CHEM 2222 Chapter 17 Notes
CHEM 2222 Chapter 17 Notes Chem 212 - Organic Chemistry II
Popular in Organic Chemistry II
Popular in Chemistry
Chem 212 - Organic Chemistry II
verified elite notetaker
This 37 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 6 views. For similar materials see Organic Chemistry II in Chemistry at Vanderbilt University.
Reviews for CHEM 2222 Chapter 17 Notes
Report this Material
What is Karma?
Karma is the currency of StudySoup.
You can buy or earn more Karma at anytime and redeem it for class notes, study guides, flashcards, and more!
Date Created: 05/29/16
17.1 Nomenclature Aldehyde Nomenclature • Longest chain that contains the aldehyde group is the parent chain • Aldehyde carbon is C-1 • When a formyl group (CH=O) is attached to a ring, the ring name is followed by the suffix -carbaldehyde. 1 Ketone Nomenclature • With ketones, the -e ending of an alkane is replaced by -one in the longest continuous chain containing the carbonyl group • The chain is numbered to give a lower number for the carbonyl group 2 Nomenclature • Ketones and aldehydes have preference over alcohols, halides, alkenes, and alkyl groups in name and numbering • Aldehydes have preference over ketones in name and numbering • Then the ketone is an oxo substituent 3 17.2 Structure and Bonding: The Carbonyl Group Structure and Bonding • The carbonyl is flat with sp hybridization of carbon and oxygen with bond angles about 120 o. • The C=O comprises a σ-bond and a π-bond (shown) similar to ethylene 4 Carbonyl and Polarity • Carbonyl groups have a significant dipole moment • This polarization makes the carbon electropositive and electrophilic 5 17.3 Physical Properties Physical Properties • Aldehydes and ketones have higher boiling points than alkanes and alkenes due to stronger dipole-dipole forces • Have lower boiling points than alcohols which have stronger hydrogen bonding • More water soluble than alkanes and alkenes since the carbonyl can hydrogen bond to water but less than alcohols 6 17.4 Sources of Aldehydes and Ketones Reactions that Form Ketones and Aldehydes 7 Reactions that Form Ketones and Aldehydes 8 17.5 Reactions of Aldehydes and Ketones Review of Reactions of Carbonyls 9 17.6 Principles of Nucleophilic Addition: Hydration Effects of Structure on Equilibrium • Water can reversibly add to the carbonyl carbon of aldehydes and ketones to give 1,1-diols (geminal or gem-diols) • The hydrate is in rapid equilibrium with the carbonyl 10 Effects of Structure on Equilibrium • Trifluoromethyl substituents are electron withdrawing and therefore destabilize the carbonyl • Opposite effect to alkyl substituents: hydrate favored! • Conversely, adding bulky substituents reduce the amount of hydrate present 11 Mechanism of Hydration in Basic Solution 12 Mechanism of Hydration in Acidic Solution 13 17.7 Cyanohydrin Formation Cyanohydrin Formation • Addition of hydrogen cyanide to an aldehyde or a ketone produces a cyanohydrin • Cyanohydrins contain a hydroxyl group and a cyano group bonded to the same carbon • Forms a new C-C bond 14 Mechanism of Cyanohydrin Formation 15 17.8 Reaction with Alcohols: Acetals and Ketals Formation of Hemiacetals and Acetals • Acetals and Ketals are similar to hydrates (geminal diols) but using an alcohol as the nucleophile rather than water • Acetals are formed from aldehydes • Ketals are formed from ketones 16 Mechanism of Acetal Formation • Removing water drives the reaction in the forward direction – use a Dean Stark Trap • Adding water moves the reaction in the backward direction 17 Cyclic Acetals • Cyclic acetals and ketals are synthesized from aldehydes or ketones and 1,2- or 1,3-diols 18 17.9 Acetals and Ketals as Protecting Groups Protecting Groups • Protecting group - converts a functional group that is reactive with a set of reaction conditions into a new functional group (with the protecting group) that is non-reactive with the reaction • The protecting group is • Acetals and ketals are used to “protect” aldehydes and ketones during reactions taking place in strongly basic conditions or in the presence of nucleophiles 19 Protecting Groups 20 17.10 Reaction with Primary Amines: Imines Formation of Imines • An imine is like a carbonyl group but with a C=N-R instead of C=O 21 Mechanism of Imine Formation 22 Reactions with Derivatives of Ammonia 23 17.11 Reaction with Secondary Amines: Enamines Formation of Enamines • Reaction with secondary amines yields enamines • The intermediate hemiaminal is dehydrated to form the enamine • Requires a hydrogen at the α-position of the ketone 24 Mechanism of Formation of Enamines 25 17.12 The Wittig Reaction Wittig Reactions • The synthesis of an alkene from the reaction of an aldehyde or ketone and a phosphorus ylide (Wittig reagent) • An ylide is a dipolar intermediate with formal opposite charges on adjacent atoms (overall charge neutral) 26 Mechanism of Formation of Wittig Reagents • The Wittig reaction is highly selective for ketones and aldehydes • Esters, lactones, nitriles and amides will not react but are tolerated in the substrate. • Acidic groups (alcohols, amine and carboxylic acids) are not tolerated • E/Z geometry is complex to determine and require specialized reagents 27 Reaction of an Ylide with a Ketone 28 17.13 Stereoselective Addition to Carbonyl Groups Stereoselective Addition to Ketones • Stereoselective reactions can occur under substrate-control • The substrate has a face of the planar carbonyl that is blocked by steric hindrance 29 17.14 Oxidation of Aldehydes Oxidation of Aldehydes • Aldehydes are oxidized by Cr(VI) reagents to carboxylic acids in aqueous acid • The reaction proceeds through an intermediate hydrate 30 Oxidation of Aldehydes • PCC and PDC selectively oxidize primary alcohols to aldehydes because the reaction is performed in anhydrous conditions • Without water, you have no hydrate intermediate 31 17.15 Spectroscopic Analysis of Aldehydes and Ketones Infrared Spectroscopy • Aldehydes and ketones have strong C=O stretching absorption in the range • Aldehydes have two weak C-H stretches near IR spectrum of butanal 32 Infrared Spectroscopy • Conjugation moves the C=O stretch to lower energy (right, lower cm ) -1 • Ring (angle) strain moves the C=O stretch to higher energy (left, higher cm -) 33 H NMR Spectroscopy • Aldehydes have a signal for the aldehyde proton at • Hydrogens on the carbon adjacent to a carbonyl appear in the range • Aldehyde Hs will couple with the α-hydrogens with J = 2Hz 34 13 C NMR Spectroscopy • Aldehyde and ketone carbonyl carbons appear at • Carboxylic acids and ester carbons are found 35 Mass Spectometry • Aldehydes have M-1 peak. • Loss of acylium gives a major fragment in both ketones and aldehydes 36
Are you sure you want to buy this material for
You're already Subscribed!
Looks like you've already subscribed to StudySoup, you won't need to purchase another subscription to get this material. To access this material simply click 'View Full Document'