MediumChemistryHigh School (11–12)Organic Compounds with Functional Groups › Alcohols, Phenols and EthersNumerical
Draw every carbon skeleton of five carbons: pentane, 2-methylbutane and 2,2-dimethylpropane…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Draw every carbon skeleton of five carbons: pentane, 2-methylbutane and 2,2-dimethylpropane. Place the OH group on every different carbon of each skeleton, and count the molecules once only. Find the total number of alcohols of formula . Then sort them into primary, secondary and tertiary.
Need a reminder? The key ideaShow
An alcohol has OH on a saturated carbon. Class: count the carbon neighbours of the OH carbon (1 primary, 2 secondary, 3 tertiary). Name: longest chain with the OH carbon, lowest number to OH, ending -ol. Mass percentage of an element: .
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. Five carbons, one OH group, no ring and no double bond.
Plan. Take each skeleton, list its different carbons, and classify each alcohol.
Step 1. Pentane . Carbons 1 and 5 are equivalent, so are 2 and 4, and 3 stands alone. That gives 3 alcohols: pentan-1-ol (primary), pentan-2-ol (secondary), pentan-3-ol (secondary).
Step 2. 2-Methylbutane. The two methyl groups on carbon 2 are equivalent. The different carbons are the methyls, carbon 2, carbon 3 and carbon 4. That gives 4 alcohols: 2-methylbutan-1-ol (primary), 2-methylbutan-2-ol (tertiary), 3-methylbutan-2-ol (secondary), 3-methylbutan-1-ol (primary).
Step 3. 2,2-Dimethylpropane. All four methyl groups are equivalent. That gives 1 alcohol: 2,2-dimethylpropan-1-ol (primary).
Step 4. Count. alcohols. Primary: pentan-1-ol, 2-methylbutan-1-ol, 3-methylbutan-1-ol and 2,2-dimethylpropan-1-ol, so 4. Secondary: pentan-2-ol, pentan-3-ol and 3-methylbutan-2-ol, so 3. Tertiary: 2-methylbutan-2-ol, so 1.
Check. . This agrees with the lesson: eight alcohols for five carbons.
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