40 8.1 Introduction to Hydrocarbons

Practice questions

1. Which of the following are alkanes?
   1. 1. Cyclohexane ring: six carbons in a hexagon, [latex]\ce{C}[/latex]s are located at each point of the hexagon and connected by [latex]\ce{C}[/latex]–[latex]\ce{C}[/latex] single bonds.
      2. Benzene ring: six carbons in a hexagon, [latex]\ce{C}[/latex]s are located at each point of the hexagon. Alternative [latex]\ce{C}[/latex]s form double bonds with the following [latex]\ce{C}[/latex].
      3. Two carbons are arranged in a continuous chain with one triple bond between two carbons.
      4. Four carbons are arranged in a Y-shaped structure. Three [latex]\ce{CH_{3}}[/latex] groups are located at the outer points of the Y-shape structure, while one [latex]\ce{CH_{2}}[/latex] group situated at the junction of the Y-shape structure.
      5. Eight carbons form a branching structure. The third and fifth carbons have methyl groups attached to those carbons.
2. Select all the alkene structures shown here:
   1. 1. Five carbons are located in a plus-shaped structure. Four outer carbons are methyl groups, while a carbon located at the middle point of the plus-shaped structure forms single bonds with four outer methyl groups.
      2. Two carbon structures with a double bond between two carbons.
      3. Five carbon structures with two [latex]\ce{C}[/latex]–[latex]\ce{C}[/latex] bonds: one double bond between second and third carbon and the other between fourth and fifth carbon.
      4. Six carbon structures with a single, double bond in a branched chain. The second and third carbons have methyl groups attached to each carbon. [latex]\ce{C}[/latex]–[latex]\ce{C}[/latex] bond located between second and third carbon.
      5. Benzene ring: six carbons in a hexagon, [latex]\ce{C}[/latex]s are located at each point of the hexagon. Alternative [latex]\ce{C}[/latex]s form double bonds with the following [latex]\ce{C}[/latex].
3. Which of the following belongs to the alkyne family?
   1. 1. Two carbons are arranged in a continuous chain with one triple bond between two carbons.
      2. A structure with one carbon, one hydrogen and one nitrogen. A triple bond is located between [latex]\ce{C}[/latex] and [latex]\ce{N}[/latex]. One hydrogen is attached to the carbon.
      3. Eight carbons form a branched structure. Six carbons out of eight are arranged in a continuous chain with a [latex]\ce{C}[/latex]–[latex]\ce{C}[/latex] bond located between the third and fourth carbons. The second and fifth carbons have methyl groups attached to each carbon.
      4. Six carbons arranged in a continuous chain with two [latex]\ce{C}[/latex]–[latex]\ce{C}[/latex] triple bonds located in the second and third carbons and the fourth and fifth carbons.
      5. Six carbon structures with one double bond in a branched chain. The second and third carbons have methyl groups attached to each carbon. A [latex]\ce{C}[/latex]–[latex]\ce{C}[/latex] bond is located between the second and third carbon.
4. Alkanes are less reactive compared to other hydrocarbons. Which of the following is the correct explanation for alkanes’ reactivity?
   1. 1. Alkanes are less reactive because of strong  [latex]\ce{C}[/latex]–[latex]\ce{C}[/latex] and [latex]\ce{C}[/latex]–[latex]\ce{H}[/latex] single bonds.
      2. Alkanes are less reactive because of the non-polar nature of C−C and C−H bonds.
      3. Alkanes are less reactive because they are polar molecules.
      4. a and b
5. Which of the following belongs to the hydrocarbon family?
   1. 1. A structure with two carbons. A carboxylic group ([latex]\ce{COOH}[/latex]) and a [latex]\ce{NH_{2}}[/latex] attached to the first carbon.
      2. Three benzene rings fused together.
      3. One benzene ring with a [latex]\ce{CH_{2}-O-CH=O}[/latex] attached to the first carbon of the benzene ring.
      4. Five carbons located in a plus-shaped structure. Four outer carbons are methyl groups, while a carbon located at the middle point of the plus-shape structure forms single bonds with four outer methyl groups.
      5. A four-carbon continuous chain. A [latex]\ce{C}[/latex]–[latex]\ce{C}[/latex] triple bond is located between the second and the third carbons.
6. Explain the difference between saturated and unsaturated hydrocarbons by filling the blanks.

The difference between saturated and unsaturated hydrocarbons lies in the nature of the ………………. bonds: saturated hydrocarbons have only ……………., while unsaturated hydrocarbons have at least one ………….. or …………….. bond. The carbon atoms in saturated hydrocarbons are saturated with …………….. atoms, meaning they are bonded to as many …………… atoms as ……….. . Unsaturated hydrocarbons have at least one carbon-carbon …………. or …………….. bond, resulting in fewer …………………… atoms bonded to the …………….. atoms. This distinction affects the overall ……………….., ………………………., and ………………… properties of these hydrocarbons.

Answers

1. a, d,  e
2. b, c, d, e
3. a, c, d
4. d
5. b, d, e
6. carbon-carbon, single, double, triple, hydrogen, hydrogen, possible, double, triple, hydrogen, carbon, structure, reactivity, physical