ORGANIC CHEMISTRY

1. ORGANIC CHEMISTRY

2. Types of Organic Compounds • Vast majority of over 20 million known compounds are based on C: organic compounds. • Generally contain C and H + other elements • Great variety of compounds

3. Isomerism • Isomers have identical composition but different structures • Two forms of isomerism • Constitutional (or structural) • Stereoisomerism • Constitutional • Same empirical formula but different atom-to-atom connections • Stereoisomerism • Same atom-to-atom connections but different arrangement in space.

4. Structural Isomers

5. Cis-2-butene Trans-2-butene Stereoisomers: Geometric Geometric isomers can occur when there is a C=C double bond.

6. Stereoisomers: Optical • Optical isomers are molecules with non-superimposable mirror images. • Such molecules are called CHIRAL • Pairs of chiral molecules are enantiomers. • Chiral molecules in solution can rotate the plane of plane polarized light.

7. Chiral Compounds and Polarized Light

8. Stereoisomers Isomers Chirality generally occurs when a C atom has 4 different groups attached. Lactic acid

9. Stereoisomers Isomers Lactic acid isomers are nonsuperimposable

10. Chirality: Handedness in Nature These molecules are non-superimposable mirror images.

11. Chirality: Handedness in Nature These amino acids are non-superimposable mirror images.

12. Stereoisomers in Nature Right- and left-handed seashells The DNA here is right-handed

13. Hydrocarbons • Compounds of C and H • Subgroups: • Alkanes: C-C single bonds • Alkenes: C=C double bonds • Alkynes: carbon-carbon triple bonds • Aromatic: based on benzene

14. Hydrocarbons • Alkanes have the general formula CnH2n+2 • CH4 = methane • C2H6 = ethane • C3H8 = propane • C4H10 = butane • C5H12 = pentane

16. Methane Hydrate, CH4(H2O)x

17. Methane Hydrate, CH4(H2O)x

18. Methane Hydrate, CH4(H2O)x Gas hydrates have been known for many years, and combustion of a sample of methane hydrate is seen on the front cover. Recently, however, vast deposits of methane hydrate were discovered deep within sediments on the floor of the world’s oceans. How these deposits were formed is a mystery. But what is important is their size. It is estimated that the global methane hydrate deposits contain approximately 1013 tons of carbon, or about twice the combined amount in all reserves of coal, oil, and conventional natural gas. Now if scientists and engineers could only solve the problem of extracting the methane conveniently and safely!

19. Hydrocarbons & Structural Isomerism C5H12 has 3 structural isomers. C6H14 has 5 C7H14 has 9 Isomers of C5H12? Note names of isomers

20. Hydrocarbons: Alkanes Alkanes are colorless gases, liquids, and solids Generally unreactive (but undergo combustion) Not polar (or low polarity) and so are not soluble in water.

21. Hydrocarbons: Cycloalkanes All compounds are flexible. Cyclohexane, C6H12, has interconverting “chair” and “boat” forms.

22. Alkenes: Compounds with C=C Double Bonds • How many isomers are possible for a compound with the formula C4H8?

23. Alkenes—Many Occur Naturally

24. Reactions of Alkenes:ADDITION REACTIONS • Alkenes are unsaturated — more bonds can form to the C atoms • Molecules such as Br2, H2, HCl, HBr, and H2O add to the double bond

25. An Addition Reaction Fat placed in Br2 vapor • The fat in bacon is partially unsaturated. The fat adds Br2 to the C=C bonds. • Fats can be “hydrogenated” with H2.

26. An Addition Reaction Fat placed in Br2 vapor

27. An Addition Reaction • Fats can be “hydrogenated” with H2. Peanut butter has partially hydrogenated vegetable oil.

28. Alkynes • Alkynes have carbon-carbon triple bonds. • C2H2: common name = acetylene systematic name = ethyne Preparation: CaC2(s) + H2O(liq) --> C2H2 (g) + Ca(OH)2(s) ∆Hfo(C2H2, g) = +226.7 kJ/mol ∆Hrxn for C2H2 + O2 = –1300 kJ/mol

29. Aromatic Compounds • Benzene, C6H6, in the top 25 chemicals produced in the U.S. • Starting point for hundreds of other compounds.

30. Resonance in Benzene • C6H6 has two resonance structures with alternating double bonds. • The π electrons are delocalized over the ring.

31. Resonance in Benzene • CC bond order is _______________ • C–C single bond = 154 pm C=C bond = 134 pm • CC bonds in benzene = 139 pm π electrons delocalized

32. Other Aromatic Hydrocarbons Toluene Naphthalene

33. TNTtrinitrotoluene Aniline Phenol C6H5NH2 C6H5OH C6H4CH3(NO2)3 Benzene Derivatives

34. Naming Benzene Derivatives 1,4-dimethylbenzene Common name: Para-xylene

35. Reactions of Aromatics • Substitutions — not additions — are typical. AlCl3 is a catalyst. Catalysts typically used in aromatic substitutions.

36. Functional Groups See CD-ROM Screens 11.5 & 11.6

37. Alcohols • Characterized by –OH group • Name: add –ol to name of hydrocarbon Methanol Butanol

38. Structures of Alcohols C3H5OH: how many structural isomers? Naming: Add -ol to name of 3-C hydrocarbon. Indicate position of OH with number.

39. Alcohol Properties • Alcohols are a derivative of water • Many alcohols dissolve in water Methanol dissolves in water. Butanol is NOT soluble in water.

40. “Sterno” • Alcohols burn in air • A mixture of ethanol + calcium acetate = STERNO

41. Ethylene glycol Propylene glycol GLYCOLSAlcohols with Two OH Groups

42. Alcohol ReactionsScreen 11.6 Elimination—the reverse of addition Substitution

43. Sugars: Related to Alcohols • Sugars are carbohydrates, compounds with the formula Cx(H2O)y. What is the difference between a and b D-glucose?

44. Sucrose and Ribose

45. Methylamine Dimethylamine Trimethylamine Amines Alcohols are derivatives of H2O (R–OH) and amines are derivatives of NH3.

46. Cadaverine Pyridine Amines Amines generally have terrible odors!

47. Amines Amines, like NH3, are bases

48. Amines Many natural products and drugs (such as nicotine and cocaine) are bases. H+ Nicotine

49. Compounds with Carbonyl Group Aldehyde Carboxylic acid Ketone

50. Structures of Aldehydes Odors from aldehydes and ketones Cinnamaldehyde