Question

Choose the incorrect statement.

• A. Cresols are less acidic than Phenol because electron releasing groups do not favour formation of Phenoxide ion.
• B. Ethanol acts as Nucleophile when the \( O-H \) bond is broken and acts as Electrophile on getting protonated.
• C. In the acid catalysed hydration of Ethene, an Oxonium ion is formed when it reacts with \( H_3O^+ \) and a Carbocation is formed when the Oxonium ion reacts with water.
• D. In the reaction between Ethanol and Conc. \( H_2SO_4 \) at 413 K, an Oxonium ion is formed when Ethanol gets protonated.

Hint:

In acid catalysed hydration of alkenes, the correct order is protonation of alkene to form carbocation, attack by water to form oxonium ion, and then deprotonation to form alcohol.

Answer 1

The Correct Option is C

Step 1: Understand the question.
The question asks us to identify the incorrect statement among the given options.

Step 2: Analyze statement (A).
Cresols contain a methyl group attached to the benzene ring.
The methyl group is an electron releasing group and increases electron density on the ring.
This destabilizes the phenoxide ion formed after loss of \( H^+ \).
Therefore, cresols are less acidic than phenol.
So, statement (A) is correct.

Step 3: Analyze statement (B).
Ethanol can act as a nucleophile due to the lone pair of electrons present on oxygen.
When ethanol gets protonated, it forms an oxonium ion.
The protonated ethanol becomes more reactive and can behave as an electrophilic species because water becomes a good leaving group.
So, statement (B) is correct.

Step 4: Understand acid catalysed hydration of ethene.
In acid catalysed hydration of ethene, ethene first reacts with \( H_3O^+ \).
The double bond attacks \( H^+ \), and a carbocation is formed first.
\[ CH_2=CH_2 + H^+ \rightarrow CH_3CH_2^+ \]

Step 5: Correct sequence after carbocation formation.
After formation of carbocation, water attacks the carbocation to form an oxonium ion.
\[ CH_3CH_2^+ + H_2O \rightarrow CH_3CH_2OH_2^+ \]
Finally, deprotonation gives ethanol.
\[ CH_3CH_2OH_2^+ \rightarrow CH_3CH_2OH + H^+ \]

Step 6: Analyze statement (C).
Statement (C) says that oxonium ion is formed first and carbocation is formed later when oxonium ion reacts with water.
This is the reverse of the correct mechanism.
Actually, carbocation is formed first, then water attacks it to form oxonium ion.
Hence, statement (C) is incorrect.

Step 7: Analyze statement (D).
In the reaction of ethanol with concentrated \( H_2SO_4 \) at 413 K, ethanol gets protonated first.
This forms an oxonium ion.
Therefore, statement (D) is correct.
Thus, the incorrect statement is:
\[ \boxed{\text{Statement (C)}} \]