HOAÙ HOÏC HÖÕU CÔ

1. HOAÙ HOÏC HÖÕU CÔ CHÖÔNG 10 HÔÏP CHAÁT CARBONYL ALDEHYD VAØ CETON Organic Chemistry

2. Aldehydes and Ketones • Aldehydes and ketones are characterized by the the carbonyl functional group (C=O) • The compounds occur widely in nature as intermediates in metabolism and biosynthesis • They are also common as chemicals, as solvents, monomers, adhesives, agrichemicals and pharmaceuticals

3. DANH PHAÙP • Several functional groups contain the carbonyl group • The carbonyl carbon: sp2 hybridized and trigonal planar

4. Naming Aldehydes and Ketones • Aldehydes are named by replacing the terminal -e of the corresponding alkane name with –al • The parent chain must contain the CHO group • The CHO carbon is numbered as C1 • If the CHO group is attached to a ring, use the suffix See Table 19.1 for common names

5. Nomenclature - Aldehydes • IUPAC names: select as the parent alkane the longest chain of carbon atoms that contains the carbonyl group • because the carbonyl group of the aldehyde must be on carbon 1, there is no need to give it a number • For unsaturated aldehydes, show the presence of the C=C by changing the infix -an- to -en- • the location of the suffix determines the numbering pattern

6. Nomenclature - Aldehydes

7. DANH PHAÙP

8. Nomenclature - Aldehydes • For cyclic molecules in which the -CHO group is attached to the ring, the name is derived by adding the suffix -carbaldehydeto the name of the ring

9. DANH PHAÙP

10. DANH PHAÙP

11. Nomenclature - Ketones • IUPAC names: • select as the parent alkane the longest chain that contains the carbonyl group, • changing the suffix -e to -one • number to give C=O the smaller number

12. Naming Ketones • Replace the terminal -e of the alkane name with –one • Parent chain is the longest one that contains the ketone group • Numbering begins at the end nearer the carbonyl carbon

13. DANH PHAÙP

14. Nomenclature - Ketones • The IUPAC system retains these names

15. DANH PHAÙP

16. DANH PHAÙP

17. Ketones and Aldehydes as Substituents • The R–C=O as a substituent is an acyl group is used with the suffix -yl from the root of the carboxylic acid • CH3CO: acetyl; CHO: formyl; C6H5CO: benzoyl • The prefix oxo- is used if other functional groups are present and the doubly bonded oxygen is labeled as a substituent on a parent chain

18. Order of Precedence • For compounds that contain more than one functional group indicated by a suffix

19. DANH PHAÙP

20. DANH PHAÙP

21. IR of Molecules with C=O Groups

22. IR of Molecules with C=O Groups

23. -1 -1 -1 -1 1715 cm 1745 cm 1780 cm 1850 cm -1 -1 -1 1717 cm 1690 cm 1700 cm Carbonyl groups • The position of C=O stretching vibration is sensitive to its molecular environment • as ring size decreases and angle strain increases, absorption shifts to a higher frequency • conjugation shifts the C=O absorption to lower frequency O O O O O O O H

24. 19.2 Preparation of Aldehydes and Ketones • Preparing Aldehydes • Oxidize primary alcohols using pyridinium chlorochromate • Reduce an ester with diisobutylaluminum hydride (DIBAH)

25. Aldehydes and Ketones • IR spectrum of menthone (Fig 12.12)

26. Preparing Ketones • Oxidize a 2° alcohol (see Section 17.8) • Many reagents possible: choose for the specific situation (scale, cost, and acid/base sensitivity)

27. Ketones from Ozonolysis • Ozonolysis of alkenes yields ketones if one of the unsaturated carbon atoms is disubstituted (see Section 7.8)

28. Aryl Ketones by Acylation • Friedel–Crafts acylation of an aromatic ring with an acid chloride in the presence of AlCl3 catalyst (see Section 16.4)

29. Methyl Ketones by Hydrating Alkynes • Hydration of terminal alkynes in the presence of Hg2+ (catalyst: Section 8.5)

30. Introduction • The carbonyl group is polarized • Carbonyl groups can undergo nucleophilic addition • The carbonyl group is an electrophile

31. Relative Reactivity of Aldehydes and Ketones • Aldehydes are generally more reactive than ketones in nucleophilic addition reactions • The transition state for addition is less crowded and lower in energy for an aldehyde (a) than for a ketone (b) • Aldehydes have one large substituent bonded to the C=O: ketones have two

32. Electrophilicity of Aldehydes and Ketones • Aldehyde C=O is more polarized than ketone C=O • As in carbocations, more alkyl groups stabilize + character • Ketone has more alkyl groups, stabilizing the C=O carbon inductively

33. Reactivity of Aromatic Aldehydes • Less reactive in nucleophilic addition reactions than aliphatic aldehydes • Electron-donating resonance effect of aromatic ring makes C=O less reactive electrophilic than the carbonyl group of an aliphatic aldehyde

34. Reaction Theme • One of the most common reaction themes of the carbonyl group is addition of a nucleophile to form a tetrahedral carbonyl addition compound

35. Oxidation and Reduction • Carbonyl groups and alcohols interconverted by oxidation and reduction reactions • Reduction: gain of hydrogen, loss of oxygen, … • Level of oxidation decreases • Oxidation: gain of oxygen, loss of hydrogen, … • Level of oxidation increases

36. Reduction • Any carbonyl compound can be reduced to alcohol

37. Reduction • Reduction of carboxylic acids • With powerful reducing agents such as lithium aluminum hydride (LiAlH4also abbreviated LAH) • LAH is an hydride (H-) source and therefore basic. • H- is also a nucleophile

38. Reduction • Esters, aldehydes and ketones to primary and secondary alcohols

39. Reduction • Esters, aldehydes and ketones to primary and secondary alcohols

40. Reduction • Acids and esters less reactive than ketones and aldehydes • LAH is very reactive with water and must be used in an anhydrous solvent such as ether • NaBH4 is considerably less reactive and can be used in solvents such as water or an alcohol

41. Reduction • An aldehyde can be reduced to a 1° alcohol and a ketone to a 2° alcohol

42. Catalytic Reduction • Catalytic reductions are generally carried out from 25° to 100°C under 1 to 5 atm H2

43. Catalytic Reduction • A carbon-carbon double bond may also be reduced under these conditions • by careful choice of experimental conditions, it is often possible to selectively reduce a carbon-carbon double in the presence of an aldehyde or ketone

44. Metal Hydride Reduction • The most common laboratory reagents for the reduction of aldehydes and ketones are NaBH4 and LiAlH4 • both reagents are sources of hydride ion, H:-, a very powerful nucleophile

45. NaBH4 Reduction • Reductions with NaBH4 are most commonly carried out in aqueous methanol, in pure methanol, or in ethanol • one mol of NaBH4 reduces four mol of aldehyde or ketone

46. NaBH4 Reduction • the key step in metal hydride reduction is transfer of a hydride ion to the C=O group to form a tetrahedral carbonyl addition compound

47. LiAlH4 Reduction • Unlike NaBH4, LiAlH4 reacts violently with water, methanol, and other protic solvents • reductions using this reagent are carried out in diethyl ether or tetrahydrofuran (THF)

48. Metal Hydride Reduction • Metal hydride reducing agents do not normally reduce carbon-carbon double bonds, and selective reduction of C=O or C=C is often possible

49. Reductive Amination • A value of imines is that the carbon-nitrogen double bond can be reduced to a carbon-nitrogen single bond

50. Oxidation • A primary alcohol can be oxidized to an aldehyde or a carboxylic acid • pyridinium chlorochromate (PCC) stops the oxidation at the aldehyde stage