HardChemistryHigh School (11–12)Organic Compounds with Functional Groups › Alcohols, Phenols and EthersNumerical
3,3-Dimethylbutan-2-ol, (CH₃)₃CCH(OH)CH₃, is heated with concentrated hydrobromic acid…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
3,3-Dimethylbutan-2-ol, , is heated with concentrated hydrobromic acid. The alcohol loses water to give a secondary carbocation. A methyl group then moves to the positive carbon, and bromide joins the new cation. Count the alkyl groups bonded to the positive carbon before and after the shift. Use for the alcohol and for the main product, 2-bromo-2,3-dimethylbutane. Find the mass of the main product from of alcohol at an yield.
Need a reminder? The key ideaShow
Work from the target backwards. A Grignard reagent adds its R group to a carbonyl carbon. A carbocation can shift a hydrogen or a methyl group to a more stable cation. The overall yield of a route is the product of its step yields, and a count of the starting material divides by that yield.
The worked solution
Have you tried it?
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. of alcohol, yield.
Step 1. Before. The positive carbon in is bonded to a methyl group and to the tert-butyl group: 2 alkyl groups. It is a secondary cation.
Step 2. After. A methyl group moves from the tert-butyl carbon to the positive carbon. The new positive carbon, in , is bonded to two methyl groups and to an isopropyl group: 3 alkyl groups. It is a tertiary cation, which is more stable.
Step 3. The mass. . At : .
Check. The shift makes the cation more stable, which is why 2-bromo-2,3-dimethylbutane, not 2-bromo-3,3-dimethylbutane, is the main product.
Answer: 2, 3 and .
Discussion (0)
Log in to join the discussion.
Loading…