To solve the problem, we need to determine the relationship between compounds A and C in the given reaction sequence starting from CHβCHO (acetaldehyde) and leading to the final product C.
1. Understanding the First Step (CHβCHO to A):
The starting compound is CHβCHO (acetaldehyde), and the reagents are (i) CHβMgBr and (ii) HβOβΊ. CHβMgBr is a Grignard reagent, which reacts with the carbonyl group of aldehydes to form alcohols. For acetaldehyde (CHβCHO), the carbonyl carbon is attacked by the nucleophilic CHββ» from CHβMgBr, forming a tetrahedral intermediate. After hydrolysis with HβOβΊ, this yields a secondary alcohol:
CHβCHO + CHβMgBr β (CHβ)βCHOMgBr β (CHβ)βCHOH (2-propanol, a secondary alcohol).
Thus, A is (CHβ)βCHOH.
2. Analyzing the Second Step (A to B):
Compound A undergoes a reaction with conc. HβSOβ and heat (Ξ). Concentrated HβSOβ at high temperature typically dehydrates alcohols to form alkenes via an elimination reaction (E1 or E2 mechanism). For (CHβ)βCHOH (2-propanol), dehydration removes a water molecule, forming propene:
(CHβ)βCHOH β CHβCH=CHβ + HβO.
Thus, B is CHβCH=CHβ (propene).
3. Analyzing the Third Step (B to C):
Compound B reacts with (i) BβHβ and (ii) HβOβ, OHβ». This is a hydroboration-oxidation reaction, which converts alkenes to alcohols with anti-Markovnikov addition and syn orientation. For propene (CHβCH=CHβ), the double bond is between the first and second carbons. In hydroboration, the boron from BβHβ adds to the less substituted carbon (the terminal carbon, CHβ), and the hydrogen adds to the more substituted carbon (CHCHβ). Subsequent oxidation with HβOβ and OHβ» replaces the boron with an OH group, yielding a primary alcohol:
CHβCH=CHβ β CHβCHβCHβOH (1-propanol, a primary alcohol).
Thus, C is CHβCHβCHβOH.
4. Comparing Compounds A and C:
- A is (CHβ)βCHOH (2-propanol), a secondary alcohol with the structure CHβ-CH(OH)-CHβ.
- C is CHβCHβCHβOH (1-propanol), a primary alcohol with the structure CHβ-CHβ-CHβ-OH.
Both A and C have the same molecular formula (CβHβO) since they are both alcohols with three carbons. However, the position of the OH group differs: in A, the OH is on the second carbon, and in C, the OH is on the first carbon.
5. Determining the Type of Isomerism:
- Since A and C have the same molecular formula (CβHβO) but differ in the position of the functional group (OH), they are positional isomers.
- They are not identical (different structures).
- They are not functional isomers (both are alcohols).
- They are not optical isomers (neither has a chiral center; A has a plane of symmetry, and C is a primary alcohol with no chiral carbon).
Final Answer:
A and C are positional isomers, so the answer is (B).