Alkanes Chapter 12 Alkanes

2 Alkanes Alkanes: Contain only C and H. Have only single C—C bonds. Have a general formula of C n H 2n +2. C AtomsH AtomsFormula 12(1) + 2 = 4 CH 4 32(3) + 2 = 8 C 3 H 8 62(6) + 2 = 14 C 6 H 14

3 Structural formulas show the arrangement of atoms in an organic compound. In expanded structural formulas, all the individual bonds are drawn. In condensed structural formulas, each carbon is written with the H atoms connected to it. H H | | H—C— = CH 3 — —C— = —CH 2 — | | H H Structural Formulas

4 Line-Bond Formulas Because each C atom has a tetrahedral arrangement, the geometrical arrangement of carbon atoms is not a straight line. A line-bond formula abbreviates the carbon chain and shows only the zigzag pattern of bonds from carbon atom to carbon atom.

5 Summary of Formulas

6 IUPAC System of Naming Alkanes The IUPAC (International Union of Pure and Applied Chemistry) establishes the rules for naming organic compounds. Alkanes are named with –ane endings. The first four alkanes are methane, ethane, propane, and butane. The names of longer carbon chains use Greek prefixes such as pent- for 5 C atoms and hex- for 6 C atoms.

7 Names of Continuous-Chain Alkanes

8 Conformations As the groups attached to a C-C single bond rotate around the bond, their relative arrangements has different conformations.

9 Conformations of Butane Rotation of the end CH 3 - provides different conformations for butane.

10 Drawing Structures for Butane