Chemistry Workshops
1. Three dicarboxylic acids, C2H2(CO2H)2, I, J, and K, are catalytically hydrogenated (react with H2 in the presence of a catalyst) to give dicarboxylic acids with formulas of C2H4(CO2H)2. Hydrogenation of both I and J gives the same dicarboxylic acid L. Compound K hydrogenates to form compound M. Give structures for compounds I-M. Explain your reasoning.
OBSERVATION / / DEDUCTION
2. Consider the data about C-H bonds in the following table. Discuss the variations in bond length, bond dissociation energy, IR stretching frequency and pKa in terms of the observed geometries and our ideas relating structure and bonding.
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| Ethane |
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| Ethylene |
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| Acetylene |
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3. Give the product for the following reaction and write a detailed stepwise description (mechanism) for the transformation. Identify each species in the mechanism as a Lewis acid or Lewis base and use curved arrows to show the movement of electron pairs. Construct a plot that describes the energy of the system as a function of the progress of the reaction (reaction energy diagram). On your diagram, clearly label the positions of the reactants, any intermediate(s), and the product. Also, specify the energy difference that corresponds to the delta G° for the overall reaction and the energy difference that corresponds to delta G* for each step. Explain (in words) what is happening as the system makes its way from reactants to products.
H2C=CH2 + HCl --> CH3CH2Cl
4. The reaction of HBr with 2-methyl-2-propanol can, in principle, proceed by either an SN1 or SN2 mechanism. Show complete mechanisms for each of these processes, using curved arrows to indicate the movement of electron pairs. Construct reaction energy diagrams that describe the energy of the system as a function of the progress of the reaction in each case. Indicate at what point in the mechanism the selection of a preferred mechanism occurs and how the reaction coordinate diagrams help to illustrate the preference.
Repeat this exercise with the reaction of HBr and methanol.
Materials adapted from:
Peer-Led Team Learning: Organic Chemistry, 1/e
Jack A. Kampmeier, University of Rochester
Pratibha Varma-Nelson, St. Xavier University
Donald Wedegaertner, University of the Pacific
Prentice-Hall, 2001, ISBN 0-13-028413-0
http://www.sci.ccny.cuny.edu/~chemwksp/OrganicChem.html