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Chapter 12 Alcohols from Carbonyl Compounds Oxidation-Reduction & Organometallic Compounds.

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Presentation on theme: "Chapter 12 Alcohols from Carbonyl Compounds Oxidation-Reduction & Organometallic Compounds."— Presentation transcript:

1 Chapter 12 Alcohols from Carbonyl Compounds Oxidation-Reduction & Organometallic Compounds

2 Ch Structure of the Carbonyl Group  Carbonyl compounds AldehydeKetone Carboxylic acidEsterAmide

3 Ch  Structure ●Carbonyl carbon: sp 2 hybridized ●Planar structure

4 Ch  Polarization and resonance structure

5 Ch A.Reactions of Carbonyl Compounds with Nucleophiles  One of the most important reactions of carbonyl compounds is nucleophilic addition to the carbonyl group

6 Ch  Two important nucleophiles: ●Hydride ions (from NaBH 4 and LiAlH 4 ) ●Carbanions (from RLi and RMgX)  Another important reactions:

7 Ch  Overall order lowest oxidation state of carbon highest oxidation state of carbon oxidation state

8 Ch Alcohols by Reduction of Carbonyl Compounds (1 o alcohol)

9 Ch A.Lithium Aluminum Hydride  LiAlH 4 (LAH) ●Not only nucleophilic, but also very basic ●React violently with H 2 O or acidic protons (e.g. ROH) ●Usually reactions run in ethereal solvents (e.g. Et 2 O, THF) ●Reduces all carbonyl groups

10 Ch  Examples

11 Ch B.Sodium Borohydride  NaBH 4 ●less reactive and less basic than LiAlH 4 ●can use protic solvent (e.g. ROH) ●reduces only more reactive carbonyl groups (i.e. aldehydes and ketones) but not reactive towards esters or carboxylic acids

12 Ch  Examples

13 Ch C.Overall Summary of LiAlH 4 and NaBH 4 Reactivity ease of reduction reduced by NaBH 4 reduced by LiAlH 4

14 Ch Organometallic Compounds  Compounds that contain carbon-metal bonds are called organometallic compounds

15 Ch Preparation of Organolithium & Organomagnesium Compounds 6A.Organolithium Compounds  Order of reactivity of RX ●RI > RBr > RCl  Preparation of organolithium compounds

16 Ch  Example

17 Ch B.Grignard Reagents  Order of reactivity of RX ●RI > RBr > RCl  Preparation of organomagnesium compounds (Grignard reagents)

18 Ch B.Reactions of Grignard Reagents with Epoxides (Oxiranes)  Grignard reagents react as nucleophiles with epoxides (oxiranes), providing convenient synthesis of alcohols

19 Ch  Via S N 2 reaction

20 Ch  Also work for substituted epoxides

21 Ch C.Reactions of Grignard Reagents with Carbonyl Compounds

22 Ch  Mechanism

23 Ch Alcohols from Grignard Reagents

24 Ch  R, R’ = H (formaldehyde) ●1 o alcohol

25 Ch  R = alkyl, R’ = H (higher aldehydes) ●2 o alcohol

26 Ch  R, R’ = alkyl (ketone) ●3 o alcohol

27 Ch  Reaction with esters ●3 o alcohol

28 Ch  Mechanism

29 Ch  Examples

30 Ch  Examples

31 Ch  Examples

32 Ch  Examples

33 Ch A.How to Plan a Grignard Synthesis  Synthesis of

34 Ch  Method 1 ●Retrosynthetic analysis ●Synthesis

35 Ch  Method 2 ●Retrosynthetic analysis ●Synthesis

36 Ch  Method 3 ●Retrosynthetic analysis ●Synthesis

37 Ch B.Restrictions on the Use of Grignard Reagents  Grignard reagents are useful nucleophiles but they are also very strong bases  It is not possible to prepare a Grignard reagent from a compound that contains any hydrogen more acidic than the hydrogen atoms of an alkane or alkene

38 Ch  A Grignard reagent cannot be prepared from a compound containing an –OH group, an –NH– group, an –SH group, a –CO 2 H group, or an –SO 3 H group  Since Grignard reagents are powerful nucleophiles, we cannot prepare a Grignard reagent from any organic halide that contains a carbonyl, epoxy, nitro, or cyano (–CN) group

39 Ch  Grignard reagents cannot be prepared in the presence of the following groups because they will react with them:

40 Ch C.The Use of Lithium Reagents  Organolithium reagents have the advantage of being somewhat more reactive than Grignard reagents although they are more difficult to prepare and handle

41 Ch D.The Use of Sodium Alkynides  Preparation of sodium alkynides  Reaction via ketones (or aldehydes)

42 Ch Protecting Groups

43 Ch  Retrosynthetic analysis  However

44 Ch  Need to “protect” the –OH group first


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