Introductory Organic and Biochemistry

Quiz: Lipids.

Ouellette 2/e Ch 13.

Answer key
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This is probably a fairly challenging quiz, which will stretch you -- and thus can be good practice for you. You should be able to do #1-3 "closed book". If you need to look something up, go ahead. After all, this is a practice quiz. But use that as a reminder that you didn't quite know something that you probably should know. For #4, you will need a table of the common biological fatty acids. For #5, there is a separate note below; it is likely that you will need to look some things up.

1. Consider propanoic acid and hexadecanoic (palmitic) acid. One of these compounds is a lipid (or might reasonably behave like a lipid), the other is not. Which is which? Why?

2. Lipoproteins are proteins with lipids attached. We discuss proteins in Ch 15, but the only thing you need to know here is that the density of pure protein is about 1.3 g/mL. Compared to proteins, would you expect lipoproteins to be (more dense OR less dense OR about same density)? Choose correct term from the parentheses, and explain the logic of your prediction. (Note. The question is about the logic of the density of lipoproteins, not any specific knowledge you may have about it. If you know something about the density of lipoproteins, that may guide you to understand why, but that knowledge is not an explanation of why it is true.)

3. In each part, write a balanced equation to show how you could make the insoluble salt requested, by a simple double replacement reaction. Show phases. (Recall that most salts of the alkali metal cations are soluble, and all nitrates are soluble.)

a. barium sulfide

b. zinc undecylenate (Undecylenate is the carboxylate ion from an unsaturated C11 carboxylic acid. You can just refer to the ion as Und-. The zinc ion is Zn2+.)

4. Consider the fatty acid derivative (Z)-12-hydroxy-9-octadecenoic acid. It is an interesting natural product, and a derivative of it has an interesting application. These roles will be noted in the answer key.

a. Draw the structure of this compound.

b. What aspect of the structure is unclear from the name as given?

c. In the name, the Z could be replaced by _____ ?

d. Is your answer to part c based on "a rule", or on examining the specific structure? Explain.

e. The name given for this chemical (at the start of this question) is a good IUPAC name. If you wanted to name it as a simple derivative of a standard fatty acid, what would that name be?

f. The chemical is now treated by mild hydrogenation. What is the product? Give both the IUPAC name and a common name based on a standard fatty acid.

g. Following from the reaction in part f... The compound we want to make is actually the lithium salt of the acid. Show how you would make this, from the acid made in part f.

h. Consider the original compound given at the start of the question and the standard (common biological) fatty acid it is most closely related to.
* What is the difference between them, in terms of chemical structure?
* How would that difference affect the suitability of the two compounds for use in common bio membranes? Explain.

5. The following question is fairly "advanced". That is not because it is particularly difficult, but more because it uses considerable material that we did not emphasize. Feel free to do this question "open book". The question has an interesting "relevance", which will be discussed on the answer page.

Consider cholesterol. The four rings are commonly designated A-D, from lower left to upper right.

a. If we are going to discuss chemical reactions of cholesterol, we can make it easier to draw the reactions if we consider only two of the rings. Which two? Why?

b. What is the product of oxidation of cholesterol by ozone? (As suggested in part a, it is ok here to just draw the relevant parts of the molecule, based on the two rings.) What new functional group(s) is/are created here?

c. What other oxidizing agent would have given the same product(s)?

d. The product made in part b now undergoes an intramolecular aldol condensation.

   * Mark the positions of the acidic α (alpha) hydrogens, which make the aldol reaction possible? (That is, mark the α carbons that have acidic hydrogens.)

   * Draw the most likely aldol condensation product.

e. The product made in part b may also undergo an elimination reaction. What are the possible products?

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Last update: August 16, 2011