Hydrocarbons are organic compounds that consist entirely of carbon and hydrogen atoms. Hydrocarbons can form different functional groups based upon their carbon bonding patterns as alkanes, alkenes, alkynes, or arenes.
The carbon-carbon single bonds of alkanes rotate freely. Conformers are the same molecule shown with different sigma bond rotations. Newman projections are one way to communicate bond rotation.
The conformations of butane are studied to introduce the language and energetic considerations of single bond rotation when alkyl group interactions can occur.
Pentane and higher alkanes have conformational preferences similar to ethane and butane. Each dihedral angle tries to adopt a staggered conformation and each internal C-C bond attempts to take on an anti conformation to minimize the potential energy of the molecule.
For cyclic alkanes, only partial rotation of carbon-carbon single bonds can occur. The actual shape of the carbon ring distorts from the traditional geometric shapes to reduce steric hindrance and ring strain to lower the overall potential energy of the molecule.
Cyclohexane rings are notably stable. Understanding the conformations of cyclohexane and their relative energies is helpful when studying the chemistry of simple carbohydrates (monosaccharides).
Stereoisomerism is possible for cycloalkanes with two different substituent groups (not counting other ring atoms). Cis and trans isomers are unique compounds.
Because six-membered rings are so common among natural and synthetic compounds and its conformational features are rather well understood, we shall focus on the six-membered cyclohexane ring to study the energetic relationship of conformation and overall potential energy.
The primary sources for alkanes are oil and natural gas. Alkanes are important raw materials for the chemical industry and are used as fuels for motors.
Alkanes (the most basic of all organic compounds) undergo very few reactions. The two reactions of more importaces is combustion and halogenation, (i.e., substitution of a single hydrogen on the alkane for a single halogen) to form a haloalkane. The halogen reaction is very important in organic chemistry because it opens a gateway to further chemical reactions.