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CHEM210_Fall2008_E1_KEY[1]

CHEM210_Fall2008_E1_KEY[1] - Name Page 1 I(21 points A...

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Name _____________________ Page 1 A. Diazomethane (CH 2 N 2 ) is a common reagent used for the conversion of carboxylic acids to methyl esters. However, use of this reagent is typically limited to small-scale applications due to its toxicity and shock-sensitivity. Diazomethane can be represented with two resonance structures whose atoms all have closed shell configuration and formal charges of -1, 0, or +1. Resonance form A is drawn below. C N N H H A (a) Draw the other resonance form ( B ) of diazomethane that has all closed- shell atoms and formal charges of -1, 0, or +1 on all atoms. B (c) Which of these two resonance forms is the most significant contributor to the actual structure of the molecule? circle one: (b) What are the hybridizations of atoms 1 3 of diazomethane? 1 A B briefly state the reason: 2 3 C N N H H 1 2 3 hybridization atom 1 2 3 1 1 1 (d) Provide a three-dimensional orbital representation for A. Use lines, dashes, and wedges for sigma bonds and to indicate the directionality of localized non- bonding electron pairs. Delocalized non- bonding electron pairs located in p-orbitals can be placed in either lobe of the p- orbital, but must be shown. Draw overlapped p-orbitals for pi bonds. 6 (a) Using the curved-arrow convention, provide the arrows that describe the connectivity change(s) for the left-to-right decarboxylation reaction shown below. O O O H H Br B . Certain molecules are prone to lose carbon dioxide in transformations known as decarboxylation reactions. In some instances this reactivity can be useful in the synthesis of organic molecules, and decarboxylation reactions also play a key role in the generation of biologically relevant compounds such as the neurotransmitter dopamine. C O O O H + + + Br H (b) Under normal reaction conditions (i.e., an open flask at room temperature), decarboxylation reactions are not reversible (that is, the products do not recombine to give the starting materials, even though a stronger acid is formed as a product than the one in the starting material). Explain briefly why it is highly unlikely for the reaction to reverse. 4 2 I . (21 points) C N N H H no partial sp 2 sp sp Form B bears the formal negative charge on the most electronegative atom. no partial, no credit if incorrect answer circled –2 for each missing or extra arrow –2 for each incorrect arrow CO 2 is a gas at room temperature and would bubble out of solution. The loss of CO 2 from the reaction mixture would drive the equilibrium towards products (Le Chatlier's principle).
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