CHEM 2222 Chapter 19 Notes
CHEM 2222 Chapter 19 Notes Chem 212 - Organic Chemistry II
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Chem 212 - Organic Chemistry II
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This 36 page Class Notes was uploaded by annafen on Sunday May 29, 2016. The Class Notes belongs to Chem 212 - Organic Chemistry II at Vanderbilt University taught by Dr. Alissa Hare in Spring 2016. Since its upload, it has received 7 views. For similar materials see Organic Chemistry II in Chemistry at Vanderbilt University.
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Date Created: 05/29/16
19.1 Nomenclature of Carboxylic Acid Derivatives Carboxylic Acid Derivatives • Nucleophilic acyl substitution 1 Nomenclature of Acid Chlorides • Replace the -ic acid ending of the IUPAC name of the corresponding carboxylic acid by –yl chloride • The suffix -carbonyl chloride is used for attachments to rings other than benzene 2 Nomenclature of Acid Anhydrides and Esters • When both acyl groups are the same, the word “acid” in the corresponding carboxylic acid is replaced by “anhydride.” • When the two acyl groups are different, their corresponding carboxylic acids are cited in alphabetical order. • The alkyl group and the acyl group of an ester are specified independently • Esters are named as alkyl alkanoates. 3 Nomenclature of Amides • When naming amides, replace the -ic acid or -oic acid of the corresponding carboxylic acid with -amide • Substituents are listed in alphabetical order. Substitution on nitrogen is indicated by the locant N- 4 Nomenclature of Nitriles • Substitutive names add the suffix -nitrile to the name of the parent hydrocarbon chain that includes the carbon of the cyano group • Nitriles may also be named by replacing the -ic acid or -oic acid ending of the corresponding carboxylic acid with –onitrile • The suffix -carbonitrile is used when a ⎯ CN group is attached to a ring. 5 19.2 Structure and Reactivity of Carboxylic Acid Derivatives Stabilization of the Carbonyl • Stabilization depends on resonance 6 Stabilization of the Carbonyl Acid chlorides Acid Anhydrides Esters 7 Stabilization of the Carbonyl Amides • Amides have restricted rotation around the C-N bond 8 19.3 Nucleophilic Acyl Substitution Mechanisms Acyl Substitution Mechanism 9 19.4 Nucleophilic Acyl Substitution in Acyl Chlorides Acyl Chlorides 1. Anhydride formation - Acid chlorides react with carboxylic acids to give acid anhydrides 2. Alcoholysis - Acid chlorides react with alcohols to give esters • 1º alcohols react faster than 2º alcohols, which react faster than 3º alcohols 10 Acyl Chlorides 3. Aminolysis - Reaction of acid chlorides with ammonia, 1º or 2º amines to afford amides 4. Hydrolysis - Acid chlorides react with water to afford carboxylic acids 11 19.5 Nucleophilic Acyl Substitution in Acid Anhydrides Acid Anhydrides • The nucleophile connects to one acyl group. The other acyl is the leaving group • Acid anhydrides are slightly less reactivethat acid chlorides 12 Acid Anhydrides 1. Alcoholysis - react with alcohols to give esters 2. Aminolysis - Reaction with ammonia, 1º or 2º amines to afford amides 3. Hydrolysis - react with water to afford carboxylic acids 13 19.7: Reactions of Esters Esters • Esters are less reactive toward nucleophilic acyl substitution than acid chlorides or acid anhydrides 1. Aminolysis - Esters react with ammonia, 1º and 2º amines to give amides 2. Hydrolysis - Esters can be hydrolyzed to carboxylic acids under basic conditions or acid-catalysis 14 Esters 3. Esters react with Grignard reagents to give tertiary alcohols and two equivalents of the Grignard reagent adds to the carbonyl carbon 4. Esters are reduced by LiAlH (but not NaBH ) to primary alcohols 4 4 15 Acid Catalyzed Ester Hydrolysis • Carried out in the presence of a generous excess of water and under acidic conditions • It is the reverse of Fischer Esterification 16 Mechanism of Acid Catalyzed Hydrolysis 17 19.9 Ester Hydrolysis in Base: Saponification Saponification • Saponification means soap making • Saponification of triglycerides in animal fats have yielded soaps • The reaction is base-promoted hydrolysis of esters • To isolate the free acid the carboxylate must be acidified 18 Ester Hydrolysis in Base • The reaction isn’t base-catalyzed but base-promoted because the base ends up protonated by the resultant carboxylic acid 19 Reaction of Esters with Amines • The amine must be secondary or primary because a tertiary amine doesn’t have a proton to lose and the amide would be positively charged 20 19.11 Reaction of Esters with Grignard and Organolithium Reagents Reaction of Esters with Grignard Reagents • Two equivalents of the nucleophile are added and an alcohol formed • First equivalent of Grignard reacts to form a ketone • Second equivalent of Grignard reacts with the ketone • Organolithium reagents react in the same way 21 Reaction of Esters with LAH - • The first equivalent of H reacts to yield an aldehyde • The aldehyde is then rapidly reduced to the primary alcohol 22 19.12 Amides Physical Properties of Amides • There is significant double bond character between the C and N so there is not free rotation around that bond • More polar than esters with dipole moment in the range of 3.8–4.4 D • Amides have both a hydrogen bond acceptor and donor and therefore form H bond networks 23 Acidity of Amides • Amides are weaker acids than carboxylic acids since N is less electronegative • But more acidic than ketones 24 Synthesis of Amides • Synthesized from acid chlorides, acid anhydrides, and esters 25 19.13 Hydrolysis of Amides Hydrolysis of Amides • Amides are fairly stable in water but hydrolyzed in the presence of strong acid or base 26 Hydrolysis of Amides • Reaction also occurs in base 27 19.15 Preparation of Nitriles Synthesis of Nitriles 28 19.16 Hydrolysis of Nitriles Hydrolysis of Nitriles • Nitriles are also hydrolyzed in aqueous acid or base and is an irreversible reaction • If base is used, need to add acid during workup to protonate the carboxylate 29 Hydrolysis of Nitriles 30 19.17 Addition of Grignard Reagents to Nitriles Grignard Reagents • Addition of Grignard reagents to nitriles gives imines which are hydrolyzed to ketones • One equivalent of Grignard is added because the imine salt isn’t electrophilic and non-reactive 31 19.18 Spectroscopic Analysis of Carboxylic Acid Derivatives IR Spectroscopy • Typical C=O stretching frequencies are from 1 -7000 cm -1 • Conjugation (C=C π-bond or an aromatic ring) moves the C=O absorption to lower energy (right) by ~15 cm-1 32 HNMR • Protons on the α-carbon (next to the C=O) of esters and amides have a typical chemical shift range ofδ • Proton on the carbon attached to the ester oxygen atom have a typical chemical shift range of δ • The chemical shift of an amide N-H proton is typically between 5-8 ppm. It is broad and often not observed. δ= 2.0 s, 3H δ= 1.2 δ 2.0 δ 1.1 t, J=7.2 Hz, 3H 3H, s 3H, t, J= 7.0 δ= 4.1 q, J=7.2 Hz, 2H δ 3.4 2H, q, J= 7.0 NH 33 CNMR • Useful for determining the presence and nature of carbonyl groups. • The typical chemical shift range for C=O carbon is δ • Aldehydes and ketones - • Carboxylic acids, esters and amides - 14.2 60.3 21.0 170.9 CDCl 3 21.0 14.8 34.4 170.4 CDCl3 34 Nitriles • IR (highly diagnostic)- have a sharp −1 C≡N absorption near 2250 cm for alkyl nitriles • 2230 cm −1 for aromatic and conjugated nitriles • The ni1rile function group is invisible in the H NMR. The effect of a nitrile on the chemical shift of the protons on the α-carbon is similar to that of a ketone • The chemical shift of the nitrile carbon in the 1C spectrum is in the range of δ= 119 ~115-130 (aromatic region) 35 C C h t r H r C 2O e , H O O O P 4 1 R M O S 2 H 3 0 C C B R C H N t r O+ O y l H 2 e 3 H d H e H D + t B O H H 3 L 2O H H H O O D E t O H t L 2 H
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