Chapter 25 Organic and Biological Chemistry

1. Chapter 25Organic and Biological Chemistry

5. Calculate grade: • (Add exam1 - exam 4 scores)X1.5 • (Add 7 best quizzes)X1.42 • Gives you the # points you have so far. • Final (worth 200 points) • Grades: • 800 - 4 • 750 - 3.5 • 700 - 3 • 650 - 2.5 • 600 - 2.0 etc.

6. Organic Chemistry • The chemistry of carbon compounds. • What’s special about carbon? • tetravalent (sp3 hybridization) • wide choice in oxidation states • CO2 C, +4 • CH4 C, -4 • bonds well to O,N,halides,itself,etc.

7. Structure of Carbon Compounds • There are three hybridization states and geometries found in organic compounds: • sp3Tetrahedral • sp2 Trigonal planar • sp Linear

8. Hydrocarbons • Four types: • Alkanes • Alkenes • Alkynes • Aromatic hydrocarbons

9. Alkanes • Only single bonds. • Saturated hydrocarbons. • “Saturated” with hydrogens.

10. Formulas • Lewis structures of alkanes look like this. • Also called structural formulas. • Often not convenient, though…

11. Formulas …so more often condensed formulas are used.

12. Properties of Alkanes • Only van der Waals force: London force. • Boiling point increases with length of chain.

13. Structure of Alkanes • Carbons in alkanes sp3 hybrids. • Tetrahedral geometry. • 109.5° bond angles.

14. Structure of Alkanes • Only -bonds in alkanes • Free rotation about C—C bonds.

15. Isomers Have same molecular formulas, but atoms are bonded in different order.

16. Organic Nomenclature • Three parts to a compound name: • Base: Tells how many carbons are in the longest continuous chain.

17. Organic Nomenclature • Three parts to a compound name: • Base: Tells how many carbons are in the longest continuous chain. • Suffix: Tells what type of compound it is.

18. Organic Nomenclature • Three parts to a compound name: • Base: Tells how many carbons are in the longest continuous chain. • Suffix: Tells what type of compound it is. • Prefix: Tells what groups are attached to chain.

19. To Name a Compound… • Find the longest chain in the molecule. • Number the chain from the end nearest the first substituent encountered. • List the substituents as a prefix along with the number(s) of the carbon(s) to which they are attached.

20. To Name a Compound… If there is more than one type of substituent in the molecule, list them alphabetically.

21. Cycloalkanes • Carbon can also form ringed structures. • Five- and six-membered rings are most stable. • Can take on conformation in which angles are very close to tetrahedral angle. • Smaller rings are quite strained.

22. For the Quiz • Problems: 7, 10, 17, 21, 23, 25, 37 • Of interest for the final: • 39,40,43,45,47,49,55,61,63,65,97 • All of this is of course now on the web. I’ll put the chap 5 notes on the web as well today, though they are not “perfected” yet.

23. Reactions of Alkanes • Rather unreactive due to presence of only C—C and C—H -bonds. • Therefore, great nonpolar solvents. • General rule of organic chemistry; • reactivity comes from the functional groups, ie. the part of the molecule that is not a straight alkane. • different functional groups give rise to different kinds of activity.

24. Alkenes • Contain at least one carbon–carbon double bond. • Unsaturated. • Have fewer than maximum number of hydrogens.

25. Structure of Alkenes • Unlike alkanes, alkenes cannot rotate freely about the double bond. • Side-to-side overlap makes this impossible without breaking -bond.

26. Structure of Alkenes This creates geometric isomers, which differ from each other in the spatial arrangement of groups about the double bond.

27. Properties of Alkenes Structure also affects physical properties of alkenes.

28. Nomenclature of Alkenes • Chain numbered so double bond gets smallest possible number. • cis- alkenes have carbons in chain on same side of molecule. • trans- alkenes have carbons in chain on opposite side of molecule.

29. Reactions of Alkenes • Addition Reactions • Two atoms (e.g., bromine) add across the double bond. • One -bond and one -bond are replaced by two -bonds; therefore, H is negative.

30. Mechanism of Addition Reactions • The basics of arrrow pushing: • Two-step mechanism: • First step is slow, rate-determining step. • Second step is fast.

31. Mechanism of Addition Reactions In first step, -bond breaks and new C—H bond and cation form.

32. Mechanism of Addition Reactions In second step, new bond forms between negative bromide ion and positive carbon.

33. Alkynes • Contain at least one carbon–carbon triple bond. • Carbons in triple bond sp-hybridized and have linear geometry. • Also unsaturated.

34. Nomenclature of Alkynes 4-methyl-2-pentyne • Analogous to naming of alkenes. • Suffix is -yne rather than –ene.

35. Reactions of Alkynes • Undergo many of the same reactions alkenes do. • As with alkenes, impetus for reaction is replacement of -bonds with -bonds.

36. Aromatic Hydrocarbons • Cyclic hydrocarbons. • p-Orbital on each atom. • Molecule is planar. • Odd number of electron pairs in -system.

37. Aromatic Nomenclature Many aromatic hydrocarbons are known by their common names.

38. Reactions of Aromatic Compounds • Unlike in alkenes and alkynes, -electrons do not sit between two atoms. • Electrons are delocalized; this stabilizes aromatic compounds.

39. Reactions of Aromatic Compounds • Due to stabilization, aromatic compounds do not undergo addition reactions; they undergo substitution. • Hydrogen is replaced by substituent.

40. Structure of Aromatic Compounds • Two substituents on a benzene ring could have three possible relationships • ortho-: On adjacent carbons. • meta-: One carbon between them. • para-: On opposite sides of ring.

41. Reactions of Aromatic Compounds Halogenation Reactions of aromatic compounds often require a catalyst. Friedel-Crafts Reaction

42. Functional Groups Term used to refer to parts of organic molecules where reactions tend to occur.

43. Alcohols • Contain one or more hydroxyl groups, —OH • Named from parent hydrocarbon; suffix changed to -ol and number designates carbon to which hydroxyl is attached.

44. Alcohols a steroid

45. Ethers • Tend to be quite unreactive. • Therefore, they are good polar solvents.

46. Carbonyl Compounds • Contain C—O double bond. • Include many classes of compounds.

47. Aldehydes At least one hydrogen attached to carbonyl carbon.

48. Ketones Two carbons bonded to carbonyl carbon.

49. Carboxylic Acids • Have hydroxyl group bonded to carbonyl group. • Tart tasting. • Carboxylic acids are weak acids. CH3COOH

50. Carboxylic Acids