CHEM 233, Fall 2015
PRINTED
ANSWER
FIRST NAME
Midterm #3
PRINTED
KEY
LAST NAME
Ian R. Gould
ASU ID or
Posting ID
Person on your RIGHT (or Aisle)
Person on your LEFT (or Aisle)
WHICH CLASS ARE YOU REGISTERED FOR: ONGROUND OR HYBRID:
nomen
1_____________/12
........
• PRINT YOUR NAME ON EACH PAGE!
acid/base
2_____________/30
........
• READ THE DIRECTIONS CAREFULLY!
LAB
3_____________/34
........
• USE BLANK PAGES AS SCRATCH PAPER
reactions
4_____________/40
........
work on blank pages will not be graded...
mxn
5_____________/35
........
•WRITE CLEARLY!
BDE
6_____________/24
........
• MOLECULAR MODELS ARE ALLOWED
• DO NOT USE RED INK
H
Interaction Energies, kcal/mol
He
Li Be
B
Na Mg
K
Total (incl Extra)________/175+5
Extra Credit_____/5
• DON'T CHEAT, USE COMMON SENSE!
Ca
C
N
O
Al Si P
Sc Ti V
Cr Mn Fe Co Ni Cu Zn
Rb Sr
Y
Zr Nb Mo Tc Ru Rh Pd Ag Cd
Cs Ba
Lu Hf Ta W
Re Os Ir Pt Au Hg
small range
range of values
broad peak
O H
C N
N H
C O
F
S
Ne
H
Kr
H/Me
~1.4
Et/Me
~0.95
In Sn Sb Te I
Xe
Me/Me
~2.6
i-Pr/Me
~1.1
Tl Pb Bi Po At
Rn
Me/Et
~2.9
t-Bu/Me
~2.7
Infrared Correlation Chart
usually
strong
C
H
C
O
1735
CH
11
220 O
10
200
R C OH
C
2000
1500
O
–OCH2–
NMR Correlation Charts
–H2C NR2
C CH2
O
C
8
160
C CH3
–H2C X
Aromatic Ar H
mainly 8 - 6.5
9
180
NR2
1650
amine R NH2 variable and condition
alcohol R OH dependent, ca. 2 - 6 δ
(δ, ppm)
O
1710
2500
O
C H
1600
O
2200
3000
O
R C OH
OR
C
O
C O H
3500
1680
C
broad ~3000
(cm-1)
N
C
N
C
2850–2960
broad ~3300
1600–1660
H
broad with spikes ~3300
O H
C
C
O
2200
C
~0.9
Ga Ge As Se Br
2720–2820
2 peaks
3000–
3100
N H
Me/Me
Ar
H
C
3300
~1.0
Cl
O
C H
Gauche
Eclipsing
H/H
7
140
6
120
5
100
4
80
Aromatic
CR2
3
60
RC
CR
Alkyl
3Y > 2Y > 1Y
2
40
–OCH2–
R C N
R2C
C CH
1
20
0
0
Alkyl 3Y > 2Y > 1Y
C X
C NR2
-2-
CHEMISTRY 233, Fall 2015, MIDTERM 3
NAME
Question 1 (12 pts.) Give the IUPAC name for the following structure. Be sure to include
stereochemistry if appropriate.
Br
1
2
3
4 5
6
5-bromo-4-ethyl-3,7-dimethyl-(3E)-octene
7
8
grading -2pts each error, do not propagate errors
Question 2 (30 pts) For the following Bronsted acid/base equilibrium
a) add the curved arrow pushing for reaction in both directions and ADD ALL REASONABLE
MISSING RESONANCE CONTRIBUTORS AS APPROPRIATE
b) indicate the stronger and weaker acid and base on each side and give a brief explanation
c) indicate which reaction is faster AND on which side the equilibrium lies
d) indicate which acid has the smaller and which the larger pKa
O
O
slower
H
H
+
+
weaker acid
larger pKa
faster
weaker
base
equilibrium on THIS side
stronger
base
stronger acid
smaller pKa
O
the base on the left is weaker because the electron energy is lower, the charge is delocalized
onto the more electronegative oxygen, compared to carbon on the right
e) Draw an energy diagram with properly labelled axes for the equilibrium shown above, showing the
activation energy in BOTH directions and draw the transition state
O
H
‡
energy
EaR>L
EaL>R
reaction
coordinate
‡
-3-
CHEMISTRY 233, Fall 2015 MIDTERM 3
NAME
Question 3 ( 34 pts.)
a) For reactions A and B, add the curved arrows that illustrate bond-making and bond-breaking,
indicate the Lewis acids bases (LA/LB) and whether they are also Brønsted acids/bases (BA/BB)
N
O
O C
C
LA
(A)
N
LB
O
O
C N
LB/BB
H C
(B)
N
LA/BA
H
b) Draw a reaction energy diagram for both reactions ON THE SAME DIAGRAM (do not draw
2 diagrams) and label the axes. Indicate which curve is for which reaction and indicate the
activation energies for each reaction and include a drawing of both transition states and
indicate their positions on the diagrams.
‡
O
Energy
N
C
(B)
H
(B)
E
a
O
O
Ea(A)
+
H C N
C N
‡
O
C
N
(A)
O
C
reaction coordinate
N
c) Would you expect reactions and be to be exothermic or ednothermic (they can be be
different)? Give a brief explanation.
Reaction A is exothermic since it breaks a pi-bond and makes a sigma-bond and it puts the
negative charge on the more electronegative oxygen
Reaction B is endothermic compared to B since it breaks a sigma bond and puts the
negative charge on carbon and the charge was on an sp hybridized carbon in the reactant
and sp3 hybridized carbon in the product, the charhe in the reactant is also stabilized by
the electronegative nitrogen
d) Briefly explain which reaction is faster and which has the EARLIER transition state in terms of
the Hammond postulate.
reaction A is faster because it is more exothermic, the Hammond postulate says that the more
exothermic reactions have smaller activation energies and earlier transition states
-4-
CHEMISTRY 233, Fall 2015, MIDTERM 3
NAME
Question 4 (40 pts.) Give the missing major organic products OR reagents/conditions as
appropriate for each of the following reactions
clearly indicate relative sterochemistry in the products where relevant
Ph
Ph
H
1. BH3.THF
a)
2. –OH/H2O2
Ph
H
OR
OH
OH
HBr
b)
Br
CCl4
inert solvent
1. H2O/Hg(OAc)2
c)
2. NaBH4
HO
H2
d)
Me
Me
Pd/C
Me
Br2
e)
MeOH
H Me
H
OR
Br
OMe
Br
Extra Credit (5 pts) Dr. Gould had a conversation with his daughter about which topic?
cisand
trans-
saturated
and
unsaturated
acids
and
bases
Markovnikov
and
Anti-Markovnikov
OMe
-5-
CHEMISTRY 233, Fall 2015, MIDTERM 3
NAME
Question 5 (35 pts) Give the curved-arrow pushing fo the following reaction. For each
INTERMOLECULAR, indicate the Lewis acid/base (LA/LB) and Bronsted acid/base (BA/BB)
where appropriate.
Br
H Br LA/BA
LB/BB
HBr
CCl4
inert solvent
LB
H
Br
LA
grading: use common sense, 1/2 right = 1/2 points etc.
depends upon the mxn
b) How many steps are there in your mechanism? ____________
depends upon the mxn
c) How many transition states are associated with your mechanism? ____________
d) Draw a reaction energy diagram for your mechanism, label the axes, indicate the positions of
the reactants, prodicts and any intermediates (don't redraw the structures, you can circle the
items on the mechanism and use arrows, or use symbols such as I1 for intermediates 1 etc.).
Indicate the ACTIVATION ENERGY FOR EACH STEP, the REACTION EXOTHERMICITY and
the RATE DETERMINING STEP.
‡
Energy
‡
Ea2
Ea1 rate
detn
step
reactants
‡
Ea3
I1
exothermicity
product
reaction coordinate
e) Draw below the TRANSITION STATE for the rate determining step (only)
‡
H
Br
CHEMISTRY 233, Fall 2015 MIDTERM #3
-6-
NAME
Question 6 (24 pts.) For each of the C-H bonds A and B indicated in the structures below:
a) Give the curved arrow pushing for HOMOLYTIC bond dissociation of each bond
b) give the products of homolytic bond dissociation, including all reasonable resonance contributors
as appropriate (it is not necessary to draw the curved arrow pushing showing how different
resonance contributors relate)
A
THIS bond
H
H
1°
2°
3°
B
THIS bond
2°
H
H
b) BRIEFLY explain which bond, A or B, has the smallest bond dissociation energy, and why
the radical formed upon dissociation of bond A is centered on primary and secondary
carbons, whereas that from B is centered on secondary and tertiary carbons, the energy of
the non-bonding electron in the radical from B is lower than that from A, the radical takes less
energy to form, the dissociation energy for B is this lower than that for A
c) Draw an energy versus C-H bond separation distance (rR-H) diagram for homolysis of these
two bonds, on the same diagram, and be sure to label the axes. Clearly indicate which diagram
refers to which bond cleavage and indicate the two bond dissociation energies on the diagram.
Energy
BDE B
BDE A
rR–H