CHEMISTRY EXPERTS ONLY
Dr. Equinox
chem_exam.pdf
Name: _______________________________ (Ex2 rework)
CHM 3372, Winter 2016 Exam #2 Re-work Due Wed, 3/2/16
1. Make the ketone below from 13C-labeled formaldehyde and propane. Make certain to keep track of your labels throughout your synthesis. (27 points)
O
Name: _______________________________ (Ex2 rework)
2. (a) The reaction below can form two possible diastereomeric products. Draw the structures of both products, and the mechanism of the formation of either one. (4 points)
O 1. LiAlH4 2. NH4Cl, H2O
(b) What characterizes a thermodynamic product of a reaction (any reaction)? What characterizes a kinetic product of reaction? (2 points) (c) Which product from part (a) would you expect to be the thermodynamic product? Why? (2 points) (d) Which product would you expect to be the kinetic product? Why? (Note that this is not necessarily the "non-thermodynamic" product.) (2 points) (e) When this reaction is performed, regardless of what the temperature is, only one of the two possible products is ever formed. Which one? (1 points) (f) Why is the other diastereomer never formed? What must occur in order for it to be formed, which will never occur with this particular reagent? Why? (3 points) (g) Although the other diastereomer is never formed directly in this reaction, gentle heating with aqueous acid will isomerize the initial product into the other diastereomer. Draw the mechanism of the isomerization, and comment on why this isomerization occurs -- why one diastereomer will react completely to form the other. (5 points)
Name: _______________________________ (Ex2 rework)
3. This page seems like it was tough on Q#3. Let’s see if you do better the second time around. From the three alcohols shown, provide syntheses for the molecules below. For any SN2 or E2 reactions, use only non-halogen leaving groups – use a different leaving group which was covered in Ch. 11. (12 points) From: Make:
OH
OH
CH3 OH
O
O CH3
O
O
O
Name: _______________________________ (Ex2 rework)
4. (a) Once again, write the oxidation state of the metal (each complex is neutral, Nickel is Group 10; OTf is triflate, CF3SO3-), number of d electrons, and total valence electrons for the metal in each complex, and indicate what type of reaction is occurring. (8 points)
H Ni OTf
PPh3
Ni OTf
PPh3H
Ni OTf
PPh3 Ni
OTf
PPh3
Ni OTf
PPh3
H
(b) What are the reactant(s) and product(s) of the reaction? (This time, they are not drawn for you.) (2 points) (c) If the ethylene molecule were deuterated completely (CD2=CD2), where would the deuterium atoms end up in the product? Draw the structure, showing the position(s) of the deuterium atoms. Assume the catalytic cycle has run several times already. (2 points)
Name: _______________________________ (Ex2 rework)
5. (a) I defined a conjugated system generally as a π bond with an adjacent pure p AO (one of many different types). But I then stressed in class another geometrical necessity for a system to benefit from conjugation. What was that necessity? (2 points) (b) Some of the molecules below are conjugated, some are not. Circle the molecules in which the two p-AO-containing features (π bonds and/or cations) are not conjugated. (5 points)
C C C H
H H H
+
C+
H
H H
C C
C+
H
H
H
H
H
+
(c) The amide drawn to the right is extremely rigid, and has essentially no conformational freedom. Although it is technically an amide, in most ways it is much more similar (structure, reactivity, spectroscopy) to a molecule containing both a ketone and a tertiary amine. Compare the geometry of the rigid amide above with acetamide (ethanamide), which is a typical amide. Re-draw the rigid amide above, showing the C=O π orbitals as well as the nitrogen lone pair AO. Show resonance structures, as appropriate. (4 points)
(d) Use your geometrical comparison to make predictions and provide explanations for: (10 pts)
• Relative bond lengths (C-N, C=O)
• C=O IR stretching frequency
• 13C-NMR carbonyl chemical shift
• Relative basicity of the nitrogen lone pair
• Relative stability of the molecule
H3C N
O
H
Hacetamide
N O
Name: _______________________________ (Ex2 rework)
6. (a) This question concerns the MOs of methoxyethylene (or methyl vinyl ether, “MVE” CH2=CH-O-CH3). Draw an orbital interaction energy diagram, with the π MOs of ethylene on the left, the single pure p oxygen AO for –OCH3 on the right, and the resulting delocalized π MOs for MVE in the middle. For simplicity, assume the oxygen p AO is the same energy as the ethylene π bonding MO. (5 points) (b) Why is the second lone pair on oxygen left out of this MO diagram? (2 points) (c) Which ethylene π MO does the oxygen p AO have a larger interaction with? Why? Is this interaction stabilizing or destabilizing? Why? (4 points) (d) Is the interaction with the other ethylene π MO zero in magnitude? If so, why? If not, how does it affect the energies of the delocalized π MOs for MVE? (2 points) (e) Are the electrons in the delocalized π MOs for MVE (in the middle) more stable or less stable than those in a non-interacting π bond and O lp (on the sides)? Why? (2 points) (f) What is your prediction for the λmax of MVE, compared to ethylene (171 nm)? Why? (2 points)
