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CHEMISTRY 204, Sp., 1990
Exam II: Cyclohexanes, Free-radical halogenation; Stereoisomerism; Nucleophilic Substitution
(SN2, SN1); Elimination (E-2, E-1); Add'n of H2 to Multiple-Bonds.
Partial credit will be given when/where appropriate. Brief answers are most welcome, citing specific
experimental support from text or below. Long, rambling answers are not necessary!
Note: There is no particular order to questions presented here. Answer first those questions you know
best. Partial credit will be given when/where appropriate. Brief answers are most welcome, citing
specific experimental support from text or below. Long, rambling answers are not necessary!
Useful Information:
pKa of Acids pKa's of Acids: at 25°: ΔG° = -2.303 RT log K = -1.366 log K (kcals/mole)
H2SO4 -12
CH3SO3-H <0
RNH3+ 10
HI -9
H3PO4 2.2
CH2(CN)2 11.2
HBr -8
HF 3.2
H2O 15.7
HCl -7
CH2(NO2)2 3.6
Alcohols 16-19
+
H3O -1.7
H2S 7.0
(CH3)CO 20
HCN 9.1
H-N+N <0
R-CCH 25
+
+
H-O R2 <0
NH4 9.2
CH3CN 25
+
H-S R2 <0
C6H5OH 9.9
NH3 to R2NH 35-36
alkanes RH 40-60
O
O
C
OH
CH3
4.8
O
C
CH3
O
C
CH2
CH3
O
C
11
CH3
O
CH3
25
Supplies: Common Solvents of all kinds: non-polar; hydroxylic; dipolar, aprotic
Inorganic Reagents, including SOCl2, CO2, Mg, Na, K, Li, Al, NaN3, PX3, CrO3, ZnCl2, D2O, AgBr, AgNO3, RCN,
NaSH, NaOH, NH3, H2SO4, HX (Cl, Br, I), NaSCN, NaH, KSCN, KCN, NaSH, NaOH, NH3, H2SO4, HX(Cl,Br,or I),
NH2OSO3H, I2, Ag2O, Zn(Ag), Zn(Cu), LiX (Cl, Br, I), NaI, NH2OH, NH2-NH2, Raney Ni, Hg+2, CrO3, KMnO4,
H2O2, OsO4, B2H6, ZnCl2, DMSO, HMPT, DMF, (C2H5)3N, CH3CH2NH2.
Non-cyclic Organics: one thru five carbon alcohols, H-CC-H, CH3CO2H, , CH3SO2Cl, CH2=O, (C2H5)3N,
(CH3)2SO4, "PCC", CH2=CH-CH2-OH, acids, aldehydes, amines, alkenes, alkynes, ketones, thiols (R-SH); HCC-H, CHCl3, CCl4, CH2=CH-CH2OH, CH2I2, (C2H5)3B, NO, HO-CH2CH2OH, HS-CH2CH2SH, (CH3)3SiCl, CHBr3,
CBr4 CF3CO3H (pertrifluoroacetic acid), CF3-SO2Cl (for "triflates"), CH2=CH-Br, CH2N2, CH2=C=O
Cyclic Organics: Cyclopropanol to Cycloheptanol, C6H5-SO2Cl, pyridine, p-CH3C6H4SO2Cl or
O
CH3
S
Cl
CH2
OH
O
(for "tosylate" prep.),
, CH2 CH2 ,Cyclopropanol to
Cycloheptanol, C6H5SO2Cl, pyridine, C6H5-CH2-OH, C6H5-NH-NH2, m-ClC6H4CO3H ( a per-acid), C6H5-CH2-Br,
C6H5-CO2H, C6H5-CH3, C6H5-C(O)-O-O-C(O)-C6H5 (a peroxide), m-ClC6H4CO3H ( a per-acid),PPh3
Bases (Strong); Reducing Agents: NaH, KH, LiN(-iPr)2 ("LDA"), LiAlH4, NaBH4, CH3Li, KN(SiMe3)2, C6H5-,
LiAlH(O-t-Bu)3
O
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Conformational Energies for Monosubstituted Cyclohexanes
Group: -ΔG° (axial – equatorial) Kcal mol-1 (25°C)
F 0.25
Cl 0.5
-CN 0.2
-CCH 0.4
-OH 0.5
-CH2CH3 1.8
-OCH3 0.7
CH(CH3)3 2.1
-OTos 0.5
-OC2H5 .0.9
C6H5 3.1
-SH 0.9
-CO2CH3 1.3
Br 0.5
I 0.45
-NH2 1.0
CH3 1.7
C(CH3)3 5-6
1.(09) You have been hired to complete the chemistry at a new plant in Edmonton, Alta., that
will make a new octane booster, methyl t-butyl ether (MTBE). OUTLINE an acceptable route to
prepare MTBE from available materials in a minimum # of steps consistent with high yield.
(Structure of MTBE "For Sale" for 3 pts.)
2
2.(a1) Aplysiapyranoid A, (I), a sea algae component, has recently been synthesized at Brown
University(ACS Meet, Boston, 4/90).
a) Given a chair-like ring (with -O- in place of a -CH2-) and all the axial and equatorial bonds
shown, complete that conformation with the substituent’s of (I) in their proper location and
orientation, then draw the second chair conformation that is in equilibrium with the first.
H
Br
Br
H
CH3
Cl
O
CH3
CH3
(I)
O
b) Using the list of "A" values provided, calculate the total destabilization energy for each of the
chairs above, then use these energies and
1. determine which chair is more stable:
Basis:
2. Calculate the approximate equilibrium constant, K = [rt. chair]/ [left chair]
3. Please show some work for the Destabilized Energies and for K.
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3.(20) Continue with (I).
a) For each tetrahedral stereogenic center (chiral center) of (I), give the priority of substituent’s
and its’ R/S designation.
for (c)
for
H
(a)
Br
Br
H
CH3
Cl
O
CH3
CH3
(I)
b) Considering (I) as a general formula for a moment, what is the total number of stereoisomers
possible for (I), considering all possible stereogenic (sp3 and sp2) centers? You must show some
brief work.
c) To the left of (I) and alongside it, draw a stereoisomer of (I) that is related to (I) as a
diasteriomer---draw carefully!
4
4.(06) A Belgian chemist recently described the first step of the following sequence as "an SN2
O
H
+
KO
Cr
O
O
120 / 1 hr
C
OK
Cr
O
Br
O
OK
DMSO
C
H
O
spontaneous
C
+
HO
Cr
O
alkyl
bromide
reaction of interest
reaction."
What feature would you study experimentally to establish that this step is indeed "SN2"? Briefly
describe an experimental study and what the outcome would be to confirm the S N2
designation. (There are at least two features that could be studied; recall lecture and text)
5. (18)
a) Draw the(3R,6E) stereoisomer of (II); the (3R, 6E) stereoisomer of (II) is the Aggregation
Pheromone of the Square-necked Grain Beetle(K. Mori, Ann., 159 (1990)). Be clear as you draw
the stereochemistry at appropriate locations, after first showing the priorities of groups at each
stereogenic center.
O
C
O
CH3 CH2
CH3
CH3
CH CH2 CH2 CH C
CH2 CH3
(II)
5
OK
b) In a recent synthesis of (III), the Odoriferous Principle of the Bartlett Pear (Syn Commun., 20,
633 (1990), two steps you would be able to describe. Fill in the necessary reagents, putting
them in order if required. Ask yourself: What has changed in the reaction? What remains the
same?
1)
OH
OH
O
2)
OCH2CH3
O
OCH2CH3
(III)
6.(O8) You have isolated an oil from a natural source and have established its molecular
formula as C10H16. There are two possible structural formulas, A and B. Using a simple chemical
reaction that we have discussed a number of times as a quantitative reaction, how can you
determine the structure of the oil to be A or B?
1. What is this simple reaction, in general terms? ("For Sale": 4 pts.)
2. When applied to C10H16, what result will you expect if the oil is
(A)
(B)
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7. (14) I noticed that I had drawn a meso stereoisomer (IV) in the Study Guide for this exam
although no plane of symmetry is seen in the conformation presented.
HO
H
H
OH
(IV)
a) What is the complete name of (IV), including designation of R/S for each stereocenter? No
need to list priorities of groups!
b) By simple rotation about what C-C bond in (IV) can the meso character of (IV) be seen,
ultimately? Designate this bond with an arrow: 
c) Alongside (IV) above, draw the conformation that clearly shows the meso character of the
stereoisomer, and carefully sketch where the plane of symmetry is located.
Alternatively, if it is difficult to proceed directly from (IV), simply draw the meso stereoisomer's
conformation with the plane of symmetry below, labeling the plane clearly.
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8.(13) The next prize in LOTTO will be 1.0 kilo of (V), valued at $67,800 (Aldrich.
Show those LOTTO operators that you know how to handle it. OUTLINE transformations of (V)
into (VI) and into (VII), maintaining as high an optical purity as possible in each transformation.
Use available reagents, and draw structures of any isolated intermediates in each
transformation. You will need at least two reactions on each route.
CH(CH3)2
HO
C
H
CH3
(CH3)2CH
H
(VI) you can't buy the R!
C
OH
CH3
S-(V)
(CH3)2CH
H
C
NH2
CH3
(VII)
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9.(14) Given structures (VIII), (IX) and (X):
CH3
CH3
CH3
O
CH2 O
S
O
CH3
CH2CH2
O
(VIII)
O
S
O
CH3
CH
O
(IX)
O
CH3
S
O
(X)
a) Give the relative rate 'order of (VIII)-(X) towards NaCN insofar as substitution is concerned,
listing the number of the fastest compound first, etc:
b) What is the fundamental reason for your choice of the slowest compound amongst (VIII)-(X)
insofar as substitution is concerned? Be specific and brief in your answer.
c) Which of the three compounds above is slowest insofar as elimination is concerned, under
the same conditions as mentioned in (a)? Why is this so?
d) Sketch the transition state for substitution, under the conditions with CN- reacting with (X),
assuming the reaction does occur:
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CH3
10.(17) Given the following set of reaction conditions:
CH3
CH3OH
I
(XI)
a) Write the structural formula(s) of the organic product(s) expected; if anything can be said
about relative amounts or products, assuming more than one organic product is formed, so
indicate.
b) There is one at least organic elimination product formed in the above reaction. Write a
mechanism accounting for its formation.
Potential
Energy
c) In the space below, sketch a reaction progress diagram for the mechanism you have drawn in
(b), labeling the axes, transition state, Energy of activation for the over-all reaction, and the
enthalpy of reaction; the "contents"(species present) of any "valley" ought briefly be indicated.
Reaction Progress
10
d) How will the rate of reaction of (XII) compare with the reaction rate of (XI) (above) under the
conditions given above? (be clear). Why is this order of reaction rates observed?
CH2I
H
(XII)
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