SolutionsCarbon Nucleophiles

All four have the cyclohex-2-en-1-yl group bonded to the carbon bearing the OH or to a neighboring one. The common reagent is cyclohex-2-en-1-ylmagnesium bromide, prepared from 3-bromocyclohexene and magnesium in ether. Each addition is followed by hydrolysis with dilute acid.

1. With acetaldehyde: 1-(cyclohex-2-en-1-yl)ethanol (secondary alcohol).
2. With formaldehyde: (cyclohex-2-en-1-yl)methanol (primary alcohol).
3. With cyclohexanone: 1-(cyclohex-2-en-1-yl)cyclohexanol (tertiary alcohol).
4. With ethylene oxide (oxirane): 2-(cyclohex-2-en-1-yl)ethanol, a primary alcohol with two more carbons.

Yes. The tertiary alcohol has three different groups on the carbinol carbon (methyl, ethyl and phenyl), and any of them can come from the Grignard reagent:

1. Phenylmagnesium bromide and butanone.
2. Ethylmagnesium bromide and acetophenone.
3. Methylmagnesium bromide and propiophenone (1-phenyl-1-propanone).

The three ketones are planar at the carbonyl and the reagent attacks both faces equally: the racemate is always obtained.

By the Wittig reaction: the C=C forms where the C=O of the aldehyde or ketone was.

1. Cyclohexanone and the phosphorus ylide derived from cyclohexyltriphenylphosphonium bromide (Ph₃P=C₆H₁₀). The reaction is slow because of steric hindrance.
2. Intramolecular Wittig: (6-oxohexyl)triphenylphosphonium bromide, treated with base, forms the ylide, which attacks the aldehyde of the same chain and closes the six-membered ring.
3. 3-Acetylcyclopentanone and two equivalents of methylenetriphenylphosphorane (Ph₃P=CH₂): both C=O groups become C=CH₂.
4. 3-Isopropylcyclopentanone and methylenetriphenylphosphorane (Ph₃P=CH₂).

The Wittig reaction places the double bond unambiguously, unlike the dehydration of alcohols, which usually gives mixtures.