Chem 255 Exam1 Answers

Chem 255 Exam1 Answers - Chemistry 255 Exam I Fall 2000 ALL...

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Unformatted text preview: Chemistry 255 Exam I Fall 2000 ALL ANSWERS MUST BE IN INK** Name Cr‘ (0 ID# Please read the following questions very carefully. 1. Provide tw_o (2) unique Lewis structures that have the molecular formula C2H3N (show all non- bonded electrons and provide formal charges where appropriate): (12 pts) (EC—Can: H9? 2 CIMH 2. Add unshared pairs of electrons as needed to complete the valence shell of each atom in the following molecule, and assign formal charges to all non-hydrogen atoms (put 0 if there is no charge): (14 pts) H H'O‘ @ I II "a H— C-—C O: | I 0 ~ H H 3. Draw an accurate 3—dimensiona1 depiction of the following molecule showing all bond angles, and indicate the hybridization for the atomic orbitals of all non-hydrogen atoms. (16 pts) CH3CO CECH '2' of? 4. Provide structures for the following molecules: (10 pts) a) 3—tert-butyl-6—methyloctane H 5. Provide IUPAC names for the following compounds: (10 pts) A if 3 6. Draw Newman projections for the lowest energy and highest energy conformations of ; methylpropane looking down the C1-C2 bond of the chain. With the following information, predict the difference in energy between the highest and lowest energy conformations (torsional strain resulting from eclipsed C-H bonds is 1.0 kcal/mol and that for eclipsed OH and C-C bonds is approximately 1.5 kcal/mol) (16 pts) H H 3 H CH3 1 . /\ i :H 1* \4 H CH3 u W3 lowest highest Energy difference: Lf KC‘k/W ( 7. Provide names for the three unique types of functional groups in the molecule below. (15 pts) a defensive toxin produced by the whirlgig beetle 8. Provide m constitutional isomers with the molecular formula CSHIO. (20 pts) -- -- 9. Draw the lowest energy chair conformation for trans—l-tert—butyl-3-methylcyclohexane showing all axial and equatorial hydrogens: (17 pts) 10. Arrange the following acids from strongest to weakest (A — C, acidic proton is circled), and provide a detailed rationale for your choice based on all of the following that apply: inductive effect, electronegativity, resonance, hybridized atomic orbitals, and bond dissociation energy. (20 pts) 0 O m A (9 $69 0 (pKa 19.3) 0 R l N H /\, H H C -H —— > __ > _.3___ A B Q strongest acid weakest acid Rationalize: Why A is a stronger acid that B: Extra credit problem: (5 pts) Is the indicated bond ionic, polar covalent or non-polar covalent? refilfl ...
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Chem 255 Exam1 Answers - Chemistry 255 Exam I Fall 2000 ALL...

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