chapter 12 - alkanes chem 2124 – general chemistry ii alfred state college professor bensley

Chapter 12 - Alkanes

CHEM 2124 – General Chemistry II

Alfred State College

Professor Bensley

Chapter 12 Learning Objectives

Identify and draw acyclic alkanes and cycloalkanes.

Identify constitutional isomers. Name alkanes using the IUPAC system of

nomenclature. Predict the physical properties of alkanes. Write equations for the complete and

incomplete combustion of alkanes.

Chapter 12 – Alkanes

•What are alkanes?

•What does the term saturated hydrocarbon mean?

I. Introduction

•What is a cycloalkane?

• Methane is a one carbon alkane.

• Ethane is a two carbon alkane.

Chapter 12 – AlkanesII. Simple Alkanes

• Propane is a three-carbon alkane.

Chapter 12 – Alkanes

Are these both propane?

II. Simple Alkanes

•Butane is a four-carbon alkane.

•Butane and isobutane are isomers of each other.

•What are Constitutional isomers ?

Chapter 12 – Alkanes

II. Simple Alkanes

• Pentane is a five-carbon alkane with three isomers:

Chapter 12 – Alkanes

II. Simple Alkanes

III. Bond Rotation and Skeletal Structures

Chapter 12 – Alkanes

IV. IUPAC Nomenclature (Alkanes)Chapter 12 – Alkanes

• The names of alkanes with substituents have three parts.

• Carbon substituents are called alkyl groups.

• What is it and why do we use IUPAC names?

IUPAC Nomenclature (Alkanes)

•The longest chain may not be written horizontally

•All three examples below have 6 C’s in their longest chain:

HOW TO Name an Alkane Using the IUPAC System

•It does not matter if the chain is straight or has bends.

IUPAC Nomenclature (Alkanes)

HOW TO Name an Alkane Using the IUPAC System

Step [2] Number the atoms in the carbon chain togive the first substituent the lower number.

CORRECT INCORRECT

IUPAC Nomenclature (Alkanes)

HOW TO Name an Alkane Using the IUPAC System

Step [3] Name and number the substituents.

•Name the substituents as alkyl groups.

•Use the numbers from step [2] to designate their location.

IUPAC Nomenclature (Alkanes)

HOW TO Name an Alkane Using the IUPAC System

•Every carbon belongs to either the longest chain or a substituent, but not both.

•Each substituent needs its own number.

•If two or more substituents are identical, use prefixes to indicate how many.

# of Substituents Prefix2

3

4

di-

tri-

tetra-

IUPAC Nomenclature (Alkanes)

HOW TO Name an Alkane Using the IUPAC System

•The following compound contains two methyl groups, so we use the name dimethyl for them.

IUPAC Nomenclature (Alkanes)

HOW TO Name an Alkane Using the IUPAC System

Step [4] Combine substituent names and numbers + parent + suffix.

•Alphabetize the substituents, ignoring prefixes.

•Precede the name of each substituent by the number that indicates its location.

•There must be one number for each substituent.

•Separate numbers by commas and separate numbers from letters by dashes.

IUPAC Nomenclature (Alkanes)

HOW TO Name an Alkane Using the IUPAC System

CH3 CH CH2 CH2 CH2 CH3

CH3

longest chain is 6 C’s = hexane

1 2

CH3

methyl at C2

2-methylhexane

IUPAC Nomenclature (Alkanes)

HOW TO Name an Alkane Using the IUPAC System

CH3 CH CH CH2 CH2 CH3

CH3

longest chain is 6 C’s = hexane

1 2

CH3

methyl at C2

2,3-dimethylhexane

CH3CH3 methyl at C33

IUPAC Nomenclature (Alkanes)

Sample Problem

Give the IUPAC name for the following compound.

CH3 C CH2CH2 C C CH2CH3

CH3

CH3H H

HCH3CH2

longest chain is 8 C’s = octane1 2 5 6

CH3methyl atC2

CH3 methyl at C6

CH3CH2ethyl at C5

5-ethyl-2,6-dimethyloctane

Chapter 12 – AlkanesV. Cycloalkanes

Chapter 12 – Alkanes

VI. Alkane Physical Properties

Chapter 12 – Alkanes

VII. Applications of Alkanes

Chapter 12 – Alkanes

VIII. Alkane Reactions