wade_ch18 - Chapter 18 Aldehydes and Ketones O R Aldehyde R...

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Chapter 18 Aldehydes and Ketones Nomenclature, spectroscopy, and physical properties (bp’s, solubility): Learn on your own. YOU WILL SEE SPECTROSCOPY ON THE SECOND EXAM! Physical Properties : What should we know about the C=O (“carbonyl”) functional group when we see it? Consequence: We should know that the C=O is ________________ We therefore predict that ( 1 ) Certain naturally occurring aldehydes are fragrant ( 2 ) 18-1 Aldehyde R O Ketone R O Carboxylic acid R O R OR' O R N O R Cl O R 2 R 1 R 1 , R 2 R H C O vanillin H C OH O OCH 3 cinnamaldehyde carvone (+)-enantiomer = (-)-enantiomer = O O
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Syntheses of aldehydes and ketones : Old methods : Aldehydes via 1 o alcohols and Cr 6+ reagents Ketones via 2 o alcohols Wade, Sec. 11.2 Aldehydes/ketones via alkenes Ozonolysis, Wade, 8.15B Ketones (aromatic) via 2 o benzenes F/C Acylations, Wade, Sec. 17.11 Ketones via alkynes Markovnikov addition of Hg 2+ , H 2 SO 4 , Wade, Sec. 9.9F Aldehydes via alkynes anti-Markovnikov addition hydroboration/oxidation, Wade, 9.9F New methods : Aldehydes via dithianes “thia-” = ( 3 ) Ketones via dithianes Concept: A 1,3 dithiane is a _______________. It can be deprotonated by _______________ and then alkylated… Example : 18-2 n -BuLi S S 1,3-dithiane ( p K a ~ 32) H H 1) n -BuLi n -BuLi = n -butyllithium = CH 3 CH 2 CH 2 CH 2 Li = Hg 2+ , H , H 2 O Hg 2+ , H , H 2 O S S S S S S Label? Label? Label? Label? Label? CH 3 CH 2 CH 2 CH 2 Label? Label? Label? Label? Labels? R 1 X 2) R 2 X See: Think: Predict: See: Think: Predict:
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Ketones via Carboxylic Acids - similar to Grignard Reaction ( 4 ) Ketones via Nitriles Also similar to Grignard Reaction. Mechanism : 18-3 R O Why are 2 equivalents of the alkyllithium (R'-Li) needed? 1) 2 equiv. R'-Li 2) H 3 O workup O H 2) H 3 O workup R O O O Labels? Labels? See: Think: Predict: R N C 1) R'-MgX (or R'-Li) 2) H 3 O workup + NH 4 R R' C O Label? R N C H 3 O workup + NH 4 R R' C O R' MgX H 3 O workup R R' R R' Labels? See: Think: Predict: Labels?
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H Al O O O Li CH 3 CH 3 H 3 C CH 3 H 3 C CH 3 CH 3 CH 3 CH 3 l Aldehydes via acid chlorides Problem: Many carboxylic acids and derivatives can be reduced using LiAlH 4 , but the reaction goes all the way to the __________________! ( 5 ) Recall that LiAlH 4 is the reagent that transfers H: How can we stop at the ________________ stage? We would want… ( 6 ) to use a reagent has only one hydride (H: ) a reagent that is bulky to use low temperature The selective reducing agent “lithium tri– t –butoxy aluminum hydride” (LiAlH(O– t –Bu) 3 ) works quite well… Reaction ( See - Think - Predict ): 18-4 O C OR' R O C OH R O C Cl R carboxylic acid LiAlH 4 OH CH 2 R ester acid chloride (slow) LiAlH 4 (fast) Labels? See: A
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wade_ch18 - Chapter 18 Aldehydes and Ketones O R Aldehyde R...

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