Name:
First Last Name:
UTEID:
CH 310M/318M
Fall 2006 Dr. Brian M. Bocknack
Thursday, September 28, 2006 7:009:00 p.m.
Do not open this exam booklet until you are told to do so! This exam is closed book, meaning no books, notes, calculators, or molecular models are allowed. PLEASE WRITE YOUR UTEID AT THE TOP OF EACH PAGE!!! Exams written in pencil are not eligible for regrades. Answers written in pencil with ink overlay will not be graded. If you do use a pen, only blue or black ink is acceptable. Answers written in red ink will not be graded. Be prepared to show your valid UT ID card to a proctor when attendance is taken, and also when you turn in your exam. You may not leave the exam room for any reason until you turn in your exam. Once you turn in your exam and leave the exam room, you will not be allowed to return!!! Page 2 3 4 5 (15) (15) (30) (40) Page 6 7 8 9 (30) (30) (36) (24) Total (300) Page 10 11 12 (40) (20) (20)
Midterm Exam #1
Including this cover page, 2 blank pages (scratch paper), and the last page, which contains a periodic table, this exam contains 15 pages. Please feel free to tear off the scratch paper and the periodic table to use as you work through the exam.
DO ALL QUESTIONS!!!
BEST OF LUCK!!!
UTEID: 1. (Problem worth 30 points; each part worth 5 points) PLEASE READ THIS QUESTION VERY CAREFULLY!!! In each part below, choose the best answer. Write the letter that corresponds to your choice in the box. There should only be one letter in each box. In other words, each question has one choice that is "best." (a) Consider the two structures shown below. All lone pairs and nonzero formal charges are shown explicitly in each structure. Which choice best describes the relationship between these structures?
O H3C
A. B. C. D.
CH3 CH2 H2C N O
N
The structures are equivalent resonance structures The structures are nonequivalent resonance structures The structures represent constitutional isomers None of the above. There is no clear relationship between these structures.
(b) Consider the following condensed structural formula: (CH3)2CHCH2CH2C(CH3)3 Which line-angle structure correctly represents the structure of this molecule?
A
B
C
D
(c) Consider the line-angle structure shown below. Which choice gives the correct molecular formula of this compound?
O
N H
A B C D
C8H15NO C9H19NO C9H20NO C9H17NO
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Problem #1 continues on Page 3... 2
UTEID:
Please follow the instructions given at the top of Page 2!!!
In lecture, we constructed the molecular orbital energy diagram for O2. The bonding in other second period diatomic molecules can also be described using the same kind of MO diagram. You'll need to refer to the MO diagram given below to answer parts (d), (e), and (f). Note that this MO diagram has already been filled in with electrons!
Energy
2p 2p 2p 2p 2s 2s 1s 1s
(d) Which molecular formula listed below is consistent with this MO diagram?
A B C D
O2 N2 O2+ F2
(e) What is the bond order of a diatomic molecule that has this MO diagram?
A B C D
0 0.5 1.0 1.5
E 2.0 F 2.5 G 3.0
(f) There is only one unpaired electron in the molecule described by this MO diagram. Which choice below gives the shape of the molecular orbital that holds this unpaired electron?
A
B
C
D
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End Problem #1 3
UTEID: 2. (Problem worth 30 points; each part worth 10 points) PLEASE READ THIS QUESTION VERY CAREFULLY!!! In each part of this question, write a Lewis structure for the molecular formula given. Write your structure in the box provided. Be sure to show all lone pairs and any nonzero formal charges clearly in each of your structures! Please note that none of these molecules is a resonance hybrid, so you do not need to worry about writing resonance structures when answering this question. Be sure to answer the two questions that appear to the right of each box (circle your choice). (a) COBr2
Hybridization of carbon? Polar or nonpolar molecule?
sp
sp2
sp3
Polar molecule Nonpolar molecule
(b) CH3NO (the bonding connectivity is suggested by the condensed structural formula)
Geometrical arrangement of e groups around C?
Linear Trigonal planar Tetrahedral
Geometrical arrangement of e groups around N?
Linear
(c) NO2 (the overall charge on this molecule = +1)
+
Trigonal planar
Tetrahedral
Hybridization of nitrogen? Polar or nonpolar molecule?
sp
sp2
sp3
Polar molecule Nonpolar molecule
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End Problem #2
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UTEID: 3. (Problem worth 40 points) PLEASE READ THIS QUESTION VERY CAREFULLY!!! In each part below, draw the indicated number of resonance structures in the large boxes provided. Be sure to show all lone pairs and nonzero formal charges! (Note: If you think there are more than the indicated number of resonance structures, it is probably because you are writing structures that are relatively unimportant. The structures you draw in the boxes should be those of relatively greatest importance.) After you draw your structures, indicate which structure is the most important contributor to the "true" structure of the resonance hybrid by placing the symbol "X" in the small box beneath it. If you think all of the structures are equally important, mark the box labeled "All structures are equivalent" with the symbol "X". If your answers are correct, you will either find that all structures are equivalent, or there will be one that is clearly more important than the others!!! (a) (12 points) Draw 2 additional resonance structures.
H C H N N
All structures are equivalent
(b) (16 points) Draw 3 resonance structures for the following polyatomic anion:
NO3
All structures are equivalent
(c) (12 points) Draw 2 additional resonance structures.
H H C C C O H
H2C
C H2
CH2
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All structures are equivalent
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UTEID: 4. (Problem worth 30 points; each part worth 10 points) PLEASE READ THIS QUESTION VERY CAREFULLY!!! In each part below, a condensed structural formula for a molecule that contains one or more multiple bonds is given. First, use valence bond theory to describe which orbitals overlap to form the bonds marked with the arrows. Write your answers in the boxes associated with the arrows. If the arrow points to a multiple bond, you only need to describe the bond ( bond or bond) indicated. Then, convert the condensed structural formula into a 3-dimensional representation of the molecule. Every bond needs to be explicitly shown in your 3-dimensional representation, using normal lines, wedges, and dashed wedges as necessary. It is not necessary to show lone pairs, however. Write your 3-dimensional representation in the large box on the right side of the page. An example is given to show you how to go about answering this question. Example:
H3C CH3
H H H C C
H
H H
sp3-sp3
3D representation
(a)
Cl3C
C
C
Cl
describe the bond
(b)
3D representation
describe the bonds
CH3CH
CHC
CH
describe the representation
describe bond
(c)
3D the bond
O H3C
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C
C H2
O
H
3D representation
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UTEID: 5. (Problem worth 30 points; each box worth 5 points) PLEASE READ THIS QUESTION VERY CAREFULLY!!! Ecteinascidine-743 (ET-743) is a compound that has been isolated from tunicates that live in clusters in the Caribbean and Mediterranean seas. Tunicates are sea creatures encased by tough membranes that are reminiscent of tunics. ET-743 is of interest because it has been shown to have remarkable anti-tumor activity. Specifically, it is hoped that ET-743 may soon play a prominent role in the treatment of certain soft tissue sarcomas and other cancers. The structure of ET-743 is shown below (line-angle structure). Various functional groups have been circled in this structure. Write the name of each functional group in the box pointing to it. Choose from the list of functional groups given below:
alkene alkyne aromatic ring alcohol ether thiol thioether alkyl halide
aldehyde ketone carboxylic acid ester amide amine acid anhydride nitrile
H3C H3CO HO CH3 N N S O O CH3 CH3 O H3CO OH H OH O O
O
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UTEID: 6. (Problem worth 36 points) PLEASE READ THIS QUESTION VERY CAREFULLY!!! There are a total of seven (7) constitutional isomers that have the molecular formula C4H10O. (a) Three (3) of these isomers are ethers. Draw all 3 of these ethers in the boxes provided, using any valid convention we have discussed for drawing organic structures. You'll receive 4 points for each unique, correct ether structure, 0 points for an incorrect structure, or for a structure that is not an ether, and 2 points for any repeated structure.
(b) Four (4) of these isomers are alcohols. Draw all 4 of these alcohols in the large boxes provided, using any valid convention we have discussed for drawing organic structures. You'll receive 4 points for each unique, correct alcohol structure, 0 points for an incorrect structure, or for a structure that is not an alcohol, and 2 points for any repeated structure.
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(c) In the small box that appears next to each large box in part (b), classify each alcohol as primary (1 secondary (2 or tertiary (3 Each correct classification is worth 2 points. ), ) ).
8
UTEID: 7. (Problem worth 24 points; each part worth 12 points) PLEASE READ THIS QUESTION VERY CAREFULLY!!! (a) There is one 3 amine that has the molecular formula C4H11N. Draw a structure of this amine in the large box below. You may use any valid convention we have discussed for drawing organic structures. Be sure to answer the 3 questions listed to the right of the large box. Write your answers to these questions in the small boxes.
Total number of lone pairs in this molecule? Total number of methylene groups in this molecule? Total number of 3 carbon atoms in this molecule?
(b) There is one ketone that has the molecular formula C4H8O. Draw a structure of this ketone in the large box below. You may use any valid convention we have discussed for drawing organic structures. Be sure to answer the 3 questions listed to the right of the large box. Write your answers to these questions in the small boxes.
Total number of lone pairs in this molecule? Total number of methyl groups in this molecule? Total number of sp2 hybridized atoms in this molecule?
9
UTEID: 8. (Problem worth 40 points) PLEASE READ THIS QUESTION VERY CAREFULLY!!! (a) (5 pts each) Draw a line-angle structure for each name given below. Write your answer in the appropriate box. 2,3,4,5-Tetramethylhexane 5-sec-Butyl-3-ethyl-8-methyldecane
(b) (5 pts each) Provide a name for each structure given below. appropriate box.
Write your answer in the
(c) (Each box is worth 5 points) The names given below are incorrect. Use the incorrect name to draw a line-angle structure in the top, larger box. Then, give the correct name of the compound in the small box that appears below the large box. 3,7-Diisopropylnonane 2,3-Dimethyl-5-propylheptane
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UTEID: 9. (Problem worth 40 points) PLEASE READ THIS QUESTION VERY CAREFULLY!!! Consider the conformation of 2-methylbutane shown below. A tetrahedral representation has been used to draw this structure. The carbon atoms of the parent chain are numbered to help you keep track of them as you work through this problem.
H
4
H C
3 2
CH3
C CH3
1
H3C
H
(a) (This part worth 10 points) Draw a sawhorse projection of the conformation shown above, in the box below and on the left. View the molecule from the direction indicated by the arrow above. In other words, carbon 2 should be closer to the viewer than carbon 3 is. To help you get started, the C2C3 bond is already drawn for you. Then, in the box below and on the right, draw a Newman projection for this conformation. Again, view the molecule from the direction indicated above (C2 is the front carbon and C3 is the back carbon).
3
2
Sawhorse projection
Newman projection
(b) (This part worth 10 points) The conformation shown above is actually one of the two (equivalent) most stable conformations of 2-methylbutane. In the box below, draw a Newman projection for the least stable staggered conformation of 2-methylbutane. Keep C2 in front, with the groups attached arranged in exactly the positions as they are found in the Newman projection you drew in part (a). In other words, rotate the groups on C3 with respect to those on C2 until you arrive at the least stable staggered conformation. Use the data listed below to calculate the total strain energy associated with this conformation. HH eclipsing interaction = 1.0 kcal/mol HCH3 eclipsing interaction = 1.2 kcal/mol CH3CH3 eclipsing interaction = 2.4 kcal/mol CH3CH3 gauche interaction = 0.9 kcal/mol
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Total strain (in kcal/mol) =
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UTEID: (c) (This part worth 10 points) Now, draw a Newman projection for the most stable eclipsed conformation of 2-methylbutane. As before, keep C2 in front, with the groups attached arranged in exactly the positions as they are found in the Newman projection you drew in part (a). In other words, rotate the groups on C3 with respect to those on C2 until you arrive at the most stable eclipsed conformation. Use the data listed in part (b) to calculate the total strain energy associated with this conformation.
Total strain (in kcal/mol) =
(d) (This part worth 10 points) Next, convert the Newman projection you drew in part (c) into a sawhorse projection. Write your answer in the box below and on the left. Once again, to help you get started, the C2C3 bond is given. Finally, draw a tetrahedral representation of this conformation. Use normal lines, wedges, and dashed wedges as necessary to indicate the arrangement of groups in space. C2 should be on the right in your tetrahedral representation, while C3 is on the left. Once again, to help you get started, the C2C3 bond is already drawn.
3
C
2
3
2
C
Sawhorse projection
Tetrahedral representation
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End of Exam!!!
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