Chemistry 14D
1.
Winter 2015
Exam 1B
Page 1
(9) Clearly and precisely define each term using no more than twenty words in each case. An example is not a
definition. Carefully avoid false restrictions and false generalizations.
(a) Leaving group:
(b) Transition state:
(c) Protic solvent:
2.
(24) For each reaction below circle the most likely mechanism: SN2, SN1, or NR (no reaction). For the cases
where a reaction does occur, write the major product(s) in the boxes. If only one product is formed or if no
reaction occurs write X in the unused box(es). The leaving group is not an acceptable product for this question.
S N2
(a)
Cl
H
NaI
S N1
acetone
+
NR
S N2
(b)
H3C
OH
S N1
H
Ph
CH3(CH2)7OH
+
NR
S N2
(c)
CH3
NR
+
Ph
S N2
S N1
LiCl
CH3OH
NR
(d)
OSO2CF3
S N1
O
H3CO
S
C(CH3)3
NaI, KF
(equal amounts)
CH3CH2OH
+
O
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Chemistry 14D
3.
Winter 2015
Exam 1B
Page 2
(6) Write the letter(s) of the reaction(s) in question 2 that have the indicated property. Example answer: 2(a),
2(b).
The best nucleophile: ________ The best leaving group: ________ A moderately polar solvent: __________
4.
All R
5.
I
(2) The SN2 product formed when (S)-2-iodooctane reacts with
NaOCH3 in CH3OH (shown at the right) is (circle one):
Mostly R, some S
50% R and 50% S
H
NaOCH3
CH3OH
Mostly S, some R
All S
(8) In this question we will figure out the effect on the rate of the reaction in question 6 when CH3OH is
completely removed (i.e., the reaction is conducted in the gas phase, without any solvent), but first we must
know how CH3OH influences the rate.
(a) Circle one statement that best describes the amount of stabilization received by solvation with CH3OH:
Nucleophile > transition state
Nucleophile < transition state
About equal for both
(b) For the nucleophile and transition state, changing from CH3OH to gas phase causes (circle one):
An increase in stability
A decrease in stability
No significant change in stability
(c) Whose stability is most significantly altered by solvent removal? Circle one:
Nucleophile
Transition state
Both effected about equally
(d) Therefore switching from CH3OH to the gas phase (circle all that apply)...
Increases activation energy
6.
Decreases activation energy
Increases rate
Decreases rate
(7) Along with an SN2 product, the question 4 reaction produces one or more additional products. Write two of
these products in the boxes below. If more than one is formed write the major product in the corresponding box.
If only one is formed write it in the major product box, then write an X in the minor product box. The leaving
group is not an acceptable product for this question.
I
H
NaOCH3
Major product
CH3OH
+
Minor product
Page 2 score =
Chemistry 14D
7.
Winter 2015
Exam 1B
Page 3
(3) Consider the solvolysis of molecule A. Draw the most likely carbocation formed by ionization of molecule
A. Include curved arrows to show the formation of this carbocation. If the carbocation has resonance show only
the most significant resonance contributor.
Ph
I
Cl
H2O
Molecule A
8.
Most likely carbocation
(3) By adding, subtracting, or changing into another element no more than three atoms, redraw molecule A so
that its ionization is obviously faster.
Ph
I
Cl
Molecule A
9.
Revised molecule A
(4) Consider the ionization that did not occur in question 7. Complete two very different reasons why this
carbocation does not form by adding no more than ten words in each case.
Reason #1: This carbocation does not form because...
Reason #2: This carbocation does not form because...
10. (6) Write two reasonable solvolysis products formed from your carbocation in question 7. These products are
not carbocations or leaving groups.
Ph
I
Cl
H2O
+
11. (2) Complete this sentence by writing one word: The biological molecule that we met in lecture and that
delivers methyl groups via an SN2 reaction is called...
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Chemistry 14D
Winter 2015
Exam 1B
Page 4
12. (2) Draw in the box a molecule that can undergo an E1 reaction but cannot
undergo an SN2 reaction.
13. (8) Using your molecule of question 12 as a starting point, write an example of an E1 reaction. Include all of the
reactants, the solvent, the mechanism, and major reaction product. If your reaction can produce more than one
product, show only the major product.
Reaction coordinate
Reaction coordinate
Profile 1
Profile 2
Energy
Energy
Energy
Energy
Questions 14 and 15 refer to these energy profiles:
Reaction coordinate
Reaction coordinate
Profile 3
Profile 4
14. (2) Write in the blank the number of the one reaction profile that corresponds to the fastest reaction: _________
15. (2) Write in the number(s) of the reaction profile(s) that cannot correspond to an SN1 reaction: _____________
16. (6) Consider mechanism steps B and C, then complete each statement below by adding no more than ten words
in each case.
Step B:
Ph3C
Cl
CH3CH2OH
Step C:
(CH3)3C
I
CH3OH
(a) Step B might be faster than step C because...
(b) Step B might be slower than step C because...
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Chemistry 14D
17. (6) This reaction does not occur:
Winter 2015
H
N
I
acetone
Exam 1B
H
N
Page 5
I
Complete each statement by adding no more than ten words in each case. Make the reasons distinctly different.
Reason #1: This reaction does not occur because...
Reason #2: This reaction does not occur because...
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