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