What is the difference between saturated and unsaturated hydrocarbons?

Saturated hydrocarbons are the simplest type of organic compounds, consisting solely of carbon and hydrogen atoms, where all the carbon-carbon bonds are single bonds. This structure gives them a general formula of C_nH_2n+2 for molecules without rings. Imagine them as being 'saturated' with hydrogen atoms since no more can be added without breaking the existing carbon-carbon single bonds.

Common examples include methane (CH₄), ethane (C₂H₆), and propane (C₃H₈). These molecules are also known as alkanes and are noted for being relatively non-reactive due to the stability of their carbon-to-carbon bonds. Saturated hydrocarbons are typically found in natural gas and petroleum and are used as fuels, providing energy when combusted.

In contrast to their saturated counterparts, unsaturated hydrocarbons contain one or more carbon-carbon double or triple bonds. These additional bonds mean they have fewer hydrogen atoms than the maximum possible, which is why we term them 'unsaturated'.

The presence of these multiple bonds introduces kinks and bends in the hydrocarbon chains, affecting their physical properties and reactivity. Unsaturated hydrocarbons with double bonds are called alkenes, with the simplest member being ethene (C₂H₄). Compounds with triple bonds are called alkynes, with acetylene (C₂H₂) as a basic example. They are known for being more reactive than alkanes because the multiple bonds can readily react with other substances in addition reactions, a key characteristic that distinguishes them from saturated hydrocarbons.

The characteristics of hydrocarbons depend largely on the types of bonds between the carbon atoms. Single bonds, as found in saturated hydrocarbons, allow for rotation around the bond axis, leading to a more flexible structure. Multiple bonds, characteristic of unsaturated hydrocarbons, restrict such rotation and contribute to rigidity.

Chemical Stability

Single bonds are generally stronger and less reactive than double or triple bonds. This makes saturated hydrocarbons less likely to undergo chemical reactions. On the other hand, the electron-rich regions of double and triple bonds in unsaturated hydrocarbons make them more susceptible to attacks by electrophiles, substances that seek out electrons, increasing their likelihood of participating in chemical reactions, particularly addition reactions.

Addition reactions are a hallmark of unsaturated hydrocarbons. These reactions involve adding atoms across the double or triple bonds, effectively 'saturating' the molecule. For instance, the addition of hydrogen in a process known as hydrogenation transforms an alkene into an alkane.

Commercial Relevance

The ability to undergo addition reactions makes unsaturated hydrocarbons versatile in the industrial synthesis of a wide array of products, including polymers, alcohols, and other organic compounds. This is significantly useful in the production of plastics, synthetic rubbers, and various chemicals. These reactions are not applicable to saturated hydrocarbons because their single bonds do not easily break to allow the addition of new atoms.