HW09Key - reactive than aldehydes The electron-donating...

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Graded Homework Problem #09 – Answer Key Deadline : 3:00 p.m., Monday, 3/3/08 LATE WORK WILL NOT BE ACCEPTED OR GRADED!!! This problem is worth a total of 20 raw points. In each part below, circle the structure of the strongest acid . The most acidic proton in each molecule has a box around it. For full credit, please provide a brief explanation of your answer in the space provided. (a) (b) (c) O H H O O H Ph Ph O O H H O H O O H O N CH 3 CH 3 O H O N(CH 3 ) 2 O O H O H O H O H 3 C O H Clearly, one of the carboxylic acids must be the strongest acid, due to resonance delocalization of the negative charge in the conjugate base. A methyl group is electron donating compared to hydrogen (alkyl groups are electron-donating due to hyperconjugation; this is why 3° carbocations are more stable than 1° carbocations, and why ketones are less
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Unformatted text preview: reactive than aldehydes!). The electron-donating methyl group destabilizes the conjugate base of the structure on the right. By process of elimination, the circled structure must correspond to the strongest acid. For each acid, the negative charge of the conjugate base is delocalized through resonance. The circled structure has the greatest resonance delocalization of this charge. The charge can be delocalized into the aromatic ring, as shown below: O O O O O O O O etc. .. The circled structure is the only one that has a substituent with an electron-withdrawing resonance effect. This electron-withdrawing group helps to stabilize the negative charge of the conjugate base. O O N(CH 3 ) 2 O O O N(CH 3 ) 2 O O O N(CH 3 ) 2 O etc. .....
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This note was uploaded on 04/30/2008 for the course PHY 317L taught by Professor Ritchie/lang during the Fall '08 term at University of Texas.

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