44 8.5 Isomers

Practice questions

1. Which structures among those shown here are related to one another as constitutional isomers? Select all that belong in the set.
   1. 1. A five-carbon ring with two carbon double bonds located in alternative carbons.
      2. A four-carbon straight chain with a $\mathrm{NH}$ group located between the second and third carbon and a methyl group attached to the second and third carbons, each.
      3. A five-carbon straight chain with two carbon double bonds: one double bond between the first and the second carbon and the other third and the fourth carbon.
      4. A six-carbon straight chain with a $\mathrm{NH}{\phantom{A}}_2$ attached to the last carbon.
2. What is the constitutional isomer of ethanol, $\mathrm{CH}{\phantom{A}}_3\mathrm{CH}{\phantom{A}}_2\mathrm{OH}$?
   1. 1. A two-carbon chain with a hydroxyl group attached to $\mathrm{CH}{\phantom{A}}_2$:  $\mathrm{CH}{\phantom{A}}_3\mathrm{CH}{\phantom{A}}_2\mathrm{OH}$
      2. A two-carbon chain with a hydroxyl group attached to $\mathrm{CH}{\phantom{A}}_2$: $\mathrm{CH}{\phantom{A}}_3\mathrm{CH}{\phantom{A}}_2\mathrm{OH}$
      3. A two-carbon chain with an oxygen atom connecting two carbons: $\mathrm{CH}{\phantom{A}}_3\mathrm{OCH}{\phantom{A}}_3$
3. Is it true that this is a constitutional isomer of resorcinol, molecular formula $\mathrm{C}{\phantom{A}}_6\mathrm{H}{\phantom{A}}_6\mathrm{O}{\phantom{A}}_2$? The structure description: a benzene ring with two hydroxyl groups attached to carbons opposite to each other.
4. How many constitutional isomers does $\mathrm{C}{\phantom{A}}_5\mathrm{H}{\phantom{A}}_{12}$ have?
   1. 1. 3
      2. None
      3. 2
      4. 4
5. How many constitutional isomers does $\mathrm{C}{\phantom{A}}_4\mathrm{H}{\phantom{A}}_{10}\mathrm{O}$ have?
   1. 1. 4
      2. 3
      3. 10
      4. 7
6. How many structural isomers does $\mathrm{C}{\phantom{A}}_3\mathrm{H}{\phantom{A}}_9\mathrm{N}$ have?
   1. 1. 3
      2. 2
      3. 4
      4. 7

Answers

1. b, d
2. c
3. True
4. a
5. 7
6. c