Aldehydes and Ketones

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Aldehydes and Ketones Nucleophilic Addition to the arbonyl Group Nomenclature IUPA Nomenclature of Aldehydes Base the name on the chain that contains the carbonyl group and replace the -e ending of

1 Aldehydes and Ketones Nucleophilic Addition to the arbonyl Group Nomenclature IUPA Nomenclature of Aldehydes Base the name on the chain that contains the carbonyl group and replace the -e ending of the hydrocarbon with -al. IUPA Nomenclature of Aldehydes IUPA Nomenclature of Aldehydes 4,4-dimethylpentan analal 5-hexen enal or hex-5-enal 2-phenylpropane anedial (keep the -e ending before -dial) when named as a substituent formyl group when named as a suffix carbaldehyde or carboxaldehyde

2 What is the correct IUPA name of the aldehyde at the right? Substitutive IUPA Nomenclature of Ketones A) 2,3-dihydroxypropanol B) 1,2-dihydroxypropanal ) 2,3-dihydroxypropanal D) 2,3-propanediol-1-aldehyde 3 3 Base the name on the chain that contains the carbonyl group and replace -e with -one. Number the chain in the direction that gives the lowest number to the carbonyl carbon. Substitutive IUPA Nomenclature of Ketones Functional lass IUPA Nomenclature of Ketones hexan hexanone or exan-3-one 4-methylcyclohexanone one methyl pentanone or 4-methylpentan-2-one List the groups attached to the carbonyl separately in alphabetical order, and add the word ketone. Functional lass IUPA Nomenclature of Ketones What is the IUPA name for the ketone shown below? ethyl propyl ketone 2 2 benzyl ethyl ketone divinyl ketone A) 5-ethyl-2-methyl-3-hexanone B) 2,5-dimethyl-3-heptanone ) 3,6-dimethyl-5-heptanone D) 2-ethyl-5-methyl-5-hexanone

3 A compound ( 7 14 ) has a strong peak in its I spectrum at 1710 cm -1. Its 1 -NM spectrum consists of 3 singlets in the ratio 9:3:2 at δ1.0, δ2.1, and δ2.3, respectively. Identify this compound. The arbonyl Group Structure, Bonding A) 3-heptanone B) 2,2-dimethyl-3-pentanone ) 4,4-dimethyl-2-pentanone D) 2,4-dimethyl-3-pentanone arbonyl Group of a Ketone is More Stable than that of an Aldehyde heat of combustion 2475 kj/mol 2442 kj/mol Alkyl groups stabilize carbonyl groups the same way they stabilize carbon-carbon double bonds, carbocations, and free radicals. Spread is Greater for Aldehydes and Ketones than for Alkenes 2475 kj/mol 2442 kj/mol eats of combustion of 4 8 isomeric alkenes 3 2 = kj/mol cis- 3 = kj/mol trans- 3 = kj/mol ( 3 ) 2 = kj/mol esonance Description of arbonyl Group Synthesis Aldehydes & Ketones Nucleophiles attack carbon; electrophiles attack oxygen.

4 Synthesis of Aldehydes and Ketones A number of reactions already studied provide efficient synthetic routes to aldehydes and ketones. from alkenes ozonolysis from alkynes hydration (via enol) from arenes Friedel-rafts acylation from alcohols oxidation What combination of reagents will transform 1-butyne into 2- butanone? A) , Zn B) K 2 r 2 7, 2 S 4 ) 2 S 4, gs 4 D) s 4 (cat), ( 3 ) 3, ( 3 ) 3, - eduction & xidation Example aldehydes from carboxylic acids Benzaldehyde from benzoic acid 1. LiAl P or PD, 2 l 2 1. LiAl (81%) (83%) P or PD 2 l 2 eduction Grignard & xidation aldehydes from carboxylic acid esters Ketones from aldehydes 1. DIBAL- (Diisobutyl aluminum hydride) 2. 2 ' or from nitriles -N with DIBAL- 1. 'MgX 2. 3 ' ' P or PD, 2 l 2

5 Which combination of reagents will produce 2-hexanone as the major organic product? Example 3-heptanone from propanal A) 2-hexanol P in 2 l 2 B) 1-hexene 2, 2 S 4, gs 4 ) pentanal methylmagnesium bromide followed by 3 D) All of the above (a-c) will produce 2-hexanone as the major product ( 2 ) 3 MgX ( 2 ) 3 3 (57%) 2 r ( 2 ) 3 3 An alcohol with a molecular formula 7 16 was treated with chromic acid. The product produced 4 signals in its 13 -NM spectrum: one at 210 ppm and 3 others below 50 ppm. Identify the ketone. A) 4-heptanone B) 2,4-dimethyl-3-pentanone ) 4,4-dimethyl-2-pentanone D) 5-methyl-3-hexanone eactions of Aldehydes and Ketones eactions of Aldehydes and Ketones eduction of = to 2 Which compound will be isolated from the synthetic sequence shown below? lemmensen reduction Wolff-Kishner reduction eduction of = to A) B) ) D) Addition of Grignard and organolithium reagents

6 Aldehydes and ketones react with nucleophiles to form addition products: nucleophile addition reactions When a nucleophile encounters a ketone, the site of attack is A) the carbon atom of the cabonyl. B) the oxygen atom of the carbonyl. ) both the carbon and oxygen atoms, with equal probability. D) No attack occurs--ketones do not react with nucleophiles. ydration of Aldehydes and Ketones ydration of Aldehydes and Ketones 2 Substituent Effects on ydration Equilibria Equilibrium onstants and elative ates of ydration = hydrate K % elative rate ' 2 compared to ' 2 = 2 () > = 3 () electronic: steric: alkyl groups stabilize reactants alkyl groups crowd product ( 3 ) 3 = ( 3 ) 2 = ( 3 ) 3 () ( 3 ) 2 ()

7 Equilibrium an Favor a ydrate (But not very often) Substituent Effects on ydration Equilibria nly when the carbonyl group is destabilized alkyl groups stabilize = electron-withdrawing groups destabilize = 2 = 3 : K = = F 3 : K = 22,000 Mechanism of ydration (base) Mechanism of ydration (base) Step 1: Step 2: Mechanism of ydration (acid) Mechanism of ydration (acid) Step 1: Step 2:

8 Mechanism of ydration (acid) Step 3: Which one of the compounds below has the fastest hydration rate? A) B) ) D) yanohydrin Formation yanohydrin Formation N N yanohydrin Formation yanohydrin Formation N N N

9 Example Example l l NaN, water then 2 S 4 l l N 2,4-Dichlorobenzaldehyde cyanohydrin (100%) 3 3 NaN, water then 2 S N (77-78%) Acetone cyanohydrin is used in the synthesis of methacrylonitrile Some reactions of aldehydes and ketones progress beyond the nucleophilic addition stage Acetal Formation Acetal formation Imine formation Enamine formation ompounds related to imines The Wittig reaction ecall ydration of Aldehydes and Ketones ' '

10 Alcohols Under Analogous eaction with Aldehydes and Ketones ' " emiacetal reacts further in acid to yield an acetal " ', Product is called an acetal. " ' Product is called a hemiacetal. " ' Product is called a hemiacetal. Example The structure shown at the right would be best classified as a(n) A) acetal. B) hemiacetal. ) hydrate. D) cyanohydrin ( 2 3 ) 2 l 2 Benzaldehyde diethyl acetal (66%) Diols Form yclic Acetals In general: 3 ( 2 ) benzene p-toluenesulfonic acid Position of equilibrium is usually unfavorable for acetal formation from ketones. Important exception: yclic acetals can be prepared from ketones. (81%) ( 2 ) 5 3 2

11 (78%) Example benzene p-toluenesulfonic acid 2 What is the product of the reaction between benzaldehyde and 1,3- propanediol? A) B) ) D) ydrolysis of Acetals " ' 2 " mechanism: ' 2" Acetals as Protecting Groups reverse of acetal formation; hemiacetal is intermediate application: aldehydes and ketones can be "protected" as acetals. Example The conversion shown cannot be carried out directly... because the carbonyl group and the carbanion are incompatible functional groups NaN I :

Strategy 1) protect = 2) alkylate 3) restore = Example: Protect 3 2 2 2 2 2 benzene p-toluenesulfonic acid 2 3 2 2 Example: Alkylate Example: Deprotect 2 2 2 2 3 2 2 3 3 2 2 3 2 l 1. NaN 2 2.

12 Strategy 1) protect = 2) alkylate 3) restore = Example: Protect benzene p-toluenesulfonic acid Example: Alkylate Example: Deprotect l 1. NaN I (96%) 3 What reagent and/or reaction conditions would you choose to bring about the following conversion? A) 1. LiAl 4 ; 2. 2 B) 2, 2 S 4, heat ) 2, Na, heat D) P, 2 l 2

pk a Values for Selected Compounds

pk a Values for Selected Compounds Appendix A pk a Values for Selected ompounds ompound pk a ompound pk a I 10 Br 9 2 S 4 9 + 3 3 7.3 3 S 3 7 Br 4.0 4.2 3 4.3 2 N l 7 [( 3 ) 2 ] + 3.8 [ 3 2 ] + 2.5 3 + 1.7 3 S 3 1.2 + 3 N2 0.0 F 3 0.2 l