In the conversion of ethanol to ethene, the first step of the reaction involves the formation of
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Oxonium ion
Ethanol has a poor leaving group ($-OH$). Acid converts it into a better leaving group (water).
Step 1 (First step): Protonation
$CH_3CH_2OH+ H^+ → CH_3CH_2OH_2^+$
This protonated alcohol is called an oxonium ion.
After this:
- Water leaves
- Carbocation forms
- Then elimination gives ethene
Explanation of each option
1. Oxonium ion
Formed when ethanol's oxygen gets protonated in acidic medium. This converts $-OH$ into $-OH_2^+$,making water a good leaving group. This is always the first step in acid-catalysed dehydration of alcohols.
2. Carbonium ion
Carbocation forms only after water leaves from the oxonium ion. So this is a later intermediate, not the first one.
3. Carbene
Carbenes are neutral divalent carbon species (like: $CH_2$). They are not formed in alcohol dehydration reactions.
4. Carbanion ion
Carbanions are negatively charged carbon species, formed in strongly basic conditions. This reaction occurs in acidic medium, so impossible.