Download Exam 2

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Simpson/
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Chern 242 (w 2016) exam #2A
1. (10 pts) Circle what is true about Substitution and elimination reactions.
a. Strong Bases (B") have conjugate acids (BH) that have small pKa values (<5)
® A good leaving group is a conjugate base of a strong acid
c. The Alcohol dehydration mechanism is also considered an Sn1 Mechanism
Q}
In an E2 mechanism the carbon with the leaving group changes hybridization
from sp3 to sp2 •
e. Alcohols can undergo an E2 mechanism only qpon addition of an acid catalyst.
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2. (10 pts) For the reaction below, identify which structure (A-G) would be the:
The intermediate for the E 1 mechanism:
The Transition state for the Sn1 mechanism:
D
D
---'=-----
The Transition state for the E2 mechanism: --------~
-1/2
Cl
-1/2
9CH3
I
CH3- - - o - H CH3---o-H
A
Cl
-1/2
B
OCH3
E9
[ CH,0 ~D]
c
+112
-1/2
H'_,
[ CH,O
D
I
I
3
H'
Cl
- 112
,OCH3
-o/
I
I
CH3--o
F
-1/2
,QCH
CH3
G
Cl-1/2
I
J
----------------
-
3. (18 pts-6 pts each) Draw the products for the following reactions.
--Also declare what the mechanism is for each reaction.
--Be sure to show the stereochemistry of the products.
Br
Solvent: Acetone
HO
4 (5 pts) The compound who below (called triphenyl methanol) undergoes an extremely
fast Snl reaction when reacted with HBr but doesn't form any El reaction productsExplain both observations; why Snl is unusually fast and why El doesn't occur.
9
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c-f
~ ~"~.J.?
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r
~ si,ll.t. -gbc"'+H.•' w'~ resonanct-1VCM
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IJb
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E,
~
poTYOS o.vtHI~L---
-------------------
-
b. (3 pts) Depict the carbocation of the substrate that would react the fastest.
fl.tson~'nct s/-eki/JJt~
6. a (5 pts) For the reaction below draw the major product of the E2 reaction with
compound A.
'E'
!""").
CH 30
h··
(..~
;=j
Bulky""''· E2
Cr1~ 0
A
b. (3 pts) Of the chair conformations shown below, circle the conformation that
represents the conformation that would be present for the E2 reaction above to occur.
Br
OCH 3
H
Br
CH30
H
OCH3
CH 3
H
Br
H
H
c. (3 pts) Draw an arrow ( -7) to the hydrogen (in the structure that you circled), that is
anti-periplanar to the leaving group.
7. (16 pts -8 pts each) For the reactions below, state ifthe mechanism is Sn1, Sn2, E2 or
E 1 and draw the product(s) produced by this mechanism. Be sure to show the pertinent
stereochemistry for the product(s).
p-CH,
Cl
Acetone solvent
Br
........
Type of mechanism_ _~...,
__
_ _ _ _ _ _ __
Br
Type of mechanism._ _£_,_,_/_eU.----=h_..t.tb---=crl1-=--~----
8. (9 pts) With the choices of the substrates, solvents and bases listed below put together
the fastest Sn2 reaction possible. Pick one compound from each category. Be sure to
draw the product ofyour reaction
solvent
Product
Substrate & base
Substrates
OH
~
9. Draw the arrow pushing mechanism for only one (A, B or C) Note some are worth
more than others. Of the following three mechanism questions--clearly state which
one you want graded.
A) (12 pts) Draw the mechanism and the major product for the reaction below
50
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+
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B (15 pts) draw the arrow pushing mechanism for the formation of the major
product shown. Clearly depict all intermediates. You do not have to depict
stereochemistry
H
/
CH3
-"
acid catalyst (H+)
+ CH3CH20H
" C-C/H
.
CHCH 2CH
3
I
:QH
..
~--
~
I
3
c.~c.4L-e-r-cl-\ :::c~-c~c.w
C.H3
+H20
C (14 pts). Draw the mechanism and all the products of the reaction of the alcohol with
thionyl chloride (SOCh) shown below. Be sure to depict the pertinent stereochemistry
of this reaction.
Part b (2 pts) (only answer if you drew the mechanism) Would this reaction go more
·
quickly or slowly ifwe used S0Bf2 instead ofSOCh? Briefly explain.
pyridine
._ hlove 9u1c.(J -
0
1) Ike
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o==s:::o
-t- Ct
Extra credits: (1 pts) What reaction mechanism did Julius Caesar refer to at the
,_.
r.>
"1i 1")
moment of his death in 44 BC.
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(1 pt) What is the name of your Instructors Dog?
(1 pt) Do you plan on taking Chemistry 251 or 251 (organic chem lab) in the summer?
Maybe
But~
e
Chern 24 2 (w 2016) exam #2B
1. (10 pts) Circle what is true about Substitution and elimination reactions.
(9 A good leaving group is a conjugate base of a strong acid
(!) The Alcohol dehydration mechanism is also considered an E 1 Mechanism
~ In an E 1 mechanism the carbon with the leaving group changes hybridization
from sp3 to sp2 •
@ Alcohols can undergo and Sn2 mechanism only upon addition of an acid catalyst.
e. Strong Bases (B-) have conjugate acids (BH) that have a small pKa value (<5) • Ff'O&l"t
2. (4 pts) a) For the Sn2 reaction below, identify which structure (A-F) would be the
~
Transition state for this reaction: ---=--b) (6 pts) Draw the reaction mechanism arrows and the product of this reaction
showing all the pertinent stereochemistry.
Sn2
TSr-
product
-112
OCH 3
1
-1/2
Br-----c
A
J~
0/
H
'H
CH 3 H
CH30
\
+1/2 /H
Br-----c------0
J'H
I:.
D
CH 3 ~
_112
OCH 3
-112
:
I
Br-----C-OH
B
J~
OCH 3
-l/2
I
+112/H
J-:.
'H
Br-----c------0
c
~
CH 3 H
CH 3 H
OCH 3
-l/2
I
-1/2 /H
Br----j~------0,
F
~~
CH3
H
H
-----------""____
----
""
___
---
3.(18 pts-6 pts each) Draw the products for the following reactions.
--Also declare what the mechanism is for each reaction.
--Be sure to show the stereochemistry of the products.
OH
Solvent: Acetone
Cl
4 (5 pts) The compound who below (called triphenyl methanol) undergoes an extremely
fast Snl reaction when reacted with HBr but doesn't form any El reaction productsExplain both observations; why Snl is unusually fast and why El doesn't occur.
\ ~lls~
~~~
sialo.k -g 6 rt\1-l~W~
f€Sono.n~ l.~>••ll.ftt &~1/ 3
4.~
&.n3en.t Yin~(-'.
./"-../Br
b. (3 pts) Depicr:;t
ilie c : & ;: B t h a : i l l ; s ;
~
6. a (4 pts) For
l'·~.h"
Br
f:t·
~
~J
c~
reaction below draw the product of the E2 reaction.
CH3
...
Bulky base, E2
b.(3 pts) Of the chair conformations shown below, circle the conformation that
represents the conformation that would be present for the E2 reaction above to occur.
H
H
H
H
c. (3 pts) Draw an arrow(~) to the hydrogen (in the structure that you circled), that is
anti-periplanar to the leaving group ..
7. (16 pts -8 pts each) For the reactions below, state if the mechanism is Sn1, Sn2, E2 or
E 1 and draw the product( s) produced by this mechanism. Be sure to show the pertinent
stereochemistry for the product(s).
OH
OH
Type of mechanism__£_)_~_h_&,_d_rr._t_l_tA.)
___
p-Br
OH
Acetone solvent
Br
Type of mechanism_ _S:_w_-v_________
8. (9 pts) With the choices of the substrates, solvents and bases listed below put together
the fastest E2 reaction possible. Pick one compound from each category. Be sure to
draw the product of your reaction
+
r/~
\
/c.-\-c~
(_~
solvent
6
Product
Substrate & base
Substrates
Solvents
OH
~
9. Draw the arrow pushing mechanism for only one (A, B or C) Note some are worth
more than others. Of the following three mechanism questions--clearly state which
one you want graded.
A) (12 pts) Draw the mechanism and the major product for the reaction below
OH
HO
B (15 pts) draw the arrow pushing mechanism for the formation of the major
product shown. Clearly depict all intermediates. You do not have to depict
stereochemistry
H
.
+ CH3CH20H
" C-C/H
/-'.
CH3
CHCH 2CH 3
I
OH
acid catalyst (H+)
+H20
C (14 pts). Draw the mechanism and all the products of the reaction of the alcohol with
thionyl chloride (SOCh) shown below. Be sure to depict the pertinent stereochemistry
of this reaction.
Part b (2 pts) (only answer if you drew the mechanism) Would this reaction go more
quickly or slowly ifwe used SOBrz instead ofSOCh? Briefly explain.
pyridine
N
0
+
Extra credits: (1 pts) What reaction mechanism did Julius Caesar refer to at the
moment of his death in 44 BC.
E 2-
.l. _ I ?
un... ~ .•
17
(1 pt) What is the name of your Instructors Dog?
b 1 n~ef""
(1 pt) Do you plan on taking Chemistry 251 or 251 (organic chem lab) in the summer?
No
Maybe