Chapter 20 Notes Part 1 (9/30-10/2)
Chapter 20 Notes Part 1 (9/30-10/2) CHEM-C 342
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This 13 page Class Notes was uploaded by Delaney Crane on Saturday October 3, 2015. The Class Notes belongs to CHEM-C 342 at Indiana University taught by Van Nieuwenhze M in Fall 2015. Since its upload, it has received 41 views. For similar materials see ORGANIC CHEMISTRY LECTURES 2 in Chemistry at Indiana University.
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Date Created: 10/03/15
Chapter 20 O O R i H R i R Aldehyde Ketone Aldehydes and ketones are covered in this chapter The above drawings show the structure of each The R group is an alkyl group or sometimes an aromatic The ketone has two R groups that are not always the same but they can be the same Common aldehydes and ketones include 0 O i L H H Formaldehyde Acetone Benzaldehyde Cinnamaldehyde O O O O OMe H Me H Me HO Acetaldehyde Vanillin carvone O Acetophenone Benzophenone Nomenclature aldehydes Identify and name the parent Identify and name substituents Assign locant to each substituent Assemble substituents alphabetically 99 Ntquot 0 MR The parent is butane longest carbon chain contains 4 carbons To name an aldehyde drop the e from the end of the parent and add al This creates butanal Don t confuse this with naming alcohols with 01 So what about when the aldehyde is not terminal 0 H 1 6 4 2 5 3 Now the aldehyde must be in the longest chain The parent is hexane longest carbon chain containing aldehyde has 6 carbons Drop the e and add al hexanal The substituent is a propyl group and is on the second C This compound is therefore 2propylhexanal And if there is a cycloalkane It is a derivative of the parent cycloalkane This compound is cyclopentanecarbaldehyde Nomenclature ketones Same 4 step process except you must assign a locant to the carbonyl You still drop the e but instead of adding al add one 0 1234 The carbonyl group is on C2 always assign locants so that carbonyl has the lowest number so this compound is 2butanone Preparation of Aldehydes also referred to as RCHO 1 PCC converts alcohols to aldehydes First this is the structure of FCC Then this is the basic mechanism in depth mechanism not shown in class H PCC k gt ROH R o This can also be thought of as LG leaving group Base H H N CG gt K BaseH LG 0 R O 2 Ozonolysis H H H 1 03 2 2DMS or R O R R ZnHCl The following mechanism can be found in the Klein book in section 911 on page 445 It depicts how ozonolysis takes place O K B K lt35 O Ozonide Molozonide O Mild Reducing Agent gt 2 O dimethyl sulfideDMS 0 0 or ZIMHZO 3 HydroborationOxidation of a terminal alkyne H BR2 RZBH H202 H R H gt gt R NaOH R H 0 Vinyl Borane The following steps show how to get from the Vinyl borane to the aldehyde H202 H R R quoty R H 8R2 H BO H O B OOH R H R H R H Vinyl Borane l H20 H OH Tautomerize lt R H R H This tautomerization happens because the aldehyde ending product is much more stable than the alcohol second to last product It is essentially just the movement of a proton Note R H O R H iHk These compounds are electrophiles at central C Nuc 107 v O i O The ketone is drawn in a box to show that it is planar in this case The nucleophile then attacks at an angle of 107 The attacking electrons must go into an unoccupied orbital which is 11 These orbitals are slightly pushed back from each other resulting in the angle of 107 Nuc Nuc O gt Illnn Aldehydes react more rapidly because alkyl groups are considered electron donating compared to the H C is more electrophilic stabilized less by alkyl groups Steric hindrance also plays a role the alkyl groups raise the energy of the transition state causing a higher energy needed for the reaction to occur Ab 4 R R39 R Ketone Aldehyde Nucleophilic Additions Basic Conditions 0 H H 39 Nuc OH N u C N U C OH 0 P Nuc This protonated ketone is very reactive which is a must when you have a weak nucleophile For acidic and basic conditions it is the same product in both cases just different steps to get there Neutral Nucleophiles R OH R SH R NH2 H39 R39 39CN Oxygen Nucleophiles H20 R OH Under Neutral Conditions Ho OH O lw HA gtlt R R39 R R39 Hydrate Under neutral conditions a hydrate is formed 0 When both R groups are a methyl group like acetone the starting material is favored 999 of the time 0 When both R groups are an H like formaldehyde the product hydrate is favored 999 of the time Basic Conditions H OH O O OH OH J j R OH R OH R 39 R R39 This reaction is said to be catalytic in base because the OH is not used up in the reaction It is used in the first step and regenerated in the last step Acidic Conditions OH H H OH H H OH O H O 0 H3O R O H R 0H2 R R39 R 39 R v R39 This reaction is said to be catalytic in acid because the hydronium ion is used in the first step and regenerated in the last Acetals Acetals are commonly used as protecting groups in organic synthesis RO OR 0 H A 2ROH H20 Acetal H means reaction is catalytic in acid The catalytic acid usually used is H2804 but sometimes it is toluene sulfonic acid TSOH or pTSA 0 Me S OH O Hemiacetals Hemiacetals cannot be isolate very easily O OH m lt H m H A R JJVB OR H Hemiacetal They are so hard to isolate because the following process will take place To push the process ahead there has to be away to eliminate H20 To go back you must add H20 You must use an acid catalysis because ROH are weak nucleophiles Using a Protecting Group with LAH LAH lithium aluminum hydride will reduce both functional groups below so to get to desired product a protecting group must be used 0 o O OH O O O O O HO LAH 11 OM gt gt gt OH e OMe H O H 2
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