lecture 15 given - Lecture 15 Chemistry 310N Organic...

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ecture 15 Lecture 15 Chemistry 310N rganic Chemistry II for Prehealth Professionals Organic Chemistry II for Prehealth Professionals Unique number: 53185 Tu,Th 12:30-2:00 pm, Welch 2.224 Professor: Jonathan Sessler, Ph.D. sessler@mail.utexas.edu EXAM II -- In Class March 31st, will cover through Section 19.7. Chapter 19 is hard; studying it a bit over spring break is recommended. Some problems from Chapter 16 (the hard ones) are worth looking at too. And, have a great break!
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Nucleophilic Acyl Subst. The most important reaction of the first four classes of compounds (acid halides, acid anhydrides, esters, nd amides) is nucleophilic acyl substitution and amides) is nucleophilic acyl substitution • The mechanism involves an addition-elimination equence and results in the substitution of one sequence and results in the substitution of one nucleophile for another
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Nucleophilic Acyl Substitution py with an anion as nucleophile O - •• O •• Y - R O •• X - C R X C X C R Y + X his is a very PORTANT eneral reaction Understanding the Y This is a very IMPORTANT general reaction. Understanding the mechanism allows one to explain and predict a large body of organic chemistry!
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Nucleophilic Nucleophilic Acyl Acyl Substitution Substitution with uncharged with uncharged nucleophile nucleophile •• O •• •• H O HY C R X O H X C R X Y C R Y Obtained via protonated carbonyl intermediate Avoid anions in acidic media. Avoid cations in basic media. Generally, zwitterions are to be avoided!
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haracteristic Reactions Characteristic Reactions – In the general reaction, we showed the leaving group as an anion to illustrate an important point about them: e weaker the base the better the leaving group the weaker the base, the better the leaving group. R 2 N - RO - O RCO - X - Increasing basicity Increasing leaving ability
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haracteristic Reactions Characteristic Reactions – Halide ion is the weakest base and the best leaving group; acid halides are the most reactive toward ucleophilic acyl substitution nucleophilic acyl substitution. – Amide ion is the strongest base and the poorest aving group; amides are the least reactive toward leaving group; amides are the least reactive toward nucleophilic acyl substitution.
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Reaction with H 2 O - Acid Chlorides – Low-molecular-weight acid chlorides react rapidly with ater water. – Higher molecular-weight acid chlorides are less oluble in water and react less readily soluble in water and react less readily. O O + + CH 3 CCl H 2 O 3 COH HCl Acetyl chloride
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eaction with H nhydrides Reaction with H 2 O - Anhydrides – Low-molecular-weight anhydrides react readily with water to give two molecules of carboxylic acid. – Higher-molecular-weight anhydrides also react with water, but less readily.
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lecture 15 given - Lecture 15 Chemistry 310N Organic...

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