Identifying the Structure of Compound X

Given the reaction involves compound X with the molecular formula C₂H₄O, which reacts with HCN to form a product. The product upon hydrolysis gives lactic acid (2-hydroxypropanoic acid). Let's analyze step by step.

Step 1: Understand the Reactions Involved

Compound X (C₂H₄O) reacts with HCN. This suggests X is a carbonyl compound (aldehyde or ketone) because HCN adds to carbonyl groups via nucleophilic addition.

The reaction with HCN forms a cyanohydrin. For an aldehyde R-CHO, the product is R-CH(OH)CN.

Step 2: Hydrolysis of Cyanohydrin

The cyanohydrin upon hydrolysis gives a hydroxy acid. Specifically, hydrolysis converts -CN group to -COOH.

So, if the cyanohydrin is R-CH(OH)CN, hydrolysis gives R-CH(OH)COOH, which is a 2-hydroxy acid.

Step 3: Relate to Lactic Acid

Lactic acid is CH₃-CH(OH)-COOH (2-hydroxypropanoic acid). This means R in R-CH(OH)COOH is CH₃-.

Therefore, the cyanohydrin must be CH₃-CH(OH)CN, which comes from the carbonyl compound CH₃-CHO (acetaldehyde).

Step 4: Verify Molecular Formula

Acetaldehyde (CH₃CHO) has molecular formula C₂H₄O, which matches compound X.

Thus, X is acetaldehyde, which has the structure CH₃-CHO.

Final Answer

The structure of X is CH₃CHO, which is represented as:

Structure of acetaldehyde

This corresponds to the second option: HO–CH₂–CHO is incorrect (it is glycolaldehyde), and the others do not match.

Related Topics

Nucleophilic Addition Reactions (e.g., addition of HCN to carbonyls)
Cyanohydrin Formation and Hydrolysis
Structure and Properties of Aldehydes
Hydroxy Acids (e.g., lactic acid)

Key Formulae and Theory

Reaction with HCN: Aldehydes and ketones undergo nucleophilic addition with HCN to form cyanohydrins.

General reaction: $R - CHO + HCN \to R - CH (OH) CN$

Hydrolysis of Cyanohydrin: Cyanohydrins hydrolyze to α-hydroxy acids.

General reaction: $R - CH (OH) CN + 2 H 2 O \to R - CH (OH) COOH + NH 3$

Note: Only aldehydes and unhindered ketones form cyanohydrins readily. Acetaldehyde (an aldehyde) reacts efficiently.