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Answered: - ddskdl skdldk dshsidhs? sskdmld dskdsldksld sjjdfjs dhfget


ddskdl skdldk dshsidhs?

sskdmld

dskdsldksld sjjdfjs dhfgetdb djdsjldand dhdgsda ?


CHM1321
?Midterm
2
2015

 


 



 


 

Page
2
of
9

 


 

Part
A

 



 

1. Give
the
conjugate
acid
and
base
of
the
following
species:

 



 

CH3NH2

 

CH3NH3+

 

conjugate
acid

 


 

CH3NH2?

 

conjugate
base

 


 



 

2. A
catalyst
that
lowers
the
activation
energy
barrier
by
~12
kJ/mol
will
accelerate
the
reaction
rate

 

roughly
by
a
factor
of:

 


 



 


 

2

 


 



 


 

10

 


 



 


 

50

 


 



 


 

100

 


 



 

O

 

3. Indicate
the
most
electrophilic
site
in
the
following
molecule:

 



 



 



 



 



 

4. Identify
the
following
transformations
as
either
oxidations
or
reductions.

 

H H

 

H

 


 

C

 


 

H Cl

 

C

 


 

H

 


 

H

 


 

H H

 


 

C

 


 

H

 

C

 


 

Cl

 


 

C

 

H

 


 

H H

 


 

oxidation

 


 



 


 



 


 

H

 


 

C

 

H

 


 



 


 

C

 


 

C

 


 

NH 2

 

O

 


 



 


 

H

 


 

H H

 

H

 


 

H

 


 

H H

 


 



reduction

 


 

120

 


 

O

 


 

H H

 


 

H

 


 



 


 



 


 

O

 


 



 


 

C

 


 

O

 

H

 


 

C

 

H

 


 




oxidation

 


 



 


 



 

5. The
awesome
German
word
used
to
indicate
a
switch
in
polarity
at
a
carbon
atom
(from
positive
to

 

negative,
or
visa
versa)
is
______UMPOLUNG__________.

 



 

6. Organopotassium
reagents
are
not
used
as
nucleophiles
in
organic
synthesis
because
_______________

 

______too
reactive/explosive/too
dangerous______________________.

 



 

7. Include
all
lone
pairs
of
electrons
and
add
electron-??pushing
arrows
as
needed
to
complete
the
following

 

reaction:

 



 

H

 


 



 


 

+

 


 

O

 


 



 


 

H

 


 

C

 


 

C

 


 

H

 


 

H

 


 

CH 3

 


 

CH 3

 


 

Br

 


 

H 2O

 


 

+

 


 

+

 


 

Br

 


 



 


 

CHM1321
?Midterm
2
2015

 


 



 


 

Page
3
of
9

 


 

Part
B

 



 

8. (4
pts)
Clearly
indicate
the
specific
relationship
(structural
isomers,
conformers,
enantiomers,

 

diasterisomers)
between
molecule
A
and
structures
B
through
E.

 

OH

 


 

OH

 

OH

 


 

OH

 


 

OH

 


 

A

 


 

B

 


 

D

 


 

C

 


 

E

 


 

A
and
B
are:
DIASTEREOISOMERS

 


 

A
and
C
are:
ENANTIOMERS

 


 

A
and
D
are:
CONFORMERS

 


 



 


 

A
and
E
are:
STRUCTURAL
ISOMERS

 


 



 

9. (4
pts)
For
the
acid-??base
reaction
below:

 

a. Draw
a
mechanism
and
the
expected
products.

 

b. Identify
the
acid,
base,
conjugate
acid,
and
conjugate
base.

 

c. Does
the
equilibrium
favour
the
starting
materials
or
products?
Justify
your
answer.

 


 

O

 

H 3C

 


 



 


 

C

 


 

H

 

+

 

CH 3

 


 

F 3C

 


 

CH 3

 


 









ACID

 


 

C

 


 

H 3C

 


 

CF 3

 


 

CF 3

 


 


























BASE

 


 

H

 


 

O

 


 

O

 


 

C

 


 

+

 

CH 3

 


 

F 3C

 


 

CH 3

 


 





























CONJUGATE
BASE

 


 

O

 

C

 


 

CF 3

 

CF 3

 


 



 






CONJUGATE
ACID

 


 

This
reaction
is
REACTANT-??FAVOURED.
The
fluorine
atoms
on
the
base
help
stabilize
its
negative
charge

 

(with
respect
to
the
conjugate
base)
via
the
INDUCTIVE
EFFECT.
Thus,
the
perfluorinated
tert-??butanol

 

((CF3)3COH)
is
the
stronger
acid
of
the
two,
and
the
equilibrium
direction
is
RIGHT
to
LEFT.

 



 



 

10. (3
pts)
Providethe
structures
of
the
compounds
A
to
C
below.

 

CH 3CH2CH2MgBr/ether

 


 

A

 


 

cyclohexanone/ether

 


 

B

 


 

H 3O+ /H2O

 


 

C

 



 


 

A

 


 

B

 



 

(+ CH3CH2CH3)

 


 

C

 

HO

 


 

BrMgO

 


 

MgBr

 


 



 


 



 


 

CHM1321
?Midterm
2
2015

 


 



 


 

Page
4
of
9

 


 

11. (4
pts)
Draw
the
full
mechanism
and
show
the
final
product
of
the
following
transformation.
Clearly

 

show
stereochemistry
(if
necessary).

 

Br O

 

Br

 


 

H

 

H

 


 

1) 2 equivalents of LiC

 


 

CCH 3/ether

 


 

2) H 3O+ /H2O

 


 

H

 


 

?

 


 



 


 

HO

 


 

Br O

 


 

Br O

 

Br

 


 

H

 

H

 


 

H

 


 

H

 


 

H 3C C C Li

 

(2nd equivalent)

 


 

NOTE: back

 

face attack

 


 

O

 


 

OH

 

Br

 

H

 


 

2 H 2O

 


 

H

 


 

Br

 


 

C CCH 3

 


 

H O

 

H

 


 

Br

 


 

+

 


 

H

 


 

Li O

 


 

H 3C C C H

 


 

H O

 


 

H 3C C C Li

 

(1st equivalent)

 


 

Br

 


 

H

 


 

H O

 

H

 


 

C CCH 3

 


 

H

 


 

H

 

H

 


 

H

 


 

HO

 


 

Li

 

Br

 


 

H

 


 

Li O

 


 

H

 


 

I?m showing both

 

protonations at once, but

 

it?s ok to show them one

 

at a time.

 


 



 


 

O

 

12.
(5
pts)
The
molecule
shown
is
a
form
of
penicillin,
the
antibiotic
discovered

 

HO C

 

by
Alexander
Fleming
in
1928.

 

O

 

A*

 

a. Identify
the
stereocentres
in
penicillin,
and
label
them
as
R
or
S.

 

N

 

O

 

H 3C

 

B

 

b. What
is
the
maximum
number
of
possible
stereoisomers
of
this

 

H 3C

 

S *

 

molecule?

 

* N

 

CH 3

 

H C H

 

c. Draw
the
enantiomer
of
this
structure.

 



 

3

 

A

 

B

 

C

 

2

 


 

3

 

HO

 


 

O

 

C

 


 

H 3C

 

H 3C

 


 

H

 


 

R

 


 

NR 2

 


 

4

 


 

CHR

 


 

RS

 


 

NR 2 1

 


 

1

 


 

2 S

 


 

This chiral centre is S.

 


 

H

 

4

 


 

3

 


 

This chiral centre is R.

 


 



 


 

NHR 1

 


 

H

 

4

 


 

NHR

 


 



 

Max
number
of
stereoisomers
=
23
=
8.
The
enantiomer
is:


 


 



 


 

HS

 


 

R2

 

C

 

2

 


 

O

 


 

C

 


 

This chiral centre is R.

 


 

HO

 


 

O

 

C

 

O

 

N

 


 

H 3C

 

H 3C

 


 

S

 

H

 


 

O

 

N

 

H

 


 

CH 3

 


 



 


 

CHM1321
?Midterm
2
2015

 


 



 


 

Page
5
of
9

 


 

Part
C

 



 

13. (4
pts)
Provide
a
retrosynthesis
for
the
following
compound,
using
1-??bromoethane
as
a
reagent.
Show

 

all
reagents
required.

 



 

OD

 


 

OMgBr

 

+

 


 

D 2O

 


 

O

 

+

 


 

MgBr

 


 

Br

 


 

+

 


 



 


 

Mg

 


 



 


 



 



 

14.
(4
pts)
Draw
the
full
mechanism
and
the
final
products
of
the
following
transformation.
Clearly
show

 

stereochemistry
(if
necessary).

 



 

O

 


 

OH ?/H2O

 


 



 


 



 



 


 



 


 



 

O

 


 

O

 

+

 


 

O

 


 

H

 


 

OH

 

+

 


 

O H

 

OH

 


 



 



 


 

H

 


 

O H

 


 

OH

 


 



 



 


 

CHM1321
?Midterm
2
2015

 


 



 


 

Page
6
of
9

 


 

15. An
important
part
of
organic
synthesis
is
the
isolation
and

 

purification
of
the
final
product.

 

a. (3
pts)
At
right
is
an
incorrect
experimental
setup
for
a

 

fractional
distillation
(the
support
has
been
left
out
for

 

simplicity).
Identify
the
3
errors
and
suggest
how
they

 

may
be
corrected.

 

b. (1
pt)
What
effect
does
a
decrease
in
atmospheric

 

water out

 

pressure
have
on
the
boiling
point
of
a
liquid?

 

c. (2
pts)
A
student
wishes
to
purify
the
final
product
of
a

 

water in

 

Grignard
reaction
by
recrystallization.
She
dissolves
80

 

mg
of
her
product
in
5
mL
of
methanol
at
25
?C.
She

 

cools
the
solution
in
an
ice
bath
and
obtains
crystals.

 

water in

 

The
crystals
are
recovered
by
filtration
and
rinsed
with

 

0.5
mL
of
ice-??cold
methanol.
After
drying,
the
weight
of

 

the
crystals
is
only
5
mg.
Explain
why
was
the
recovery

 

so
poor
and
suggest
an
alternative.

 

water out

 



 



 



 



 



 



 



 

ERRORS:
there
are
several
small
errors,
here
are
some
examples:

 

1)
On
the
column,
the
WATER
INLET
AND
OUTLET
ARE
INCORRECT
?
they
need
to
be
reversed,
so
that
the

 

entire
column
fills
with
cooling
water
(alternatively,
you
could
say
water
is
not
needed
on
the
column)

 

2)
The
THERMOMETER
IS
TOO
HIGH
in
the
joint:
it
will
not
accurately
read
the
temperature
of
the
gas

 

vapours
ecaping
the
column
and
must
be
lowered.

 

3)
The
receiving
flask
is
an
Erlenmeyer
flask:
it
should
be
a
ROUND
BOTTOM
FLASK
(flat-??bottom
flasks
have

 

larger
liquid
surface
areas
and
thus
might
encourage
evaporation
of
distillate).

 

4)
The
column
is
missing
its
PACKING
MATERIAL
needed
for
the
fractional
distillation.

 

5)
The
applied
VACUUM
is
missing
from
the
TAKEOFF
ADAPTER.

 



 

Decreasing
atmospheric
pressure
means
the
liquid?s
vapour
pressure
will
match
atmospheric
pressure
at
a

 

lower
temperature.
Thus
the
boiling
point
will
DECREASE.

 



 

The
product
of
a
Grignard
reaction
is
an
ALCOHOL.
Thus,
using
methanol
as
a
recrystallization
solvent
is
a

 

poor
choice
because
it
seems
that
the
alcohol
product
is
SIGNIFICANTLY
SOLUBLE
in
this
solvent
(too
similar

 

polarities).
Thus,
it
would
be
wise
to
choose
a
slightly
LESS
POLAR
SOLVENT
in
order
to
recover
more
solid

 

product.

 



 



 


 

CHM1321
?Midterm
2
2015

 


 



 


 

Page
7
of
9

 


 

16.
(6
pts)
The
reagent
below
is
diisobutylaluminum
hydride,
or
DIBAL-??H.
Like
sodium
borohydride,
it
is
a

 

source
of
nucleophilic
hydride.


 

H

 

Al

 


 



 

a. Draw
the
full
mechanism
for
the
reaction
of
DIBAL-??H
with
acetone
(2-??propanone),
along
with
the

 

required
aqueous
acid
workup.

 

b. Unlike
NaBH4,
reductions
performed
with
DIBAL-??H,
require
equimolar
amounts
of
DIBAL-??H
and

 

substrate.
Can
you
explain
this
difference?

 


 



 


 

O

 


 

Al

 


 

H

 


 

O

 


 

H

 


 

O H

 


 

+

 


 

H

 

H

 


 

H O

 


 

H O

 


 

H

 


 

OH

 

+

 


 

O H

 


 

H

 


 

H

 


 

O H

 


 

Al

 


 

H

 


 

Al

 


 

H

 


 

O H

 


 

H

 


 

Al

 


 

O

 

Al

 


 

H

 


 

H

 


 

O H

 

Al

 


 

+

 


 



 



 

NaBH4
provides
4
equivalents
of
H?
(so
you
only
need
one
quarter
of
reducing
agent);
DIBAL-??H
on
the
other

 

hand,
has
only
one
hydride
to
give
?
thus,
you
must
use
as
much
reducing
agent
as
the
substrate.

 



 

BONUS
?
3
pts

 



 

OH

 

The
molecule
at
right
is
a
diprotic
acid
called
?squaric
acid?.
In
its
dianionic
form,
experimental
O

 

data
shows
that
all
the
C?C
bonds
are
of
the
same
length
and
all
the
C?O
bonds
are
of
the

 

same
length.
Provide
an
explanation
why.

 

O

 

OH

 



 

Once
doubly
deprotonated,
we
can
see
why
squaric
acid
is
such
a
good
acid:
it
has
4
equivalent
resonance

 

structures:

 

O

 


 

OH

 


 

O

 


 

OH

 


 

? 2 H+

 


 

H

 


 

O

 


 

O

 


 

O

 


 

O

 


 

O

 


 

O

 


 

O

 


 

O

 


 

O

 


 

O

 


 

O

 


 

O

 


 

O

 


 

O

 


 

O

 


 

O

 


 

!?

 


 

O

 


 

O !?

 


 

O

 


 

O

 


 

2?

 


 

RESONANCE HYBRID:

 


 

!?

 


 

!?

 


 

From
the
resonance
hybrid,
we
see
that
all
the
C?C

and
all
the
C?O
bonds
are
equivalent!

 



 



 


 



 


 

 


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