Chemistry 3719, Fall 2003 Exam 1 Name:

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1 Chemistry 3719, Fall 2003 Exam 1 Name: This exam is worth 100 points out of a total of 600 points for Chemistry 3719/3719L. You have 50 minutes to complete the exam and you may use molecular models as needed. Good Luck. 1. (6 pts) For each of the following molecules circle the most acidic proton and give its approximate pk a. pk a ~ 10 N 2 pka ~ 5 pk a ~ 16 C 3 1

2 2. (10 pts) Give acceptable names for each of the following molecules. You may use either IUPAC or trivial names for substituents. a. 5-ethyl-2,4,7-trimethyldecane b. 2,6-dimethylcyclohexanol c. Cl 2-bromo-3-chloro-5-methylheptane d. bicyclo[4.1.0]heptane e. cis-1,3-dimethylcyclopentane 3. (5 pts) Draw all of the possible isomers of C 5 10 that contain a cycle. Include cis and trans isomers where appropriate. C 3 2

3 4. (10 pts) Draw one other resonance form for each of the following anions: a. 3 C C 2 3 C C 2 b. N N c. d. e. 5. (6 pts) Identify any atoms in the molecule that are sp 2 hybridized. C 3 C N All the red atoms are sp 2 hybridized 3

4 6. (12 pts) Models may help with answering the following questions. a. In the space below, draw a chair conformation for trans-1-t-butyl-3-methylcyclohexane, then do a ring flip and draw the second chair conformation. Trans-Chair 1 Trans-Chair 2 Which of the two conformations is more stable? Explain your answer. Trans-Chair 1 is more stable since the large t-butyl group is equatorial thus avoiding any destabilizing 1,3-diaxial interactions. b. In the space below, draw a chair conformation for cis-1-t-butyl-3-methylcyclohexane, then do a ring flip and draw the second conformation. Cis-Chair 1 Cis-Chair 2 Which of the two conformations is more stable? Explain your answer. Cis-Chair 1 is more stable since the large t-butyl group is equatorial thus avoiding any destabilizing 1,3-diaxial interactions. f all the four conformations above, which will be the most stable and which will be the least stable? Cis-Chair 1 is the most stable situation, Cis-Chair 2 is the least stable. 4

5 7. (15 pts) Give structures for each of the following organic molecules: a. 2-bromo-4-chloro-3-ethylheptane Cl b. cis-3-methylcyclohexanol c. (1-methylpropyl)cyclopentane d. trans-1-isopropyl-2-methylcyclopropane e. 3-ethyl-4-methyldecane 5

6 8. (12 pts) Complete each of the following acid-base reactions then indicate the approximate pk a of the acid on each side of the equation. Which side (left or right or neither) will be favored in each case? a. right side favored Na + NaN 2 + N 3 pk a ~ 10 pk a ~ 36 b. + Na right side favored Na + 2 pk a ~ 5 pk a ~ 16 c. right side favored N 2 + C 3 Li NLi + C 4 pk a ~ 36 pk a ~ 50 d. ~ equal + NaC 3 Na + C 3 pk a ~ 16 pk a ~ (10 pts) Using the /δ- notation show any dipoles that are present in the following molecules. δ- δ- F Li δ- none Nδ- 6

7 10. (9 pts) Draw structures for each of the situations below: a. A Newman projection for the most stable conformation of C 2 C 2 anti conformer b. A Newman projection for a gauche conformation of C 2 C 2 gauche conformer c. A wedge-dash picture for the more stable isomer of 1,2-dimethylcyclopropane trans isomer 11. (5 pts) Pentane has a boiling point of 36 o C whereas 2-methylbutane boils at 28 o C. Explain the different boiling points for these isomeric compounds. Alkanes are held together by (relatively) weak intermolecular van der Waal s forces, which increase the longer the alkyl chain gets. When a branch is introduced the main chains are not able to get as close to each other and so the attractive forces between molecules are diminished. This results in less energy (and thus a lower temperature) being required to break the intermolecular forces and convert the liquid to a gas i.e. boil. 7