CHEM 240: Survey of Organic Chemistry at North Dakota State University Midterm Exam 01 - Tue, 23 Sep 2014!! Name:! KEY!

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1 EM 240: Survey of rganic hemistry at North Dakota State University Midterm Exam 01 - Tue, 23 Sep 2014!! Name:! KEY! Please read through each question carefully and answer in the spaces provided. A good strategy is to go through the test and answer all the questions you can do easily. Then go back and tackle the more difficult problems. Please make sure your structures are drawn clearly and indicate any necessary stereochemistry with bold or dashed bonds. Finally, think about what you know. ommon sense and reason can often help you out. You may use the blank pages of your test for scratch paper. Problem 1 8 pts Problem 7 9 pts Problem 2 10 pts Problem 8 14 pts Problem 3 10 pts Problem 9 9 pts Problem 4 14 pts Problem 10 8 pts Problem 5 6 pts BNUS 5 pts Problem 6 12 pts TTAL 100 pts hem 240 Midterm Exam 01! page 1! fall 2014

2 1. Identify the relationship between the following pairs of molecules as Identical, onstitutional Isomers, cis/ trans Stereoisomers or onformers. (check the appropriate box) (8 pts). identical constitutional isomer cis/trans stereoisomers conformers a) b) c) d) onsider the following molecule. Answer the questions pertaining to this molecule s structure. (10 pts) ow many primary (1 ) carbons are present in the molecule? ow many tertiary (3 ) carbons are present in the molecule? ow many sp hybridized carbons are present in the molecule? ow many sp 2 hybridized carbons are present in the molecule? ow many sp 3 hybridized carbons are present in the molecule? hem 240 Midterm Exam 01! page 2! fall 2014

3 3. For the following ønsted acid/base equilibrium indicate which side of the equation the equilibrium will favor by circling the reactants (left side) or the products (right side). In the boxes below each molecule indicate its role in the reaction as the acid, conjugate acid, base and conjugate base. (10 pts) + + pka = 4.75 pka = 15.5 acid base conj. base conj. acid 4. Provide the correct IUPA name for each of the following molecules. (14 pts) a) ethylcyclohexane b) trans-pent-2-ene c) E-3-methylhept-3-ene d) 4-ethyl-2,3-dimethylhexane 5. A mechanism for electrophilc addition to an alkene is shown below. For each of these two steps, draw the curved arrows (on the species below) showing how the electrons move. In total there should be three arrows for this mechanism. (6 pts) + + step 1 step 2 draw arrows on these for the first step draw arrows on these for the second step hem 240 Midterm Exam 01! page 3! fall 2014

4 6. The chlorinated hydrocarbon with the molecular formula 49 has four possible contitutional isomers. In the boxes below draw the structures for these isomers. (12 pts) 7. For the following questions, select the one best answer (circle the correct answer). (9 pts) (i) The term steric strain refers to...? (a) atoms coming too close to each other (b) staggered conformations (c) electron repulsion between bonds (d) compression of bond angles (ii) Which of the following would be an example of a Lewis Acid? (a) BF3 (c) N3 (d) 2 (e) 4 (iii) Which of the following statements about secondary carbons would be false? (a) a secondary carbon is attached to two other carbons (b) a secondary carbon has three hydrogens attached to it hem 240 Midterm Exam 01! page 4! fall 2014

5 8. Draw the structure for the following molecules. Make sure to indicate any stereochemistry clearly. (14 pts) a) trans-1-chloro-3-ethylcyclobutane b) 6-ethyl-2,3,4-trimethyloctane c) Z-3-methylhept-3-ene d) 1-bromo-3-ethyl-2,3-dimethylpentane hem 240 Midterm Exam 01! page 5! fall 2014

6 9. A reaction energy diagram for a general two step reaction is shown below (A reacts to from B which goes on to form ). (9 pts total) (a) In the boxes on the energy diagram, write the correct molecular species (A, B or ) at that point in the reaction progress. (5 pts) (b) n the energy diagram, draw an arrow indicating the activation energy for the slowest step. (2 pts) (c) Indicate by drawing a circle around all transition states on the diagram. (2 pt) step 1 step 2 A B E B A G reaction progress 10. For each pair of molecules below, circle the one that is the most stable (lowest in energy). (8 pts) (a) (c) (b) (d) hem 240 Midterm Exam 01! page 6! fall 2014

7 BNUS: Describe how cis/trans stereoisomers are important for our ability to see. (5 pts) β-carotene from carrots metabolized vitamin A metabolized When trans-retinal absorbs a photon of light, it isomerizes one of the double bonds to the cis isomer. This changes the shape of the molecule, and that changes the shape of the rhodopsin protein that it is buried in. This sends a signal to the brain that the eye has been struck by a photon. This is critical for vision. hν trans-retinal cis-retinal hem 240 Midterm Exam 01! page 7! fall 2014