1. Introduction to Alkanes: Methane, Ethane, and Propane
CnH2n+2
Introduction to Alkanes: Methane, Ethane, and Propane 21

2. The Simplest Alkanes Methane (CH4) CH4 Ethane (C2H6) CH3CH3
Propane (C3H8) CH3CH2CH3
bp -160°C
bp -89°C
bp -42°C 22

3. Isomeric Alkanes: The Butanes
C4H10
Isomeric Alkanes: The Butanes 21

4. n-Butane CH3CH2CH2CH3
Isobutane (CH3)3CH
bp -0.4°C
bp -10.2°C 23

5. Higher n-Alkanes 21

6. CH3CH2CH2CH2CH3 n-Pentane CH3CH2CH2CH2CH2CH3 n-Hexane
CH3CH2CH2CH2CH2CH2CH3
n-Heptane 24

7. The C5H12 Isomers 21

8. C5H12 CH3CH2CH2CH2CH3 (CH3)2CHCH2CH3 n-Pentane Isopentane (CH3)4C
Neopentane 25

9. How many isomers?
The number of isomeric alkanes increases as the number of carbons increase.
There is no simple way to predict how many isomers there are for a particular molecular formula.

10. Number of Constitutionally Isomeric AlkanesCH
C2H
C3H
C4H
C5H
C6H
C7H
C8H18 18
C9H20 35
C10H22 75
C15H32 4,347
C20H ,319
C40H82 62,491,178,805,831 27

11. Systematic Nomenclature
International Union of Pure and Applied Chemistry
IUPAC
Committee on Organic Nomenclature

12. The alkanes

13. Nomenclature of the Alkanes
Alkanes always have the ending -ane.
Side chains (substituents) are named as alkyl groups.

14. Common alkyl groups (C1 through C4)

15. IUPAC nomenclature of alkanes
identify the longest chain -- parent
number from the end closest to first branch
Name the groups attached to the chain, using the carbon number as the locator.
Alphabetize substituents.
Use di-, tri-, etc., for multiples of same substituent
combine number and name of substituent with parent name, separating with hyphen

16. Longest Chain
The number of carbons in the longest chain determines the base name: ethane, hexane.
If there are two possible chains with the same number of carbons, use the chain with the most substituents.
=>

17. Number the Carbons
Start at the end closest to the first attached group.
If two substituents are equidistant, look for the next closest group. 1 2 3 4 5 6 7

18. Organic nomenclature
2-methylbutane

19. Find the longest continuous carbon chain
3-methylpentane

20. You must choose the longest continuous carbon chain
4-ethylheptane

21. IUPAC rules 1. Find the longest straight chain = parent chain
2. Number the parent chain in the direction that gives the lowest number to the substituents at the first point of difference.
3. Two or more identical groups are indicated by di, tri, tetra, etc.
Longest chain is 7 (not 6).
This is 3-methylheptane. .
2,3,6-trimethylheptane
(not 2,5,6-trimethyl heptane)
2,2,6,6,7-pentamethyloctane
(not 2,3,3,7,7-pentamethyloctane)

22. IUPAC rules
4. Different groups are listed in alphabetical order (di, tri, tetra, etc. don’t count; n, sec, tert don’t count; iso does).
5. If the numbering is the same in both directions, choose the numbering to follow the alphabetical order.
6-ethyl-5-isopropyl-2,2-dimethyloctane
5-ethyl-6-methyldecane

23. IUPAC rules
6. When two or more chains compete for the longest, the choice goes to the one with the greater number of side groups.
2,4,6-trimethyl-5-propyloctane

24. Number from the end nearest the first substituent
4-ethyl-3-methylheptane

25. Number from the end nearest the first substituent
3-ethyl-5-methyloctane

26. Use “di-” with two substituents
2,3-dimethylbutane

27. Every substituent must get a number
3,3-dimethylhexane

28. Number from the end nearest first substituent
2,7,8-trimethyldecane

29. Number from the end which has the “first difference”
3,4,8-trimethyldecane

30. A More-Highly-Substituted Carbon Takes Precedence
2,2,4-Trimethylpentane

31. Which end do we number from?
3-ethyl-6-methyloctane

32. IUPAC rules Name the following compounds.
6-ethyl-2,2,5,7-tetramethylnonane
(not 6,7-diethyl-2,2,5-trimethyloctane.
7-tert-butyl-8-isobutyl-4-isopropyldodecane
(hyphenated words aren’t alphabetized). OR
7-(1,1-dimethylethyl)-4-(1-methylethyl)-
8-(2-methylpropyl)dodecane

33. 7-(1,1-Dimethylbutyl)-3-ethyl-7-methyldodecane
Good Luck!
7-(1,1-Dimethylbutyl)-3-ethyl-7-methyldodecane

34. Branched Substituents
isopropyl
sec-butyl
isobutyl
tert-butyl
(t-butyl)
neo-pentyl

40. Halogens and other side groups
Fluoro –F
Chloro –Cl
Bromo –Br
Iodo –I
Nitro –NO2

41. Bromoethane
“Ethyl bromide”

42. 2-Chloro-2-methylpropane
“tert-Butyl chloride”

43. 2-Bromo-3-methylpentane

44. Complex Substituents
If the branch has a branch, number the carbons from the point of attachment.
Name the branch off the branch using a locator number.
Parentheses are used around the complex branch name. 1 2 3
1-methyl-3-(1,2-dimethylpropyl)cyclohexane =>

45. The isopropyl group can be named as a “complex” substituent
1-methylethyl

46. If you can name this, you can name almost anything!
4-isopropyl-2,6,6-trimethylnonane

47. Now, rename the isopropyl group. Notice the alphabetical order!
2,6,6-trimethyl-4-(1-methylethyl)nonane

48. Naming complex substituents -- this one is alphabetized under d
1,3-dimethylbutyl

49. deciding on alphabetical order for complex groups
Complex groups are alphabetized under the first letter of the name
(1,3-dimethylbutyl) = d
(1,1,2-trimethylpropyl) = t
(1-ethyl-1,2-dimethylbutyl) = e

50. Naming complex substituents
2-ethyl-1,1-dimethylbutyl

51. 5-(1-Ethyl-1-methylpropyl)-5-propylnonane
This Should Be Fun
5-(1-Ethyl-1-methylpropyl)-5-propylnonane

52. name this two ways -- (the complex group)
7-(1,1-dimethylethyl)-3-ethyl-7-methyldecane
7-tert-butyl-3-ethyl-7-methyldecane

53. Common Nomenclature Pitfalls
Did not find the longest carbon chain
Numbered chain from the wrong end
Forgot to repeat number for each identical substituent; forgot to use di- tri- tetra-, etc.
Used “iso”, “sec”, or “tert” as part of a parent name
Confusing propyl / isopropyl, etc.
Writing the name as more than one word
Incorrect punctuation

54. degree of substitution

55. Degree of Substitution
1° ° ° ° ° ° ° ° ° ° ° ° ° ° °

56. Block diagram for nomenclature

57. cyclic molecules

58. Nomenclature for Cyclic Alkanes
For compounds with a single ring, add the prefix “cyclo-” to the root name for the alkane comprising the ring.

59. Nomenclature of the Substituted Cycloalkanes
If there is only one substituent, do not use the “1”.
If there is more than one substituent, you must use all numbers, including “1”!
Number around the ring in a direction to get from the first substituent to the second substituent by the shorter path.
For equivalent degrees of substitution, number in a direction that follows the alphabetical sequence.
A carbon with greater substitution has precedence in numbering.

60. Bromocyclopropane

61. 1,1-Dimethylcyclohexane

62. 4-Ethyl-1,1-dimethylcyclohexane

63. Two ways of naming this 1-isopropyl-2-methylcyclohexane
1-methyl-2-(1-methylethyl)cyclohexane

64. Numbering Starts at the Most Highly-Substituted Carbon2 1 3 7 4 6 5
2-Chloro-1,1,6-trimethylcycloheptane

65. cycloalkyl groups

66. 3-Cyclobutyl-3-methylpentane

67. 2-Cyclobutylbutane
sec-Butylcyclobutane

68. IUPAC rules
Name the following cycloalkanes. Check your answers by clicking on the arrow.
1,1,2-trimethycyclohexane
4-cyclopentyl-2,3-dimethylhexane
1,2-dicyclopropylethane