318-11 - Organic Lecture Series CH 318 N LECTURE 11 Textbook Assignment Chapter 16 Homework(for credit POW 5 posted Todays Topics

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Organic Lecture Series 1 CH 318 N LECTURE 11 Textbook Assignment: Chapter 16 Homework (for credit): POW 5 posted Today’s Topics: Aldehydes/Ketones-reactions Notice & Announcements: Exam 1: Pick up in WEL 2.212 Organic Lecture Series 2 Aldehydes Aldehydes And And Ketones Ketones
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Organic Lecture Series 3 A second common theme is reaction with a proton or other Lewis acid to form a resonance- stabilized cation-- – protonation increases the electron deficiency of the carbonyl carbon and makes it more reactive toward nucleophiles B - CO R R H-Nu H-B R R H - R R H C Nu O-H R R R R H H-B + fast + + + + slow Tetrahedral carbonyl addition compound + + + Reaction Themes Reaction Themes Organic Lecture Series – often the tetrahedral product of addition to a carbonyl is a new chiral center – if none of the starting materials is chiral and the reaction takes place in an achiral environment, then enantiomers will be formed as a racemic mixture - R R' O R O R + H 3 O + OH R R + A racemic mixture A new chiral center is created Approach from the bottom face the top face
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Organic Lecture Series 5 Addition of C Addition of C Nucleophiles Nucleophiles Addition of carbon nucleophiles is one of the most important types of nucleophilic additions to a C=O group – a new carbon carbon -carbon bond carbon bond is formed in the process – Focus on addition of these carbon nucleophiles: RMgX RLi - C RC C - N A Grignard re ag e nt An organolithium An alkyne anion Cyanide ion Organic Lecture Series 6 Grignard Reagents • Given the difference in electronegativity between carbon and magnesium (2.5 - 1.3), the C-Mg bond is polar covalent, with C δ - and Mg δ + – in its reactions, a Grignard reagent behaves as a carbanion Carbanion Carbanion : an anion in which carbon has an unshared pair of electrons and bears a negative charge – a carbanion is a good nucleophile and adds to the carbonyl group of aldehydes and ketones
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Organic Lecture Series 7 –addition of a Grignard reagent to formaldehyde followed by H 3 O + gives a 1° alcohol CH 3 2 -MgBr O H-C-H O - [MgBr] + 3 2 -CH 2 HCl H 2 O OH 3 2 -CH 2 Mg 2+ ether 1-Propanol (a 1° alcohol) Formaldehyde + + A magnesium alkoxide Grignard Reagents Organic Lecture Series 8 Grignard Reagents –addition to any other RCHO gives a 2° alcohol MgBr H O - + H 2 O + Acetaldehyde (an aldehyde) + 1-Cyclohexylethanol (a 2° alcohol; (racemic)
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Organic Lecture Series 9 Grignard Reagents –addition to a ketone gives a 3° alcohol Ph- MgBr O Ph O - [MgBr] + HCl H 2 O OH Mg 2+ + Acetone (a ketone) ether + A magnesium alkoxide 2-Phenyl-2-propanol (a 3° alcohol) Phenyl- magnesium bromide
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This note was uploaded on 10/10/2010 for the course CH 57689 taught by Professor Goddard during the Spring '10 term at University of Texas at Austin.

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318-11 - Organic Lecture Series CH 318 N LECTURE 11 Textbook Assignment Chapter 16 Homework(for credit POW 5 posted Todays Topics

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