Read the passage carefully and answer the questions based on the passage:
Alcohols are versatile compounds as they can act as both nucleophile and electrophiles. They undergo reactions based on cleavage of O-H and C-O bonds. The cleavage of O-H bond reflects the acidic character of alcohols. However they are weaker acids than water, phenol and carboxylic acids. Alkoxide ion formed by loss of proton from the OH group of alcohols react with water to form the corresponding conjugate acid-base pair. They act as Bronsted base due to presence of unshared electron pairs on oxygen.Both alcohols and phenol react with carboxylic acids, acid chlorides and anhydrides to form esters. The introduction of acetyl group in alcohols or phenol is known as acetylation. Alcohols react with hydrogen halides to form alkyl halides which form the basis of Lucas test. They also undergo acid catalyzed dehydration to form alkenes. Alcohols can be easily oxidized with variety of oxidizing agents. The nature of the product depends on the type of oxidizing agent and the nature of alcohol.
Which of the following gives the correct sequential steps for dehydration of alcohol?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Formation of protonated alcohol, formation of carbocation, elimination of a proton
Acid-catalysed dehydration of an alcohol is an elimination through a carbocation. The –OH group is a poor leaving group, so the acid first converts it into –\( \ce{OH2^{+}} \), which can leave as a neutral water molecule. For ethanol with concentrated \( \ce{H2SO4} \) at 443 K, the steps are as follows.
The three steps are protonation of the alcohol, loss of water to give a carbocation (the slow step), and loss of a proton to give the alkene; the acid used in the first step is given back in the last.
Shortcut: The first event must be the attack of the acid on the alcohol (protonation), and the last must give the alkene (loss of a proton). Only Option (2) begins with protonation and ends with elimination of a proton.
NCERT (2026-27 edition):
Dehydration – …
