Definitions of Alkanes and Cycloalkanes
Hydrocarbons contain only carbons and hydrogens. Alkanes are noncyclic compounds that contain carbons and hydrogens. Cycloalkanes are cyclic compounds that contain carbons and hydrogens.
Background Information for Alkanes and Cycloalkanes
Alkanes and cycloalkanes are nonpolar and do not have intermolecular hydrogen bonding. These compounds are hydrophobic, do not dissolve in water, and are less dense than water. The boiling points and melting points of alkanes and cycloalkanes increase with increasing molecular weight. The conformations of ethane are eclipsed and staggered. The conformations of butane are totally eclipsed, gauche, eclipsed, and anti. Smaller rings are more likely to undergo ring opening reactions. The main conformations of cyclohexane are chair and boat. Cyclopropane has a carbon-carbon bond angle of 60o. Cyclobutane has a carbon-carbon bond angle of 90o. Cyclopentane has a carbon-carbon bond angle of 108o. Cyclohexane has a carbon-carbon bond angle of 109.5o. The chair conformation of cyclohexane is the most stable, with the hydrogens furthest apart. The boat conformation of cyclohexane is the least stable, with the hydrogens the closest.
Uses of Alkanes and Cycloalkanes
The uses of alkanes and cycloalkanes are defined by the carbon number: C1 B C4 B natural gas, petroleum gas, C5 B C12 B motor fuel, C12 B C13 B kerosene, C15 B C25 B diesel, C16 - C30 -- heavy oil, >C25 B petroleum jelly or paraffin wax, and residue B asphalt.
IUPAC Nomenclature for Alkanes and Cycloalkanes
The longest continuous chain is the parent compound. Number from whichever end that gives the lowest possible combination of numbers for the alkyl groups. Number the cycloalkane so that the lowest possible combination of numbers are used for the substituents. If the compound contains an aliphatic ring and an aliphatic chain, the parent compound is the one with the most carbons.
Use n, iso, sec, tert, and neo prefixes.
Reactions of Alkanes
Combustion converts alkanes to carbon dioxide and water. Cracking of hydrocarbons at high temperatures yield a mixture of smaller alkanes and alkenes. Halogenation of alkanes occurs with halogen in the presence of heat or light and through a radical mechanism. In the mechanism of halogenation, radicals are formed in initiation. In propagation, radicals are consumed and radicals are formed. In termination, the radical are consumed.
Reactions of Cycloalkanes
Halogenation of cycloalkanes occurs in the presence of heat or light to form a halogenated cycloalkane. Ring opening of cyclopropane occurs with hydrogen halide to form 1-halopropane. Ring opening of cyclopropane occurs with halogen to give 1,3-dichloropropane. Ring opening of cyclopropane occurs with hydrogen to produce propane. Ring opening of cyclobutane occurs with hydrogen to produce butane.