01/25/2006 10:02 PMPS-1
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Comprehensive Organic Chemistry - Chem 225b
Problem Set 2
Chapters 2 & 3
Due: Monday, January 30, 2006
The Conformation Module in the Study Aids will give you a good overview of the
subject of conformation. Work your way through ethane, propane, and butane.
The alkane module in ORGO will be of assistance in solving some of these
problems.
The Heats of Reaction module (StudyAids/thermochemistry) will of assistance.
1. Redraw (line angle formula) and name (IUPAC) the hydrocarbon in this
problem. For a dynamic view click here. For a static view click here.
2. Calculate the energy of the three staggered and three eclipsed conformations of
2,3-dimethylbutane about the C2-C3 bond.
3. The free radical chain chlorination of 2-methylbutane leads to four monochloro
constitutional (structural) isomers. Using the values for the relative reactivity of
primary (methyl), secondary (methylene) and tertiary (methine) hydrogens ---
1:4:5, respectively ---, calculate the expected percentage of each isomer. Draw
their structures and name them.
4. Consider the free radical bromination of neopentane (2,2-dimethylpropane).
a) Illustrate the initiation and propagation steps.
b) Provide the enthalpies of the propagation steps and the heat of the overall
reaction. BDEs are here.
c) Why was the enthalpy of the initiation step ignored?
d) Draw a reaction coordinate diagram (energy vs. reaction coordinate) for this
process. Label the enthalpies and activation energies. Which of the two activation
