CHE 24, Fall 1998
September 30, 1998
1. Multiple choice (10 points)
Which of the following structures represents gauche butane?
Which of the following compounds can have cis-trans isomers?
What is the formal charge for the indicated atom in the following compound?
|(a) +2||(b) +1||(c) 0||(d) -1||(e) -2|
Which of the following is not a nucleophile?
|(a) -OH||(b) H2O||(c) BF3||(d) NH3|
The reaction depicted in this reaction energy diagram can best be described as
2. (a) A student synthesized benzoic acid and was instructed to purify it by recrystallization. He dissolved the benzoic acid in a minimum amount of boiling water, and then isolated it by boiling off the rest of the water. How will his technique influence his yield? (4 points)
(b) A student prepared cyclohexane (bp 80.7 oC), and then she separated it from the starting material (cyclohexene, bp 83 oC) via simple distillation. How will the choice of separation method influence the purity of the sample? (4 points)
(c) Sodium sulfate (Na2SO4) was used in the acid-base extraction experiment. How does this material help purify the components of the separated mixture? (2 points)
3. Looking down the C1-C2 bond, draw the Newman projections for each of the maximum and minimum energy conformers of 1-bromo-2-methylpropane. Draw a graph that clearly shows the relative energies levels of the conformers as a function of the this bond rotation. (You may assume that a methyl group is larger than a bromine.) Clearly label your graph so that I can tell which energy corresponds to which conformer. (20 points)
4. Draw both chair conformations for the following substituted cyclohexane. Label the axial and equatorial substituents on each structure. Which conformer is more stable? Explain briefly. (20 points)
5. Provide the appropriate IUPAC names or structures for the following compounds. (5 pts ea)
6. Propose a mechanism to account for the following reaction. Your mechanism should explain how BOTH products can form. Show the structure of each intermediate, using arrows to show the flow of electrons in each step. (20 points)