Chem 3580-Prelim 1-S10 -Key

Chem 3580-Prelim 1-S10 -Key - Name(Last(First(Middle...

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Name: (Last) (First) (Middle Initial) 1 Circle Lecture time – 9:05 or 10:10 Organic Chemistry for the Life Sciences Chemistry 3580 Spring Semester 2010 Prelim 1 Thursday, February 18, 2010 7:30-9:00 PM Do not open until the proctor tells you to do so. There are 10 total pages. Please, count your pages before beginning the exam . Please, write your name at the top of each page in the spaces provided. Write all answers on the printed side of the exam in the locations indicated. 1. (10) 2. (10) 3. (12) 4. (20) 5. (14) 6. (16) 7. (18) Total (100)
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Name: (Last) (First) (Middle Initial) 2 1. (10 Points) Determine which of the following structures are aromatic, antiaromatic or non- aromatic? Be sure to show briefly how you arrive at your answers. (a) (d) (c) (b) S N N H H O N H (e) Reasoning Conclusion 16 ! electrons => antiaromatic N becomes sp 3 => no p orbital => Central ring nonaromatic. Benzene ring with nonaromatic substituent is still aromatic. Aromatic 12 ! electrons Constrained to be planar => antiaromatic Antiaromatic 14 ! electrons Constrained to be planar => aromatic Aromatic 14 ! electrons => aromatic Aromatic 16 ! electrons If constrained to be planar will be antiaromatic. So O & N can assume sp 3 . No p for overlap. Nonplanar Non-aromatic
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Name: (Last) (First) (Middle Initial) 3 2. (10 Points) (a) In a reaction with acid, 4-pyrone is protonated on the carbonyl oxygen to give a stable cationic product. Using resonance structures and the Hückel rule explain the stability of the protonated product. Be sure to indicate which resonance hybrid will be the most significant contributor and state why. O O H + O O H O O H O O H O O H O O H O O H 6 ! electrons aromatic => very stable => most significant contributor (b) Circle the least reactive under typical electrophilic aromatic substitution conditions.
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