# 2: Alkanes and Cycloalkanes

• 2.1: Structures and Names of Alkanes
Simple alkanes exist as a homologous series, in which adjacent members differ by a $$CH_2$$ unit.
• 2.2: Branched-Chain Alkanes
Alkanes with four or more carbon atoms can exist in isomeric forms.
• 2.3: Condensed Structural and Skeletal Formulas
Condensed structural formulas show the hydrogen atoms (or other atoms or groups) right next to the carbon atoms to which they are attached. Skeletal formulas imply a carbon atom at the corners and ends of lines. Each carbon atom is understood to be attached to enough hydrogen atoms to give each carbon atom four bonds.
• 2.4: IUPAC Nomenclature
Alkanes have both common names and systematic names, specified by IUPAC. IUPAC is the International Union of Pure and Applied Chemistry.
• 2.5: Halogenated Hydrocarbons
The replacement of an hydrogen atom on an alkane by a halogen atom—F, Cl, Br, or I—forms a halogenated compound.
• 2.6: Conformations of Ethane
Conformational isomerism involves rotation about sigma bonds, and does not involve any differences in the connectivity or geometry of bonding. Two or more structures that are categorized as conformational isomers, or conformers, are really just two of the exact same molecule that differ only in terms of the angle about one or more sigma bonds.
• 2.7: Conformations of Other Alkanes
Ethane has only two conformers of note - staggered and eclipsed.  Alkanes that are more complex than ethane, like propane and butane have a greater variety in possible conformers and their relative energies.
• 2.8: Source of hydrocarbons- crude oil and natural gas
The petroleum that is pumped out of the ground at locations around the world is a complex mixture of several thousand organic compounds, including straight-chain alkanes, cycloalkanes, alkenes, and aromatic hydrocarbons with four to several hundred carbon atoms. The identities and relative abundances of the components vary depending on the source.
• 2.9: Cycloalkanes
Many organic compounds have cyclic structures.
• 2.10: Naming Cycloalkanes
Cycloalkanes have one or more rings of carbon atoms, and contain only carbon-hydrogen and carbon-carbon single bonds. The naming of cycloalkanes follows a set of rules similar to that used for naming alkanes.
• 2.11: Stability of Cycloalkanes - Ring Strain
Small cycloalkanes, like cyclopropane, are dramatically less stable than larger cycloalkanes due to ring strain.  Ring strain is caused by increased torsional strain, steric strain, and angle strain, in the small, nearly planar ring of cyclopropane.  Larger rings like cyclohexane, have much lower ring straing because they adopt non-planar conformations.
• 2.12: Cis-Trans Isomerism in Cycloalkanes
Stereoisomers are molecules that have the same molecular formula, the same atom connectivity, but they differ in the relative spatial orientation of the atoms.  Di-substituted cycloalkanes are one class of molecules that exhibit stereoisomerism.  Di-substituted cycloalkane stereoisomers are designated by the nomenclature prefixes cis (Latin, meaning on this side) and trans (Latin, meaning across).
• 2.13: Conformations of Cyclohexane
Rings larger than cyclopentane would have angle strain if they were planar. However, this strain, together with the eclipsing strain inherent in a planar structure, can be relieved by puckering the ring. Cyclohexane is a good example of a carbocyclic system that virtually eliminates eclipsing and angle strain by adopting non-planar conformations.
• 2.14: Axial and Equatorial Bonds in Cyclohexane
The hydrogens of cyclohexane exist in two distinct locations - axial and equatorial.  The two chair conformations of cyclohexane rapidly interconverts through a process called ring flip.
• 2.15: Conformations of Monosubstituted Cyclohexanes
Mono-substituted cyclohexane prefers the ring flip conformer in which the substituent is equatorial.  1,3-diaxial interactions occur when the substituent is axial, instead of equatorial. The larger the substituent, the more pronounced the preference.
• 2.16: Conformations of Disubstituted Cyclohexanes
The most stable configurational isomer of a disubstituted cyclohexane will be the isomer that has the most stable conformational isomer.
• 2.17: Physical Properties of Alkanes
Alkanes are nonpolar compounds that are low boiling and insoluble in water.
• 2.18: Reactions of Alkanes
This page deals briefly with the combustion of alkanes and cycloalkanes. In fact, there is very little difference between the two.. This page describes the reactions between alkanes and cycloalkanes with the halogens fluorine, chlorine, bromine and iodine - mainly concentrating on chlorine and bromine.