A tertiary alcohol, 3-methylpentan-3-ol, (C₂H₅)₂C(CH₃)OH, is to be made with a Grignard reagent…
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A tertiary alcohol, 3-methylpentan-3-ol, , is to be made with a Grignard reagent. Find the number of different ketone and Grignard pairs that give it. Then find the mass of magnesium, in g, needed to make of the Grignard reagent from a haloalkane. Use for magnesium.
Need a reminder? The key ideaShow
Acid hydration puts OH on the more substituted carbon. Hydroboration then oxidation puts it on the less substituted carbon, and one BH takes three alkene molecules. NaBH reduces four C=O groups for each formula unit. A Grignard reagent adds its R group to the carbonyl carbon. Yield .
The worked solution
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Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Given. The OH carbon holds a methyl group and two ethyl groups.
Step 1. The pairs. Choose which one of the three groups comes from the Grignard reagent. The two ethyl groups are the same. Pair one: methylmagnesium bromide with pentan-3-one, . Pair two: ethylmagnesium bromide with butan-2-one, . That is 2 pairs.
Step 2. Magnesium. The reaction is , one magnesium for each reagent. .
Check. An ester of ethanoic acid and two molecules of ethylmagnesium bromide also give this alcohol. The question asked for ketone pairs only, so the answer stays 2.
Answer: 2 pairs and of magnesium.
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