Problem Set 2
Chapter 3, Alkanes
Due: Monday, February 4, 2008
(This photograph is in
the hallway across from 110 SCL) In 1885, as an addendum to a paper on
acetylenic compounds, Baeyer proposed that cyclopentane
was the least
strained of the cycloalkanes.
While he accepted the idea that the carbon atoms in
cycloalkanes were tetrahedral, he treated the
cycloalkanes as though they were flat. He argued that
there is only one cyclohexane carboxylic acid, not two
(axial and equatorial) as was predicted by a chair
cyclohexane.
Reading and Enrichment
Assignments:
a. Work through How to Draw Cyclohexanes (PowerPoint)
b. The Conformation Module in the Study Aids will give you a good overview of the subject of conformation.
c. View The Evolution of Formulas and Structure in Organic Chemistry During the 19th Century (PowerPoint).
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. How to manipulate Jmol structures. [What if there are two different longest chains? Check here.]
2. Compound A (MW=142.19), a 1,4-disubstituted cyclohexane,
has the following composition: C, 67.57%; H, 9.92%. The difference in
conformational energy for the two chair conformations of A is
0.4 kcal/mol. Using the data in Table 3-6, page 113 (Energy
Differences Between ..... Cyclohexanes), determine the structure of
A. Illustrate and explain. What is the conformational energy
difference for the stereoisomer of A, ---namely A'.
Explain and illustrate. Show the chair comformations of A and
A' with the appropriate equilibrium arrows to illustrate the
major and minor conformations. Label each conformation with its
energy.
3. Predict the heat of formation of n-decane using the data present
here.
Explain.
4. Using the heats
of formation tables,
explain the difference in the heats of formation of cis- and
trans-1,4-dimethylcyclohexane. What are the heats of combustion of
these stereoisomers? Show work. Draw a diagram of the heats of
formation and combustion for these stereoisomers relative to the
standard state. Put your values on the chart.
5. Compare the reported molar heat of combustion of cyclopentane
reported in Table 3-5 with that calculated using the data (ΔHfo
of cyclopentane, CO2 and H2O) present in the
heats
of formation tables.
6. Draw Newman projections for the eclipsed and staggered
conformations of 2-methylbutane viewed along the
C2-C3 axis. Calculate the energy of each
conformation, both staggered and eclipsed.
7. Check out the structure of limonene on
Wikipedia (don't worry about the issue of (+)-limonene or
(R)-enantiomer.) While the 2-D structure is truthful, the 3-D
version contains only "truthiness".
What would be a better presentation? Your 2-D version of your 3-D
revision must be able to be superimposed on the original 2-D version
of limonene.
2.