Find the number of isomers (alcohols and ethers) of the formula C₅H₁₂O, the number that have a…
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Find the number of isomers (alcohols and ethers) of the formula , the number that have a stereocentre, and the number of those that are alcohols. The alcohols number 8 and the ethers 6. A stereocentre is a carbon with four different groups, and a hydrogen atom counts as a group.
Need a reminder? The key ideaShow
Degree of unsaturation . Each group of equivalent hydrogens gives one NMR signal. The OH signal disappears with . The molecular ion has . Zeisel: one AgI for each OCH group, .
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. 8 alcohols and 6 ethers.
Step 1. Total. .
Step 2. Alcohols with a stereocentre. Pentan-2-ol: carbon 2 has H, OH, CH and CH. 3-Methylbutan-2-ol: carbon 2 has H, OH, CH and isopropyl. 2-Methylbutan-1-ol: carbon 2 has H, CH, CH and CHOH. The other five have none. That is 3.
Step 3. Ethers. 2-Methoxybutane has a carbon with H, OCH, CH and CH. No other ether does. That is 1.
Step 4. Together. .
Check. The program builds all 14 and finds 4 with a stereocentre.
Answer: 14, 4 and 3.
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