Question

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

Short answer

The structures of two unsaturated hydrocarbons are ethene (H2C=CH2) and ethyne (HC≡CH). Ethene is an alkene and contains a carbon-carbon double bond, while ethyne is an alkyne and has a carbon-carbon triple bond. The presence of these carbon-carbon double or triple bonds is the structural feature that makes a hydrocarbon unsaturated.

Step-by-step solution

Example 1: Ethene (An alkene)

Ethene, also known as ethylene, is the simplest unsaturated hydrocarbon and belongs to the alkene family. Alkenes have a carbon-carbon double bond in their structure. The chemical formula for ethene is C2H4. To draw the structure of ethene, we will follow these steps: 1. Draw 2 carbon atoms with a double bond between them. 2. Attach two hydrogen atoms to each carbon atom. The resulting structure will look like this: H2C=CH2

Example 2: Ethyne (An alkyne)

Ethyne, also known as acetylene, is the simplest alkyne. Alkynes are another type of unsaturated hydrocarbon, and they contain at least one carbon-carbon triple bond in their structure. The chemical formula for ethyne is C2H2. To draw the structure of ethyne, we will follow these steps: 1. Draw 2 carbon atoms with a triple bond between them. 2. Attach one hydrogen atom to each carbon atom. The resulting structure will look like this: HC≡CH

Structural feature that makes a hydrocarbon unsaturated

The presence of carbon-carbon double or triple bonds in the structure of a hydrocarbon makes it unsaturated. Alkenes and alkynes fall into the category of unsaturated hydrocarbons due to the presence of these multiple bonds, which result in fewer hydrogen atoms being bound to the carbon chain compared to their corresponding saturated hydrocarbons, alkanes.