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1 Thus, 2-cyclohexenone, which contains both a C=C and a C=O, can be reduced to three different compounds depending upon the reagent used. Reduction of.

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Presentation on theme: "1 Thus, 2-cyclohexenone, which contains both a C=C and a C=O, can be reduced to three different compounds depending upon the reagent used. Reduction of."— Presentation transcript:

1 1 Thus, 2-cyclohexenone, which contains both a C=C and a C=O, can be reduced to three different compounds depending upon the reagent used. Reduction of Aldehydes and Ketones Introduction to Carbonyl Chemistry; Organometallic Reagents; Oxidation and Reduction

2 2 Acid chlorides and esters can be reduced to either aldehydes or 1 ° alcohols depending on the reagent.

3 3 Carboxylic acids are reduced to 1° alcohols with LiAlH 4. LiAlH 4 is too strong a reducing agent to stop the reaction at the aldehyde stage, but milder reagents are not strong enough to initiate the reaction in the first place. Reduction of Carboxylic Acids and Their Derivatives Introduction to Carbonyl Chemistry; Organometallic Reagents; Oxidation and Reduction

4 4 Unlike the LiAlH 4 reduction of all other carboxylic acid derivatives, which affords 1° alcohols, the LiAlH 4 reduction of amides forms amines. Reduction of Carboxylic Acids and Their Derivatives Since ¯ NH 2 is a very poor leaving group, it is never lost during the reduction, and therefore an amine is formed. Introduction to Carbonyl Chemistry; Organometallic Reagents; Oxidation and Reduction

5 5 Reduction of Carboxylic Acids and Their Derivatives Introduction to Carbonyl Chemistry; Organometallic Reagents; Oxidation and Reduction

6 6 A variety of oxidizing agents can be used, including CrO 3, Na 2 Cr 2 O 7, K 2 Cr 2 O 7, and KMnO 4. Aldehydes can also be oxidized selectively in the presence of other functional groups using silver(I) oxide in aqueous ammonium hydroxide (Tollen’s reagent). Since ketones have no H on the carbonyl carbon, they do not undergo this oxidation reaction. Oxidation of Aldehydes Introduction to Carbonyl Chemistry; Organometallic Reagents; Oxidation and Reduction

7 7 Organometallic reagents are strong bases that readily abstract a proton from water to form hydrocarbons. Organometallic Reagents Similar reactions occur with the O—H proton of alcohols and carboxylic acids, and the N—H protons of amines. Introduction to Carbonyl Chemistry; Organometallic Reagents; Oxidation and Reduction

8 8 Reaction of Organometallic Reagents with Aldehydes and Ketones. This reaction is used to prepare 1°, 2°, and 3° alcohols. Introduction to Carbonyl Chemistry; Organometallic Reagents; Oxidation and Reduction

9 9 Reaction of Organometallic Reagents with Carboxylic Acid Derivatives. Both esters and acid chlorides form 3° alcohols when treated with two equivalents of either Grignard or organolithium reagents. Introduction to Carbonyl Chemistry; Organometallic Reagents; Oxidation and Reduction

10 10 Reaction of Organometallic Reagents with Other Compounds Grignards react with CO 2 to give carboxylic acids after protonation with aqueous acid. This reaction is called carboxylation. The carboxylic acid formed has one more carbon atom than the Grignard reagent from which it was prepared. Introduction to Carbonyl Chemistry; Organometallic Reagents; Oxidation and Reduction

11 11 ,  -Unsaturated Carbonyl Compounds

12 12 Synthesis Introduction to Carbonyl Chemistry; Organometallic Reagents; Oxidation and Reduction Figure 20.8 Conversion of 2–hexanol into other compounds

13 13 Figure 21.7 Specific examples of nucleophilic addition

14 14 The Wittig reaction uses a carbon nucleophile (the Wittig reagent) to form alkenes—the carbonyl group is converted to a C=C. The Wittig Reaction Aldehydes and Ketones—Nucleophilic Addition

15 15 Wittig reagents are synthesized by a two-step procedure. The Wittig Reaction Aldehydes and Ketones—Nucleophilic Addition

16 16 To synthesize the Wittig reagent Ph 3 P=CH 2, use the following two steps: The Wittig Reaction Step [1] Form the phosphonium salt by S N 2 reaction of Ph 3 P: and CH 3 Br. Step [2] Form the ylide by removal of a proton using BuLi as a strong base. Aldehydes and Ketones—Nucleophilic Addition

17 17 The currently accepted mechanism of the Wittig reaction involves two steps. The Wittig Reaction Aldehydes and Ketones—Nucleophilic Addition

18 18 An advantage of the Wittig reaction over elimination methods used to synthesize alkenes is that you always know the location of the double bond—the Wittig reaction always gives a single constitutional isomer. Consider the two methods that can be used to convert cyclohexanone into cycloalkene B. The Wittig Reaction Aldehydes and Ketones—Nucleophilic Addition

19 19 Because the N atom of an imine is surrounded by three groups (two atoms and a lone pair), it is sp 2 hybridized, making the C—N—R bond angle 120°, (not 180°). Imine formation is fastest when the reaction medium is weakly acidic (pH 4-5). Addition of 1 ° Amines—Formation of Imines Aldehydes and Ketones—Nucleophilic Addition

20 20 Addition of 1 ° Amines—Formation of Imines Aldehydes and Ketones—Nucleophilic Addition

21 21 Aldehydes and Ketones—Nucleophilic Addition Figure 21.9 The key reaction in the chemistry of vision

22 22 A 2° amine reacts with an aldehyde or ketone to give an enamine. Enamines have a nitrogen atom bonded to a C—C double bond. Addition of 2 ° Amines—Formation of Enamines Aldehydes and Ketones—Nucleophilic Addition

23 23 Addition of 2 ° Amines—Formation of Enamines Aldehydes and Ketones—Nucleophilic Addition Figure The formation of imines and enamines compared

24 24 Acetals as Protecting Groups To solve this problem, we can use a protecting group to block the more reactive ketone carbonyl. The overall process requires three steps. [1] Protect the interfering functional group—the ketone carbonyl. [2] Carry out the desired reaction. [3] Remove the protecting group. Aldehydes and Ketones—Nucleophilic Addition

25 25 Cyclic Hemiacetals Hemiacetal formation is catalyzed by both acid and base. Aldehydes and Ketones—Nucleophilic Addition

26 1)Give the IUPAC name for each compound. a) 3,3’-dimethylhexanoic acid b) 4-chloropetanoic acid c) 2,4-diethylhexanoic acid

27 d) 4-isopropyl-6,8-dimethylnonanic acid

28 2)Draw the structure corresponding to the IUPAC name. a) 2-bromobutanoic acid b) 2,3-dimethylpentanoic acid c) 3,3’,4-trimethylheptanoic acid

29 d) 2-secbutyl-4,4’-diethylnonanoic acid e) 3,4-diethylcyclohexanecarboxylic acid

30 f) 1-isopropylcyclobutanecarboxylic acid

31 5) Give the IUPAC name for each metal salt. a)C 6 H 5 CO 2 -+ Li c) (CH 3 ) 2 CHCO 2 -+ K b) HCO 2 -+ Na Lithium benzoate Sodium methanoate Potassium 2-methylpropanoate

32 d) (CH 3 CH 2 ) 2 CHCH 2 CHBrCH 2 CH 2 CO 2 -+ Na Sodium 4-bromo-6-ethyloctanoate

33 7) Explain how you would distinguish between these compounds using IR spectroscopy. 2 peaks C=O OH peak C=O peak -OH

34 8)Propose a compound with the formula, C 4 H 8 O 2 and the following date: 0.95 (triplet, 3H) 1.65 (multiplet, 2H) 2.30 (triplet, 2H) 11.8 (singlet, 1H)

35 11)Identify the starting material in each reaction. a) b) c)

36 d)


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