© All Rights reserved @ LearnWithDash
Step-by-Step Solution
Step 1: Analyze the Ozonolysis Products
We are told that the unknown alkene “A” undergoes ozonolysis (reaction with O3 followed by Zn/H2O) to produce propanone ($CH_{3}COCH_{3}$) and ethanal ($CH_{3}CHO$) in equimolar amounts. Ozonolysis cleaves the carbon–carbon double bond, forming two carbonyl compounds. One fragment that forms the ketone (propanone) must come from a carbon in the double bond attached to two other carbon groups (making it a more substituted carbon). The other fragment forming the aldehyde (ethanal) must come from the less substituted carbon of the double bond.
Step 2: Deduce the Structure of Alkene “A”
The total number of carbons from both carbonyl products is 3 (in propanone) plus 2 (in ethanal) = 5 carbons. This suggests that the original alkene has 5 carbons. To form propanone, the double-bonded carbon must be tertiary (no hydrogen attached), and to form ethanal, the adjacent double-bonded carbon must have one hydrogen. The simplest alkene fitting this description is 2-methyl-2-butene with the structure:
CH3 – C(CH3) = CH – CH3
Step 3: Addition of HCl to Alkene “A”
Next, hydrochloric acid (HCl) adds to an alkene according to Markovnikov’s rule. This rule states that the hydrogen (H+) adds to the carbon of the double bond that already has more hydrogens, while the chloride ion (Cl–) attaches to the carbon that can best stabilize the positive charge (the more substituted carbon). In 2-methyl-2-butene:
The proton (H+) preferentially attaches to the third carbon (the one bearing a hydrogen), generating the more stable tertiary carbocation on the second carbon.
The chloride ion then attacks this tertiary carbocation, giving the major product “B.”
Step 4: Identify the Major Product “B”
The final product is 2-chloro-2-methylbutane, which has the structure shown below (Option 1 in the question):
Final Answer
The structure of product “B” formed by the addition of HCl to alkene “A” is 2-chloro-2-methylbutane, corresponding to Option 1.
Reference Solution Provided
