Unformatted text preview: CHEMISTRY 2211
December 11, 2008
SCORE Be sure to read each question carefully. Partial credit will be assigned where appropriate.
To receive full credit you must answer the question completely. u (21,L lin el good luck!! /6 oc 1. (20 points) There are eleven c y clic isomers of molecular formula C 4 H 8 0 that contain
chiral carbons. Draw the two constitutional isomers that contain only one chiral carbon. (You do not
need to draw the enantiomer of each constitutional isomer.) 12- ct Using wedges and dashes to indicate stereochemistry, draw three stereoisomers
containing two chiral carbons that exist as one pair of enantiomers and one meso
diastereomer.,Ci the enantiomers._Th„ NCAttir 9.
0 \0: Using wedges and dashes to indicate -sfireochem stry, draw four stereoisomers
containing two chiral carbons that exist as two diastereomeric pairs of enantiomers. 2 2. (8 points) Draw a structure for each of the following compounds in its most stable chair
CH3 ,.CH3 (H3C)3C .CH3
CH3 On the templates below, draw the two chair conformations of the sugar a-(+)glucopyranose, one form of the sugar glucose. and circle the form that is the major form at
equilibrium. Note: C-1 is indicated in each structure.
HO., HO 'OH
OH a-(+)-glucopyranose otA 3 hAniefo NAME last, first \6 - 810# 3. (12 points) Draw a Newman projection for the most stable conformer of l-chloro-21methylpropane (isobutyl chloride) sighting down the C 1 -C 2 bond.
(-1 How many non-hydrogen gauche interactions are present? Draw a Newman projection for the least stable staggered conformer of isobutyl chloride
sighting down the C 1 -C 2 bond. 3 How many non-hydrogen gauche interactions are present? Draw a Newman projection for the most stable conformer of 1-chloro-2-methylpropane
(isobutyl chloride) sighting down the C 2 -C 3 bond. C LI
How many non-hydrogen gauche 1-4
interactio nsare present? .+6,7 4 4. (18 points) Consider the following equilibrium reaction that exhibits the free-energy diagram shown below. A reaction coordinate Which compound is present in greatest amount when the reaction comes to equilibrium? Which compound is present in least amount when the reaction comes to equilibrium? What is the rate-limiting step of the reaction? to C C Using a vertical arrow, label on the reaction coordinate diagram the standard free energy of
reaction for the overall A —0" D reaction.
Which reaction of compound C is faster: C B or C D? Which reaction of compound B is faster: B C or B A? For the forward reaction, which individual step will exhibit a transition state geometry most
like the reactant for that step? For the forward reaction, which individual step will exhibit a transition state geometry most
like the product for that step? In which direction, forward or reverse, will the equilibrium shift in response to an increase in
AA rrI 6k mr),11/9/1 NAME
last, first (9r1t9-t
810# 5. (12 points) Give complete, stepwise and detailed mechanisms for the following reactions. Note: Describe in detail the
bromination and ring formation
steps. You do not need to
describe the mechanism of the
elimination step. ctr2 OH 2. elimination step HO H2SO4(concentrated)
0 Hint: Describe the mechanism
of the ketone formation step
only. You do not need to
describe the mechanism of the
elimination step. 6 6. (15 points) Outline a synthesis for each of the following compounds starting from acetylene
and any other necessary reagents. Draw a structure for the product of each step in the
7 H Br (2S,3R)-2,3-di br omopentane 2
HCECH HCECH CH3(C1-12)7COOH NAME
last, first I
810# 7. (20 points) Complete the following reactions by providing the starting material, necessary
reagent(s), or major product.
DCH3 CH /CH2OH Br
r CH2Br aCH2 c
aCH2OH crCH2 orCH3
Br 1. Mg
CH2CH3 ‘-‘1 ,Litt CH3CH2Cu + Lil 2 equivalents (C 17 H 1606) heat 8 8. (15 points) Treatment of the diene below with NBS yields five products. Four of the
products contain chiral carbons, but the product mixture is optically inactive. Draw
structures for the five expected products. Per Draw the hybrid intermediate structure from which all of the above products were derived.
F \\\NN,7 Explain in 15 words or less why the product mixture is optically inactive.
le:2&J L.Y C
L11. r A rNa Se% c. i1 /J—\
NAME 12 .)1/— A-3h„r-)./
last, first 810# 9. (10 points) Treatment of benzyl bromide with either CH 3 0 or CH 3 OH yields the same
product. When C1-1 3 0 is used, the rate of product formation depends on the concentration of
CH 3 0 but when CH 3 01-1 is used 4,1;:. of product formation does not depend on the
concentration of CH3OH.
Br benzyl bromide
Show the reaction mechanism for the reaction of benzyl bromide with CH 3 0 and use it to
explain the dependence of the reaction rate on the concentration of CH 3 0 . .1 - 4() •,6 L._ V%50 ej
rr, ulY1 r\f plePte-e-ti-, e--S 14- /4 14,‘ Bt'• D 5 6 - - -C-- - leek)
Show the reaction mechanism for the reaction of benzyl bromide with CH 3 OH and use it to
explain why the reaction rate is independent of the concentration of CH3OH.
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