HardChemistryHigh School (11–12)Organic Chemistry: Some Basic Principles and Techniques › Classification, IUPAC Nomenclature and IsomerismNumericalpython
A hydrocarbon has the formula C₄H₈. Find its degrees of unsaturation…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A hydrocarbon has the formula . Find its degrees of unsaturation. Then find how many structural isomers it has, counting rings as well as double bonds. How many isomers are there when the cis and trans forms are counted separately?
Need a reminder? The key ideaShow
Isomers have the same molecular formula and different structures. Structural: chain, position, functional group, metamerism, tautomerism. Stereo: geometrical (each end of a double bond has two different groups) and optical (a carbon with four different groups). Degrees of unsaturation: . Up to stereoisomers for n different stereocentres.
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.
Step 1. Unsaturation. . So there is one double bond or one ring.
Step 2. Double bond. Chain: but-1-ene and but-2-ene. Branched: 2-methylpropene. That is 3.
Step 3. Ring. Cyclobutane and methylcyclopropane. That is 2, so 5 structural isomers.
Step 4. Cis and trans. But-2-ene has two different groups on each end of its double bond, so it has a cis and a trans form. The others have none. The total is 6.
Answer: 1, then 5, then 6.
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