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Structure and Naming of Alkanes and Cycloalkanes

A cyclohexane molecule between two decane moelcules.  Graphic by Chris Jones.

Structure and Naming of Alkanes

Alkanes are hydrocarbon that have only sp3 carbons and hydrogens. Each carbon atom in the molecule is surrounded by single covalent bonds. Each carbon in an alkane is connected to four atoms in a tetrahedral geometry. Due to this geometry and the small diffence in electronegativity between hydrogen and carbon, alkanes are non-polar molecules. The general molecular formula for alkanes is:

CnH2n+2

where n = number of carbon atoms in the alkane molecule

Below is listed the names of alkanes that have all the carbon atoms connected in a continuous chain. The continuous chain does not mean that the carbons are in a straight line. These molecules have bond angles of ~109.5o and are free to rotate about any of the single bonds.

Alkanes: CnH2n+2

Name
Molecular Formula
Chemical Structure
Space-Filled Drawing
(Click for large view)
methane
CH4
methane
methane
ethane
C2H6
ethane
ethane
propane
C3H8
propane
propane
butane
C4H10
butane
butane
pentane
C5H12
pentane
pentane
hexane
C6H14
hexane
hexane
heptane
C7H16
heptane
heptane
octane
C8H18
octane
octane
noname
C9H20
nonane
nonane
decane
C10H22
decane
decane

Structure and Naming of Alkanes

Like simple alkanes, cycloalkane are also hydrocarbon that have only sp3 carbons and hydrogens. However, these hydrocarbons form rings. Cycloalkanes have the general molecular formula of:

CnH2n

where n = number of carbon atoms in the cycloalkane molecule.

The smallest cycloalkane is cyclopropane. Cyclopropane has a large angle strain since the bond angle is 60o instead of the preferred bond angle of 109.5o. Cyclobutane has a bond angle of 90o and cyclopentant has a bond angle of 108o. All of the carbons lie in the same plane iin these first three molecules. Beginning with rings of cyclohexane and larger, the bond angles have the preferred 109.5o bond angle since the all of the carbons are no longer in the same plane.

Cycloalkanes: CnH2n

Name
Molecular Formula
Chemical Structure
Space-Filled Drawing
(Click for large view)
cyclopropane
C3H6
cyclopropane
cyclopropane
cyclobutane
C4H8
cyclobutane
cyclobutane
cyclopentane
C5H10
cyclopentane
cyclopentane
cyclohexane
C6H12
cyclohexane
cyclohexane
cycloheptane
C7H14
cycloheptane
cycloheptane
cyclooctane
C8H16
cyclooctane
cyclooctane
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Updated on: April 15, 2010 8:26 PM