Chapter 12 - Alkanes

1. Chapter 12 - Alkanes CHEM 2124 – General Chemistry II Alfred State College Professor Bensley

2. 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.

3. Chapter 12 – Alkanes I. Introduction • What are alkanes? • What does the term saturatedhydrocarbon mean? • What is a cycloalkane?

4. Chapter 12 – Alkanes II. Simple Alkanes • Methane is a one carbon alkane. • Ethane is a two carbon alkane.

5. Chapter 12 – Alkanes II. Simple Alkanes • Propane is a three-carbon alkane. Are these both propane?

6. Chapter 12 – Alkanes II. Simple Alkanes • Butane is a four-carbon alkane. • Butane and isobutane are isomers of each other. • What are Constitutional isomers ?

7. Chapter 12 – Alkanes II. Simple Alkanes • Pentane is a five-carbon alkane with three isomers:

9. Chapter 12 – Alkanes III. Bond Rotation and Skeletal Structures

10. Chapter 12 – Alkanes IV. IUPAC Nomenclature (Alkanes) • What is it and why do we use IUPAC names? • The names of alkanes with substituents have three parts. • Carbon substituents are called alkyl groups.

12. IUPAC Nomenclature (Alkanes) HOW TO Name an Alkane Using the IUPAC System • The longest chain may not be written horizontally • It does not matter if the chain is straight or has bends. • All three examples below have 6 C’s in their longest chain:

13. IUPAC Nomenclature (Alkanes) HOW TO Name an Alkane Using the IUPAC System Number the atoms in the carbon chain to give the first substituent the lower number. Step [2] INCORRECT CORRECT

14. 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.

15. 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 Prefix 2 di- tri- 3 4 tetra-

16. 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.

17. IUPAC Nomenclature (Alkanes) HOW TO Name an Alkane Using the IUPAC System Combine substituent names and numbers + parent + suffix. Step [4] • 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.

18. IUPAC Nomenclature (Alkanes) HOW TO Name an Alkane Using the IUPAC System methyl at C2 CH3 CH3 CH3 CH2 CH2 CH2 CH CH3 1 2 longest chain is 6 C’s = hexane 2-methylhexane

19. IUPAC Nomenclature (Alkanes) HOW TO Name an Alkane Using the IUPAC System methyl at C2 CH3 CH3 CH3 CH CH2 CH2 CH CH3 CH3 CH3 methyl at C3 1 3 2 longest chain is 6 C’s = hexane 2,3-dimethylhexane

20. IUPAC Nomenclature (Alkanes) Sample Problem Give the IUPAC name for the following compound. ethyl at C5 methyl at C2 CH3 CH3 CH3CH2 CH3CH2 H CH3 CH2CH2 C C C CH2CH3 H H CH3 CH3 methyl at C6 1 2 5 6 longest chain is 8 C’s = octane 5-ethyl-2,6-dimethyloctane

21. Chapter 12 – Alkanes V. Cycloalkanes

22. Chapter 12 – Alkanes VI. Alkane Physical Properties • Polarities • Melting and Boiling • Points • Phases of matter • Solubility • Density

23. Chapter 12 – Alkanes VII. Applications of Alkanes

24. Chapter 12 – Alkanes VIII. Alkane Reactions