it attacks the carbon by SN2 and an ether forms. With secondary and especially tertiary halides, the alkoxide removes a hydrogen instead, so elimination gives an alkene. So to make tert-butyl methyl ether, use sodium tert-butoxide with methyl bromide, not sodium methoxide with tert-butyl bromide.
Ethers: properties and reactions
Read this section in the notes →Why does anisole with HI give phenol and methyl iodide, not iodobenzene and methanol?
The O–aryl bond is strengthened by partial double-bond character, because oxygen's lone pair is shared with the ring, so iodide cannot break it. The O–CH₃ bond is weaker, and iodide attacks the methyl carbon by SN2. So the products are phenol and CH₃I. If one alkyl group is tertiary, cleavage goes by SN1 instead, and the halide forms on that tertiary carbon.
Why is the methoxy group in anisole ortho and para directing?
The oxygen of –OCH₃ shares its lone pair with the benzene ring by resonance, increasing electron density at the ortho and para positions. Electrophiles therefore attack those positions, and anisole undergoes halogenation, nitration and Friedel-Crafts reactions more readily than benzene. For instance, bromination in ethanoic acid gives mainly p-bromoanisole even without a catalyst.
Lumi is not affiliated with or endorsed by NCERT. The official NCERT textbooks are free to read and download from NCERT's own website, ncert.nic.in. These notes and simulations are original work by Lumi (Aikolumi Software Pvt Ltd), © 2026, shared under CC BY-NC 4.0: copy, print, share and adapt them for any non-commercial use, with credit to Lumi and a link to lumineet.com.