Chapter 4 Alcohols and Alkyl Halides

1. Chapter 4Alcohols and Alkyl Halides

2. Overview of Chapter This chapter introduces chemical reactions and their mechanisms by focusing on two reactionsthat yield alkyl halides. • (1) alcohol + hydrogen halide • ROH + HX  RX + H2O • (2) alkane + halogen • RH + X2 RX + HX • Both are substitution reactions

3. Functional Groups

4. Functional Group • a structural unit in a molecule responsible for itscharacteristic behavior under a particular set ofreaction conditions

5. Families of organic compoundsand their functional groups • Alcohol ROH • Alkyl halide RX (X = F, Cl, Br, I) • Amine primary amine: RNH2 • secondary amine: R2NH • tertiary amine: R3N

6. C C O Families of organic compoundsand their functional groups • Ether ROR' • Nitrile RCN • Nitroalkane RNO2 • Sulfide RSR' • Thiol RSH Epoxide

7. O O C C Many classes of organic compounds contain a carbonyl group R Carbonyl group Acyl group

8. O O C C Many classes of organic compounds contain a carbonyl group H R Carbonyl group Aldehyde

9. O O C C Many classes of organic compounds contain a carbonyl group R' R Carbonyl group Ketone

10. O O C C Many classes of organic compounds contain a carbonyl group OH R Carbonyl group Carboxylic acid

11. O O C C Many classes of organic compounds contain a carbonyl group OR' R Ester Carbonyl group

12. O O C C Many classes of organic compounds contain a carbonyl group NH2 R Amide Carbonyl group

13. IUPAC Nomenclatureof Alkyl Halides

14. IUPAC Nomenclature There are several kinds of IUPAC nomenclature. • The two that are most widely used are:functional class nomenclaturesubstitutive nomenclature • Both types can be applied to alcohols andalkyl halides.

15. CH3CH2CHCH2CH2CH3 H I Br Functional Class Nomenclature of Alkyl Halides • Name the alkyl group and the halogen asseparate words (alkyl + halide) CH3F CH3CH2CH2CH2CH2Cl

16. CH3CH2CHCH2CH2CH3 H I Br Functional Class Nomenclature of Alkyl Halides • Name the alkyl group and the halogen asseparate words (alkyl + halide) CH3F CH3CH2CH2CH2CH2Cl Methyl fluoride Pentyl chloride 1-Ethylbutyl bromide Cyclohexyl iodide

17. CH3CHCH2CH2CH3 Br CH3CH2CHCH2CH3 I Substitutive Nomenclature of Alkyl Halides • Name as halo-substituted alkanes. • Number the longest chain containing thehalogen in the direction that gives the lowestnumber to the substituted carbon. CH3CH2CH2CH2CH2F

18. CH3CHCH2CH2CH3 Br CH3CH2CHCH2CH3 I Substitutive Nomenclature of Alkyl Halides • Name as halo-substituted alkanes. • Number the longest chain containing thehalogen in the direction that gives the lowestnumber to the substituted carbon. CH3CH2CH2CH2CH2F 1-Fluoropentane 2-Bromopentane 3-Iodopentane

19. Cl CH3 CH3 Cl Substitutive Nomenclature of Alkyl Halides • Halogen and alkyl groupsare of equal rank when it comes to numberingthe chain. • Number the chain in thedirection that gives the lowest number to thegroup (halogen or alkyl)that appears first.

20. Cl CH3 CH3 Cl Substitutive Nomenclature of Alkyl Halides 5-Chloro-2-methylheptane 2-Chloro-5-methylheptane

21. IUPAC Nomenclatureof Alcohols

22. CH3 CH3CCH2CH2CH3 OH CH3CHCH2CH2CH2CH3 OH Functional Class Nomenclature of Alcohols • Name the alkyl group and add "alcohol" as aseparate word. CH3CH2OH

23. CH3 CH3CCH2CH2CH3 OH CH3CHCH2CH2CH2CH3 OH Functional Class Nomenclature of Alcohols • Name the alkyl group and add "alcohol" as aseparate word. CH3CH2OH Ethyl alcohol 1,1-Dimethylbutylalcohol 1-Methylpentyl alcohol

24. CH3 CH3CCH2CH2CH3 OH CH3CHCH2CH2CH2CH3 OH Substitutive Nomenclature of Alcohols • Name as "alkanols." Replace -e ending of alkanename by -ol. • Number chain in direction that gives lowest numberto the carbon that bears the —OH group. CH3CH2OH

25. CH3 CH3CCH2CH2CH3 OH CH3CHCH2CH2CH2CH3 OH Substitutive Nomenclature of Alcohols • Name as "alkanols." Replace -e ending of alkanename by -ol. • Number chain in direction that gives lowest numberto the carbon that bears the —OH group. CH3CH2OH Ethanol 2-Methyl-2-pentanol 2-Hexanol

26. OH CH3 CH3 OH Substitutive Nomenclature of Alcohols • Hydroxyl groups outrank alkyl groups when it comes to numberingthe chain. • Number the chain in thedirection that gives the lowest number to thecarbon that bears theOH group

27. OH CH3 CH3 OH Substitutive Nomenclature of Alcohols 6-Methyl-3-heptanol 5-Methyl-2-heptanol

28. Classes of Alcoholsand Alkyl Halides

29. Classification • Alcohols and alkyl halides are classified asprimary, 1o secondary, 2o tertiary, 3oaccording to their "degree of substitution." • Degree of substitution is determined by countingthe number of carbon atoms directly attached tothe carbon that bears the halogen or hydroxyl group.

30. CH3 CH3CHCH2CH2CH3 CH3CCH2CH2CH3 Br OH Classification H CH3CH2CH2CH2CH2F OH primary alkyl halide secondary alcohol secondary alkyl halide tertiary alcohol

31. Bonding in Alcoholsand Alkyl Halides

32. H H H H O C Cl C Dipole Moments • alcohols and alkyl halides are polar + H + + – – H H  = 1.9 D  = 1.7 D

33. Dipole Moments • alcohols and alkyl halides are polar  = 1.9 D  = 1.7 D

34. Dipole-Dipole Attractive Forces +  – +  – +  – +  –  – +

35. Dipole-Dipole Attractive Forces +  – +  – +  – +  –  – +

36. Physical Properties of Alcohols and Alkyl Halides:Intermolecular Forces • Boiling point • Solubility in water • Density

37. Effect of Structure on Boiling Point CH3CH2CH3 CH3CH2OH • 44 4846 • -42 -32+78 • 0 1.91.7 CH3CH2F Molecularweight Boilingpoint, °C Dipolemoment, D

38. Effect of Structure on Boiling Point CH3CH2CH3 • 44 • -42 • 0 Molecularweight Boilingpoint, °C Dipolemoment, D Intermolecular forcesare weak. Only intermolecular forces are induced dipole-induced dipole attractions.

39. Effect of Structure on Boiling Point CH3CH2F • 48 • -32 • 1.9 A polar molecule;therefore dipole-dipoleand dipole-induceddipole forces contributeto intermolecular attractions. Molecularweight Boilingpoint, °C Dipolemoment, D

40. Effect of Structure on Boiling Point • 46 • +78 • 1.7 CH3CH2OH Highest boiling point;strongest intermolecularattractive forces. Hydrogen bonding isstronger than other dipole-dipole attractions. Molecularweight Boilingpoint, °C Dipolemoment, D

41. Figure 4.4 Hydrogen bonding in ethanol – + + –

42. Figure 4.4 Hydrogen bonding in ethanol

43. Boiling point increases with increasingnumber of halogens Compound Boiling Point • CH3Cl -24°C • CH2Cl2 40°C • CHCl3 61°C • CCl4 77°C Even though CCl4 is the only compound in this list without a dipole moment, it has the highest boiling point. Induced dipole-induced dipole forces are greatest in CCl4 because it has the greatest number of Cl atoms. Cl is more polarizable than H.

44. But trend is not followed when halogenis fluorine • CH3CH2F -32°C • CH3CHF2 -25°C • CH3CF3 -47°C • CF3CF3 -78°C Compound Boiling Point

45. But trend is not followed when halogenis fluorine • CH3CH2F -32°C • CH3CHF2 -25°C • CH3CF3 -47°C • CF3CF3 -78°C Compound Boiling Point Fluorine is not very polarizable and induced dipole-induced dipole forces decrease with increasing fluorine substitution.

46. Solubility in water • Alkyl halides are insoluble in water. • Methanol, ethanol, isopropyl alcohol arecompletely miscible with water. • The solubility of an alcohol in waterdecreases with increasing number of carbons (compound becomesmore hydrocarbon-like).

47. + – + – + – Figure 4.5 Hydrogen Bonding Between Ethanol and Water

48. Density • Alkyl fluorides and alkyl chlorides areless dense than water. • Alkyl bromides and alkyl iodides are more dense than water. • All liquid alcohols have densities of about 0.8 g/mL.

49. Preparation of Alkyl Halides fromAlcohols and Hydrogen Halides • ROH + HX  RX + H2O

50. least reactive most reactive Reaction of Alcohols with Hydrogen Halides ROH + HX RX + HOH • Hydrogen halide reactivity HF HCl HBr HI