Chapter 5 Workshop

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

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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.

Molecule	CCH angle	bond length, Å	BDE, kJ/mol	BDE, kcal/mol	IR stretch, cm-1	pKa
Ethane	109.6	1.10	420	100	2850-2960	62
Ethylene	121.7	1.08	444	106	3020-3100	45
Acetylene	180	1.06	552	132	3300	26

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3. Draw an atomic orbital model for CH2=C=CH2 .Consider first the geometry at each carbon and select the appropriate hybridization. label the orbitals used and show all valence electrons. The geometry should be clear from your drawing. Draw a dash/wedge structure for it.

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4. 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

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5. The dehydration of 3,4-dimethyl-2-pentanol upon treatment with sulfuric acid gives as the major product 2,3-dimethyl-2-pentene. Write a complete mehanism. There are several other minor products - predict what they would be.