2.11 IUPAC Nomenclature of Unbranched Alkanes

1. 2.11IUPAC Nomenclature ofUnbranched Alkanes

2. IUPAC Names of Unbranched Alkanes • Retained: • methane CH4 • ethane CH3CH3 • propane CH3CH2CH3 • butane CH3CH2CH2CH3

3. IUPAC Names of Unbranched Alkanes • Note:n-prefix is not part of IUPAC name of any alkane. • For example: n-butane is "common name" for CH3CH2CH2CH3;butane is "IUPAC name." • Others: • Latin or Greek prefix for number of carbons + ane suffix

4. IUPAC Names of Unbranched Alkanes • Number of carbons Name Structure • 5 pentane CH3(CH2)3CH3 • 6 hexane CH3(CH2)4CH3 • 7 heptane CH3(CH2)5CH3 • 8 octane CH3(CH2)6CH3 • 9 nonane CH3(CH2)7CH3 • 10 decane CH3(CH2)8CH3

5. IUPAC Names of Unbranched Alkanes • Number of carbons Name Structure • 11 undecane CH3(CH2)9CH3 • 12 dodecane CH3(CH2)10CH3 • 13 tridecane CH3(CH2)11CH3 • 14 tetradecane CH3(CH2)12CH3 • 15 pentadecane CH3(CH2)7CH3 • 16 hexadecane CH3(CH2)8CH3

6. 2.12Applying the IUPAC Rules:The Names of the C6H14 Isomers

7. The C6H14 Isomers CH3CH2CH2CH2CH2CH3 (CH3)2CHCH2CH2CH3 (CH3CH2)2CHCH3 (CH3)2CHCH(CH3)2 (CH3)3CCH2CH3

8. The C6H14 Isomers CH3CH2CH2CH2CH2CH3 • The IUPAC name of the unbranched alkanewith a chain of 6 carbons is hexane. Hexane

9. IUPAC Nomenclature of Branched Alkanes • Step 1) Find the longest continuous carbonchain and use the IUPAC name of theunbranched alkane as the basis. • Step 2) Add name of substituent as a prefix. • Step 3) Number the chain from the end nearestthe substituent, and identify the carbon to which the substituent is attached by number.

10. The C6H14 Isomers (CH3)2CHCH2CH2CH3 2-Methylpentane (CH3CH2)2CHCH3 3-Methylpentane

11. The C6H14 Isomers (CH3)2CHCH(CH3)2 • Use replicating prefixes (di-, tri-, tetra-, etc.) according to the number of identical substituentsattached to the main chain. 2,3-Dimethylbutane (CH3)3CCH2CH3 2,2-Dimethylbutane

12. 2.13Alkyl Groups

13. H CH3 H C H H H H CH3CH2 C C H H Methyl and Ethyl Groups or Methyl or Ethyl

14. R H R Unbranched Alkyl Groups • If potential point of attachment is at the endof the chain, take the IUPAC name of thecorresponding unbranched alkane and replacethe -ane ending by -yl.

15. R H R H H H H H CH3CH2CH2CH2 C C C C H H H H Unbranched Alkyl Groups • If potential point of attachment is at the endof the chain, take the IUPAC name of thecorresponding unbranched alkane and replacethe -ane ending by -yl. or Butyl

16. CH3(CH2)4CH2 CH3(CH2)5CH2 CH3(CH2)16CH2 Unbranched Alkyl Groups Hexyl Heptyl Octadecyl

17. The C3H7 Alkyl Groups H H H or H CH3CH2CH2 C C C H H H and H H H or H CH3CHCH3 C C C H H H

18. The C3H7 Alkyl Groups H H H • IUPAC name: Propyl • Common name: n-Propyl or H CH3CH2CH2 C C C H H H

19. Naming Alkyl Groups (Table 2.7) • Step 1: Identify longest continuous chain starting at point of attachment. • Step 2: Drop -ane ending from name of unbranched alkane having same number of carbons as longest continuous chain and replace by -yl. • Step 3: Identify substituents on longest continuous chain. • Step 4: Chain is always numbered starting atpoint of attachment.

20. H H H or H CH3CHCH3 H C C C H H The C3H7 Alkyl Groups • IUPAC name: 1-Methylethyl • Common name: Isopropyl

21. H H H or H CH3CH2CH2 C C C H H H The C3H7 Alkyl Groups • Classification: Primary alkyl group • Alkyl groups are classified according to thedegree of substitution at the carbon that bears thepoint of attachment. A carbon that is directlyattached to one other carbon is a primary carbon.

22. H H H or H CH3CHCH3 H C C C H H The C3H7 Alkyl Groups • Classification: Secondary alkyl group • Alkyl groups are classified according to thedegree of substitution at the carbon that bears thepoint of attachment. A carbon that is directlyattached to two other carbons is a secondary carbon.

23. H H H H or H CH3CH2CH2CH2 C C C C H H H H The C4H9 Alkyl Groups • IUPAC name: Butyl • Common name: n-Butyl • Classification: Primary alkyl group

24. 1 3 2 The C4H9 Alkyl Groups H H H H • IUPAC name: 1-Methylpropyl • Common name: sec-Butyl • Classification: Secondary alkyl group or H H CH3CHCH2CH3 C C C C H H H

25. CH3 1 3 2 CH3 C CH2 H The C4H9 Alkyl Groups • IUPAC name: 2-Methylpropyl • Common name: Isobutyl • Classification: Primary alkyl group

26. The C4H9 Alkyl Groups • IUPAC name: 1,1-Dimethylethyl • Common name: tert-Butyl • Classification: Tertiary alkyl group CH3 1 2 CH3 C CH3

27. 2.14IUPAC Names of HighlyBranched Alkanes

28. Branched alkanes • Octane

29. Branched alkanes • 4-Ethyloctane

30. Branched alkanes • 4-Ethyl-3-methyloctane List substituents in alphabetical order.

31. Branched alkanes • 4-Ethyl-3,5-dimethyloctane List substituents in alphabetical order. But don't alphabetize di-, tri-, tetra-, etc.

32. First Point of Difference Rule 5 3 4 6 1 8 7 2 6 2 3 7 4 5 8 1 • The chain is numbered in the direction that gives the lower locant to the substituent at the first point of difference in the names. • Don't add locants! What is correct name? 2,3,3,7,7-Pentamethyloctane? 2,2,6,6,7-Pentamethyloctane?

33. First Point of Difference Rule 5 3 1 7 6 2 4 8 • The chain is numbered in the direction that gives the lower locant to the substituent at the first point of difference in the names. • Don't add locants! What is correct name? 2,2,6,6,7-Pentamethyloctane?

34. 2.15Cycloalkane Nomenclature CnH2n

35. Cycloalkanes • Cycloalkanes are alkanes that contain a ring of three or more carbons. • Count the number of carbons in the ring, and add the prefix cyclo to the IUPAC name of the unbranched alkane that has that number of carbons. Cyclopentane Cyclohexane

36. CH2CH3 Cycloalkanes • Name any alkyl groups on the ring in the usual way. Ethylcyclopentane

37. H3C CH3 CH2CH3 Cycloalkanes • Name any alkyl groups on the ring in the usual way. • List substituents in alphabetical order and countin the direction that gives the lowest numericallocant at the first point of difference. 3-Ethyl-1,1-dimethylcyclohexane

38. 2.16Sources of Alkanes and Cycloalkanes

39. Crude oil

40. Crude oil Naphtha (bp 95-150 °C) Kerosene (bp: 150-230 °C) C5-C12 C12-C15 Light gasoline (bp: 25-95 °C) C15-C25 Gas oil (bp: 230-340 °C) Refinery gas C1-C4 Residue

41. Petroleum Refining • Cracking • converts high molecular weight hydrocarbons to more useful, low molecular weight ones • Reforming • increases branching of hydrocarbon chainsbranched hydrocarbons have better burningcharacteristics for automobile engines

42. 2.17Physical Properties of Alkanesand Cycloalkanes

43. Boiling Points of Alkanes • governed by strength of intermolecular attractive forces • alkanes are nonpolar, so dipole-dipole and dipole-induced dipole forces are absent • only forces of intermolecular attraction are induced dipole-induced dipole forces

44. Induced dipole-Induced dipole attractive forces • two nonpolar molecules • center of positive charge and center of negative charge coincide in each + – + –

45. Induced dipole-Induced dipole attractive forces • movement of electrons creates an instantaneous dipole in one molecule (left) + – + –

46. Induced dipole-Induced dipole attractive forces • temporary dipole in one molecule (left) induces a complementary dipole in other molecule (right) – + – +

47. Induced dipole-Induced dipole attractive forces • temporary dipole in one molecule (left) induces a complementary dipole in other molecule (right) – – + +

48. Induced dipole-Induced dipole attractive forces • the result is a small attractive force between the two molecules – – + +

49. Induced dipole-Induced dipole attractive forces • the result is a small attractive force between the two molecules – – + +

50. Boiling Points • increase with increasing number of carbons • more atoms, more electrons, more opportunities for induced dipole-induced dipole forces • decrease with chain branching • branched molecules are more compact with smaller surface area—fewer points of contact with other molecules