Chemistry Worksheet With Answers - Cem 351 2nd Exam/version A Page 2
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61. (20 pts) Consider the following eight representations of brominated hydrocarbons:
1-Bromo-2,2-dimethylpropane
CH
CBr
CH(CH
)
3
2
3
2
A
B
Br
(E) -(CH
)
CHCH=CHCH
Br
3
2
2
C
D
2-Bromo-4-methyl-1-pentene
3-Bromo-3-methylcyclopentene
E
F
CH
3
H
Br
H
C
H
3
Br
H
G
H
In this collection, identify…
–
a) (4 pts) The best substrate for S
2 reaction with azide ion (N
, a strong
N
3
nucleophile):__D__.
b) (4 pts) The best substrate for E1/S
1 reactions in H
O/EtOH:__F__.
N
2
c) (6 pts) A chiral substrate that undergoes neither substitutions nor eliminations__C__.
For your chosen compound, explain why it is so inert. Be sure to consider each
reaction mode (S
1, S
2, E1, E2) carefully.
N
N
Compound C is a bridgehead bromide in a bicyclo[2.2.1]framework. S
2 fails
N
because no nucleophile can approach from the (caged in) back (and it’s a
tertiary bromide anyway); S
1 and E1 fail because the bridgehead carbon
N
2
can’t achieve the planar sp
geometry required for cation formation; and E2
fails because it would make a twisted alkene whose p orbitals, held almost
perpendicular, can have little or no π-bonding (in violation of “Bredt’s rule” ).
d) (2 pts) Two representations of the same compound: __ E__and __ G__.
e) (4 pts) Use the box below to draw the product of your chosen S
2 reaction in (a):
N
N
3
2
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