Introductory Organic and Biochemistry

Quiz: Alkanes and cycloalkanes.

Ouellette 2/e Ch 3.

Answer key
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Closed book.

When a question asks for an explanation, you will normally receive zero credit if you give an answer without an explanation. The point is to emphasize reasons. Answers result from reasons; answers alone are not interesting.

1. Draw the structure of 3,4-diethylheptane.

2. Draw the structure of 2-bromo-2,3,3-trichloro-4-ethyl-1-iodohexane.

3. Is cyclopropane an isomer of propane? Explain. (There is only one relevant consideration. Be clear, and specific.)

4. Draw the structure of cis-1,3-dimethylcyclopentane. (For practice, try to draw this structure two ways: one using "stereo bonds" (e.g., wedges), and one not using them. Be sure that key features are very clear.)

5. Which has the higher boiling point, pentane or hexane? Why?

6. Which C4H10 isomer (n-butane or methylpropane) has the higher boiling point? Why? (Are there any other compounds with the given molecular formula?)

7. a. Draw the structure of propane. Show all the atoms.

b. There are 8 hydrogen atoms in your structure in part a. You could replace each one of them (individually) by a chlorine atom. In each case, you get a chloropropane. However, you don't get 8 distinct compounds.
* How many distinct (mono) chloropropanes are there?
* Draw them, and name them.

The following parts reexamine the issues from part b, in a somewhat different way. Before doing this part, try to see that you have the basics from part b.

c. Consider replacing each one of those 8 H from the original compound, propane, with a Cl atom. In how many cases do you get 1-chloropropane?

d. Now take the structure of propane that you drew in part a. Mark all of the H that you referred to in part c. For example, you might mark these as Ha. (That is, use Ha to mark all the H which, when replaced with a Cl, give 1-chloropropane.)

e. Now, use Hb to mark all the H which, when replaced with Cl, give 2-chloropropane.

Parts c-e introduce the idea of "equivalent hydrogens". It is hard to explain in words, without reference to a specific example. The purpose here is for you to discover "equivalent hydrogens" by working through an example. Hydrogens are equivalent if they behave exactly the same way. In this case, you see that substituting equivalent H's gives the same compound.

Ouellette develops the idea of equivalent atoms in a structure in the Explorations with Molecular Models at the end of Ch 3.

8. Which would you expect to be more soluble in water: propane or any (mono)chloropropane? Explain.

9. What is the simplest compound that contains a quaternary C atom?

10. Draw the structure of diiodobutadiyne. Show all the atoms (including all the hydrogens). Give the molecular formula.

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Last update: August 15, 2011