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Introductory Organic and Biochemistry

Quiz: Distinguishing isomers.

Ouellette 2/e Ch 10.

Answer key
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The questions here are all about C₅H₁₀O. There are many isomers with this formula. (This quiz makes use of information from all your organic chemistry material, especially Ouellette 2/e Ch 4, 8, 9, 10. If you are using another book, these are the chapters on alkenes, alcohols, ethers and simple carbonyl compounds.)

These questions are all open-ended. There are many possible answers. I encourage you to turn in your efforts, and I will look at them.

It may be particularly helpful to do one or two parts of each #1 and #3, and turn those in for feedback. You can then do more.

Be sure to explain your answers; the explanation is really the whole point.

Notes:

• The term "unsaturated" here refers only to C=C bonds.
• Remember that hydrogenation tests for both C=C and C=O double bonds.
• Reaction: Sodium can be used to test for alcohols. The reaction is mentioned by Ouellette on p 218; it is very similar to the reaction with water, which (hopefully) you learned in Intro Chem:
  water: HOH (l) + Na (s) --> HO^-Na⁺ (aq) + 1/2 H₂ (g)
  alcohol: ROH (l) + Na (s) --> RO^-Na⁺ (alc) + 1/2 H₂ (g)
  (RO^-Na⁺ is a sodium alkoxide. For example, CH₃O^-Na⁺ is sodium methoxide.)
• Reaction: 2,4-dinitrophenylhydrazine (DNPH) is a test for carbonyl groups, of either aldehydes or ketones. Briefly, adding DNPH gives a colored precipitate (typically yellow) with aldehydes or ketones.
• Reaction: Potassium permanganate, KMnO₄, is an oxidizing agent; it tests for a number of groups that are fairly easily oxidized: C=C double bonds, primary and secondary alcohols, and aldehydes. Ouellette introduces the reaction of KMnO₄ with C=C double bonds (Section 4.7), and the reaction of acidic dichromate ion (often written as chromic acid) with alcohols and aldehydes (Section 8.7). Although there are distinctions between them, permanganate and dichromate behave similarly.
• You are not responsible for knowing the new reactions that are presented here. However, given that the reactions are described here, you should be able to use the information for this quiz.

1. In each part, draw one isomer with the requested structural feature(s).

a. a primary alcohol
b. a secondary alcohol, with no unsaturation
c. a tertiary alcohol
d. an ether
e. an aldehyde
f. a ketone

2. Compare your compounds in parts a, d, e, f, above. Which one of them would probably have the highest boiling point? Why?

You should be able to answer this question even if you do not have structures for all the relevant parts of #1. Why?

3. You now test a compound to see what it is. In each part, you are given some results. Draw and name a compound that fits the data. Explain what each test tells you. (The parts are independent; that is, each part deals with a different compound. More than one compound may fit the data.)

Some of the reactions are from the text. Some are introduced in the notes above.

a. Reacts with sodium, not with potassium permanganate.
b. Reacts with KMnO₄, but not with Na.
c. Reacts with H₂/Pt, and with sodium.
d. Reacts with H₂/Pt, not with chromic acid.
e. Does not react with any of the following: H₂/Pt, Na, DNPH. (After you find such a compound... What would you expect it to react with?)

This quiz is based on an article by Robert Perkins (Kwantlen College, Surrey, BC, Canada), "Which Organic Molecule Should I Pick", Journal of Chemical Education 72:124, Feb 95.

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Last update: September 4, 2019