2.7: Carbon Skeletons
All organic compounds have a carbon skeleton as their backbone. Each carbon atom can form four bonds. As the carbon skeleton increases in length, structural modifications such as ring structures, double bonds, and branching side chains become possible.
Carbon Is the Basis of Organic Molecules
Life on Earth is carbon-based as all macromolecules that make up living organisms contain carbon atoms. Carbon can form four bonds and rarely becomes an ion, making it an extraordinarily flexible component of biological molecules.
Carbon-carbon bonds form the basis of the carbon skeleton. Hydrogen atoms readily bond to the carbon atom. Molecules that contain only hydrogen and carbon are called hydrocarbons. Hydrocarbons usually form either long chains or will have branches protruding at various points. Changing the number of bonds changes the properties of the molecule. For example, a fatty acid with a long hydrocarbon tail with one or more double bonds will behave differently than a fatty acid with no double bonds.
Isomers Are Different Ways to Arrange the Same Number of Atoms
Molecules with the same chemical formula but with different structures are called isomers. One example of isomers can be seen in two different molecules that share the chemical formula C6H14. Hexane has a single chain of carbon atoms, while isohexane has a branch point on the second carbon atom. Some isomers are mirror images of each other, which are called enantiomers.
Functional Groups Build on Carbon Skeletons
The unique properties of biological molecules are conferred by functional groups bonded to the carbon skeleton, such as amino (–NH2) or methyl groups (–CH3). Functional groups can alter the structural and chemical properties of the molecule. Knowledge of the properties of functional groups influences many fields of study, such as synthetic drug design.