MediumChemistryHigh School (9–10)GeneralCarbon and Its Compounds › Hydrocarbons and NomenclatureConceptualBoard Exam
Pentane, C₅H₁₂, has three isomers. A class draws five carbon skeletons for it: Five carbons in a…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Pentane, , has three isomers. A class draws five carbon skeletons for it:
- Five carbons in a straight row.
- Four in a row, with one carbon joined to the second.
- Four in a row, with one carbon joined to the third.
- Three in a row, with two carbons joined to the middle one.
- Five carbons in a row, bent into an L shape.
Which drawings show the same compound? Name the three isomers.
Need a reminder? The key ideaShow
Alkanes are saturated, , names ending in -ane. Each member of a homologous series has one more , , than the one before. Boiling points rise along the series. Isomers have the same formula and different structures.
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. Drawings 1 and 5. Bending a chain changes nothing. Both are pentane.
Step 2. Drawings 2 and 3. Numbered from the other end, a branch on the third carbon of four sits on the second. Both are 2-methylbutane.
Step 3. Drawing 4. This is 2,2-dimethylpropane.
Answer: 1 and 5 are the same, and 2 and 3 are the same. The isomers are pentane, 2-methylbutane and 2,2-dimethylpropane.
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