Chemistry 3351: Organic Chemistry Thursday: Sept. 7:00pm 9:00/1 st Exam. Name: (please print)

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1 Chemistry 3351: Organic Chemistry Thursday: Sept. 7:00pm 9:00/1 st Exam 1 Name: (please print) Page Possible Points Score TOTAL 109

2 2 1. (3 pts each) Clickers in action: a) 2,3Pentadiene, C 3 C=C=CC 3, is a chiral molecule and exists as a pair of enantiomers. It is unique because it does not contain a chiral carbon center. Predict the hybridization of each carbon going from left to right along the carbon chain. A) sp, sp 2, sp 2, sp 2, sp B) sp 2, sp, sp, sp, sp 2 C) sp 3, sp 2, sp 2, sp 2, sp 3 D) sp 3, sp, sp, sp, sp 3 E) sp 3, sp 2, sp, sp 2, sp 3 b) Using MO theory, predict the potential existence of e 2 and/or e 2. A) e 2 and e 2 may exist. B) e 2 and e 2 may not exist. C) e 2 may exist and e 2 may not exist. D) e 2 may not exist and e 2 may exist. c) ow many constitutional isomers are there with the molecular formula C 6 14? A) 4 B) 5 C) 6 D) 7

3 3 d) Predict the magnitude of K eq for the reaction: C 3 CO O 3 O + C 3 CO 2 A) K eq = 0 B) K eq = 1 C) K eq >> 1 D) K eq << 1 Acid pk a Value 3O 1.7 C 3COO 4.7 N O 15.7 C 4 60 e) Arrange the constitutional isomers of C 5 12 in order of increasing boiling points. A) C 3 (C 2 ) 3 C 3 < (C 3 ) 2 CC 2 C 3 < (C 3 ) 4 C B) (C 3 ) 2 CC 2 C 3 < C 3 (C 2 ) 3 C 3 < (C 3 ) 4 C C) (C 3 ) 4 C < C 3 (C 2 ) 3 C 3 < (C 3 ) 2 CC 2 C 3 D) (C 3 ) 4 C < (C 3 ) 2 CC 2 C 3 < C 3 (C 2 ) 3 C 3 f) Select the IUPAC name of the compound shown below. C 2 Br F C 3 (A) (E)3bromo1fluoro2methylpropene (B) (Z)3bromo1fluoro2methylpropene (C) (E)1bromo3fluoro2methylpropene (D) (Z)1bromo3fluoro2methylpropene

4 4 2. (8 pts) Write line structures for each of the following compounds. I have done cyclohexane as an example. a) 1ethyl2propylcyclopentane b) 1, 1, 4tribromocyclohexane c) 3chloro1,1dicyclopropylcycloheptane d) 1(3chloropropyl)4tertbutylcyclooctane

5 5 4. (10 pts) Consider the hypothetical twostep reaction. k 1 k 3 A B C k 2 k 4 a) Is the overall reaction (A C) exothermic or endothermic? b) Label the transition states. Which transition state is rate limiting? c) What is the correct order of magnitude of the rate constants. i) k1 > k2 > k3 > k4 ii) iii) iv) k2 > k3 > k1 > k4 k4 > k1 > k3 > k2 k3 > k2 > k4 > k1 d) Which is the thermodynamically most stable compound? e) Which is the thermodynamically least stable compound?

6 6 5. (10 pts) Using Newman projections, draw a potential energy diagram for rotation about the C 2 C 3 bond of 2methylbutane.

7 7 6. (4 pts) The compound benzene has only one type of carboncarbon bond, and this bond has a length intermediate between that of a single bond and a double bond. Draw a resonance structure of benzene, that with the following structures, account for the carboncarbon bond length. benzene

8 7. (9 pts) Use the curvedarrow notation to derive resonance structures that convey the following ideas. In each case, also draw a single hybrid structure using dashed lines and partial charges that conveys the same meaning as the resonance structures. 8 a) The outer oxygen of ozone,, have an equal amount of negative charge. b) All CO bonds in the carbonate ion are of equal length. O O C O carbonate ion c) The conjugate acid of formaldehyde,, has substantial positive charge on carbon.

9 8. (10 pts) Imagine a reaction that can replace one hydrogen atom of an alkane at random with a chlorine atom. 9 C C Cl a) If npentane were subjected to such a reaction, how many different compounds with the formula C511Cl would be obtained? Give their line structures. b) Provide the same analysis as in part (a) for the same reaction carried out on 2,2 dimethylbutane.

10 9. (10 pts) Calculate the standard free energy change for the dissociation of acetic acid (pka = 4.76) 10

11 10. (10 pts) 11 a) Give the product X expected when methylenecyclobutane undergoes acidcatalyzed hydration. b) The ratelimiting step is protonation of the double bond; use as the acid catalyst. Draw the structure of the reactive intermediate formed in the ratelimiting step. c) Draw the transition state for the ratelimiting step. d) What is the ratelimiting step for dehydration of X (the reverse of the reaction shown above)?

12 11. (10 pts) Consider two 2p orbitals, one on each of two different atoms, oriented side to side, as shown below. Imaging bringing these nuclei together so that overlap occurs as shown in the figure. This overlap results in a system of molecular orbitals. 12 a) Sketch the shape of the resulting bonding and antibonding molecular orbitals. b) Identify the node(s) in each. c) Construct an orbital interaction diagram for molecular orbital formation. d) When two electrons occupy the bonding molecular orbitals, is the resulting bond a σ bond? Explain.

13 12. (10 pts) Which of the following reactions should have the greatest change? Why? 13 ( 3 C) 3 C C(C 3 ) 3 ( 3 C) 3 C C(C 3 ) 3 3 C C 3 3 C C 3