Question

Draw the structures for two examples of unsaturated hydrocarbons. What structural feature makes a hydrocarbon unsaturated?

Short answer

Two examples of unsaturated hydrocarbons are ethene (C2H4) and ethyne (C2H2). Ethene has a double bond between the carbon atoms and its structure is: H | H─C= C─H | H Ethyne has a triple bond between the carbon atoms and its structure is: H | H─ C≡C─H The structural feature that makes a hydrocarbon unsaturated is the presence of at least one double or triple bond between the carbon atoms in the molecule. In the cases of ethene and ethyne, this feature can be seen as the double bond (=) and triple bond (≡) between the carbon atoms, respectively.

Step-by-step solution

Draw an alkene structure (double bond)

To draw an alkene structure, we will first choose a simple example: ethene (C2H4). It has two carbon atoms double-bonded to each other, and each carbon atom has two hydrogen atoms bonded to them. The structure for ethene is as follows: H | H─C= C─H | H

Draw an alkyne structure (triple bond)

To draw an alkyne structure, we will select a simple example: ethyne (C2H2). It has two carbon atoms triple-bonded to each other, and each carbon atom has one hydrogen atom bonded to them. The structure for ethyne is as follows: H | H─ C≡C─H

Identify the structural feature that makes a hydrocarbon unsaturated

The structural feature that makes a hydrocarbon unsaturated is the presence of at least one double or triple bond between the carbon atoms in the molecule. In the cases of ethene and ethyne, this feature can be seen as the double bond (=) and triple bond (≡) between the carbon atoms, respectively. These double and triple bonds reduce the number of hydrogen atoms that can be bonded to the carbon atoms, making the hydrocarbon less saturated with hydrogen than an equivalent alkane with only single bonds.