Hydrocarbons

To determine the most efficient way to synthesize n-propylbenzene from the given options, we need to consider the methods shownAnalysis of the Options:Option I: Step 1: Friedel-Crafts acylation of benzene with in the presence of anhydrous to give .Step 2: Wolff-Kishner reduction (using hydrazine and KOH , heat) to reduce the carbonyl group to a methylene group, forming n-propylbenzene ( ).Option II: Direct Friedel-Crafts alkylation of benzene with n-propyl chloride ( ) in the presence of anhydrous . However, this reaction often leads to rearrangement of the propyl group, forming isopropylbenzene instead of n-propylbenzene due to the formation of a more stable secondary carbocation intermediate.Option III: This method involves the formation of phenol followed by treatment with propanol ( ) in acidic conditions. This will likely lead to ether formation rather than forming n-propylbenzene.Option IV: Similar to Option III, this involves phenol followed by treatment with propene ( ) in acidic conditions. This will likely lead to ether formation or other side reactions rather than forming n-propylbenzene.Conclusion: Among the given options, Option I is the most efficient way to synthesize npropylbenzene as it involves the Friedel-Crafts acylation followed by reduction, which ensures the formation of the desired n-propyl group without rearrangement issues.Thus, the correct answer is Option I.

✅ Correct option:A

Solution:We are told:Compound Iundergoeshydroboration–oxidation→ givescompound II (an alcohol)Compound II, on oxidation withCrO₃, gives2,3-dimethylcyclohexanoneKey Reactions & ConceptsHydroboration–oxidationAddsH and OH synAnti-Markovnikov additionNo rearrangementCrO₃ oxidationSecondary alcohol →ketonePosition of –OH in compound II becomes theC=OpositionBackward AnalysisSince the final product is2,3-dimethylcyclohexanone:The ketone carbon must originally be asecondary alcoholThat alcohol came from hydroboration of analkeneTherefore,compound I must be a dimethyl-substituted cyclohexene, where:OH forms at theless substituted alkene carbonAfter oxidation, this carbon becomes the ketoneChecking the OptionsOption A:Alkene positioned such that hydroboration gives2,3-dimethylcyclohexanolOxidation gives2,3-dimethylcyclohexanone✔️Options B, C, D:Either wrong alkene position or wrong regiochemistryDo not give the required ketone after oxidation ❌✅ AnswerCorrect structure of compound I is Option A.✔️Answer: A