12 2 Alkanes A large number of carbon

12. 2 Alkanes A large number of carbon compounds are possible because the covalent bonds between carbon atoms, such as those in propane (C 3 H 8), are very strong, allowing carbon atoms to form long, stable chains Learning Goal Write the IUPAC names and draw the condensed structural formulas and skeletal formulas for alkanes and cycloalkanes. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Alkanes • are formed by a continuous chain of carbon atoms. • are named using the IUPAC (International Union of Pure and Applied Chemistry) system. • have names that end in ane. • use Greek prefixes to name carbon chains with five or more carbon atoms. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

IUPAC Names of Alkanes with five or more carbon atoms in a chain are named using Greek prefixes: pent (5), hex (6), hept (7), oct (8), non (9), and dec (10). General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Condensed Structural Formulas In a condensed structural formula, • each carbon atom and its attached hydrogen atoms are written as a group. • a subscript indicates the number of hydrogen atoms bonded to each carbon atom. Core Chemistry Skill Naming and Drawing Alkanes General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Line-Angle Structural Formulas A simplified structure of organic molecules • is called the line-angle structural formula. • shows a zigzag line in which carbon atoms are represented as the ends of each line and as corners. Carbon atoms • at the end are bonded to three hydrogen atoms. • in the middle are bonded to two hydrogen atoms. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Guide to Drawing Structural Formulas for Alkanes General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Drawing Expanded, Condensed, and Line. Angle Structural Formulas Draw the expanded, condensed, and line-angle structural formula for pentane. STEP 1 Draw the carbon chain. A molecule of pentane has five carbon atoms in a continuous chain. STEP 2 Draw the expanded structural formula by adding the hydrogen atoms, usingle bonds to each of the carbon atoms. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Drawing Expanded, Condensed, and Line. Angle Structural Formulas Draw the expanded, condensed, and line-angle structural formula for pentane. STEP 3 Draw the condensed structural formula by combining the H atoms with each C atom. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Drawing Expanded, Condensed, and Line. Angle Structural Formulas Draw the expanded, condensed, and line-angle structural formula for pentane. STEP 4 Draw the line-angle structural formula as a zigzag line in which the ends and corners represent C atoms. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Conformations of Alkanes Carbon atoms in a chain, connected by single C — C bonds • can rotate so that groups attached to each carbon move freely about the C — C bond. • can have different arrangements known as conformations. As the — CH 3 groups rotate about the single C — C bond, they appear at different angles. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Structural Formulas: C 4 H 10 As butane (C 4 H 10) rotates, sometimes the — CH 3 groups line up in front of each other, and at other times they are opposite each other. Butane can be drawn using a variety of twodimensional condensed structural formulas: General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Cycloalkanes • are cyclic alkanes. • have two fewer hydrogen atoms than the open chain form. • are named by using the prefix cyclo before the name of the alkane chain with the same number of carbon atoms. propane (C 3 H 8) cyclopropane (C 3 H 6) General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Formulas of Cycloalkanes General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Study Check Give the IUPAC name for each of the following compounds: A. B. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Solution Give the IUPAC name for each of the following compounds: A. an alkane with eight continuous carbon atoms is octane. B. A cyclic molecule with five carbons is cyclopentane. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Study Check Name the following alkanes: A. CH 3−CH 2−CH 3 B. C. CH 3−CH 2−CH 2−CH 3 D. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

Solution Name the following alkanes: A. CH 3−CH 2−CH 3 butane B. cyclopropane C. CH 3−CH 2−CH 2−CH 3 octane D. cyclohexane General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.