Last Year's Exam #1

C3443x EXAM 1
Professor Horne
September 30, 1996
50 minutes

1. (5 pts. ea.) Provide IUPAC names for the following:

2. (6 pts. ea.) Modify the structures below to show multiple bonds, unshared pair of electrons (indicated by dots), and locations of formal charge. Draw only the major resonance form with complete octets.

3. (6 pts. ea.) In each of the following pairs of Kekulé structures indicate (by circling yes or no) whether or not they are resonance forms.

4. (5 pts. ea.) In each of the following sets, circle the molecule that is most basic.

d) (5 pts.) DBU is a strong base. Upon monoprotonation, which nitrogen (N1 or N2) will become protonated? Explain using structures and no more than 15 words.

5(a) (6 pts) Consider 2-methylbutane. Circle its corresponding conformational energy diagram?

(b) (6 pts) Draw and label the corresponding Newman projections for 2-methylbutane in the lowest and second lowest energy conformations while viewing down the 2,3 carbon-carbon bond.

(c) (8 pts) Assuming essentially all the molecules adopt the lowest and second lowest energy conformations, estimate the relative percentages of each conformer at 25 °C (R=1.98 cal deg-1mol-1). Use the following values:

CH3-CH3 eclipsed 2.5 kcal mol-1 CH3-CH3 gauche 0.9 kcal mol-1 CH3-H eclipsed 1.4 kcal mol-1 CH3-H gauche 0 kcal mol-1 H-H eclipsed 1.0 kcal mol-1

6(a) (4 pts.) Consider the two decalin isomers below. Label which is cis and which is trans.

(b) (5 pts.) Only one of the isomers can undergo chair-chair interconversion. Explain using structures and no more than 15 words.

(c) (5 pts.) Indicate the more stable isomer and estimate the magnitude (in kcal mol-1) of the relative stability of the more stable isomer over the less stable one. Assume an axial-axial interaction is 0.9 kcal mol-1.