Download First Midterm Answer Key

CHEM 233, Fall 2013
Midterm #1
answer
PRINTED
FIRST NAME
PRINTED
LAST NAME
Ian R. Gould
ASU ID or
Posting ID
key
Person on your LEFT (or Aisle)
Person on your RIGHT (or Aisle)
BDE
1___________/30
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• PRINT YOUR NAME ON EACH PAGE!
charges
2___________/18
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• READ THE DIRECTIONS CAREFULLY!
A.O.s
3__________/22
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• USE BLANK PAGES AS SCRATCH PAPER
structures
4__________/43
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work on blank pages will not be graded...
hybrid
5__________/20
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•WRITE CLEARLY!
dipoles
6__________/20
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• MOLECULAR MODELS ARE ALLOWED
M.O.s
7__________/22
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• DO NOT USE RED INK
• DON'T CHEAT, USE COMMON SENSE!
Total (incl Extra)________/175+5
Extra Credit_____/5
H
He
Li Be
B
N
O
F
Ne
Na Mg
Al Si P
S
Cl
Ar
H/H
~1.0
Me/Me
~0.9
Ga Ge As Se Br
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
K
Ca
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
small range
range of values
broad peak
Re Os Ir Pt Au Hg
O H
C N
N H
C O
C
Interaction Energies, kcal/mol
C
H
O
C H
H
C
N
O
OR
amine R NH2 variable and condition
alcohol R OH dependent, ca. 2 - 6 δ
11
220 O
10
200
Aromatic Ar H
mainly 8 - 6.5
C CH3
R C OH
–H2C NR2
C CH2
9
180
O
C
8
160
H
O
–OCH2–
NMR Correlation Charts
7
140
6
120
5
100
R2C
Aromatic
CR2
C CH
4
80
3
60
2
40
–OCH2–
R C N
RC
H
~15
C C
1500
–H2C X
(δ, ppm)
~2
H
NR2
1650
2000
H
H
C
1710
2500
O
C H
~8
~2
C C
O
2200
3000
O
R C OH
H
~10
H
1600
O
C
O
C O H
3500
H
C C
1735
CH
broad ~3000
(cm-1)
~7
H
C
2850–2960
broad ~3300
H
1680
C
H
broad with spikes ~3300
O H
H H
C C
C
2200
C
N
O
2720–2820
2 peaks
3000–
3100
N H
C
1600–1660
H
C
3300
Approximate Coupling
Constants, J (Hz), for
1H NMR Spectra
Infrared Correlation Chart
usually
strong
C
Gauche
Eclipsing
CR
Alkyl
3Y > 2Y > 1Y
1
20
0
0
Alkyl 3Y > 2Y > 1Y
C X
C NR2
-2-
NAME
CHEMISTRY 233, Fall 2013, MIDTERM #1
Question 1 (30 pts.) For the C-C bond A, and the C-H bonds B and C indicated by the arrows
a) Draw the curved arrow pushing describing homolytic bond cleavage, and draw the products of
each homolytic bond cleavage reaction
b) Rank the bond dissociation energies for A, B and C and give a brief explanation
c) For the C-H bonds B and C ONLY, draw energy versus C-H separation distance diagrams
for bond dissociation on the same diagram (use the provided axes), clearly indicate which is
which
d) Indicate the
A magnitudes of the BDEs for B and C on the diagrams
H
A
<
smallest
BDE
H
<
B
largest
BDE
H
H
H
C
H
H
B
H
H
H
C
H
H
C-C bonds are weaker than C-H bonds because they are made by overlap of larger atomic
orbitals, which results in poorer overlap, higher energy electrons in the bond, A is the weakest
bond
the carbon is sp2 hybridized in B compared to sp3 hybridized in C, sp2 hybrid A.O.s are smaller,
lower in energy, the electrons in bond B are lower in energy than in C, B is the strongest bond
B
Energy
C
BDE (B)
BDE (C)
rR–H
Extra Credit (5 pts.) In the "Organic Chemistry in Real Life" pages, anti-bonding molecular
orbitals were described as playing an important role in which of the following
color
burning hydrocarbons
ATP energy conversion
-3-
CHEMISTRY 233, Fall 2013, MIDTERM #1
NAME
Question 2 (18 pts.) Add any missing formal changes to the following structure (all nonbonding electrons are included).
H
H
O
N
H
N
N
H
H
O
H
N
H
H
aqueous solution form of the amino acid arginine
Question 3 (22 pts.) Given the following picture of the Ψ for a 3p A.O., give a plot of Ψ
versus distance from the nucleus, r (use the provided axes). Indicate the positions of the
nodes BOTH on the picture AND on your plot. STATE THE NUMBER OF NODES that
the wavefunction for this orbital has (use the nodal theorem).
spherical node 2
spherical node 2
r
plane node 1
plane node 1
spherical node 2
Ψ
0
r
BOTH are equally correct
OR
r
spherical node 2
0
r
you did not need to differentiate the spherical and plane nodes, but you did have to know
that the total number of nodes was TWO
-4-
CHEMISTRY 233, Fall 2013, MIDTERM #1
NAME
Question 4 (43 pts.) For the molecular formula C4H7N << this was suppsoed to be C3H5N!!
a) Give the degrees of unsaturation
2 degrees of unsaturation
b) Draw ONE PAIR of stereoisomers that obey the normal rules of valence for each atom. Include
all non-bonding electrons. You can draw Lewis structures or line-angle structures (your choice). If
you draw line-angle structures, don't forget to include the H atoms that are normally included as
part of the functional groups.
NH2
NH2
OR
and
NH2
and
NH2
there are many possibilities, too many to list......
c) Draw FIVE ADDITIONAL structural isomers that obey the normal rules of valence for each atom.
Include all non-bonding electrons. You can draw Lewis structures or line-angle structures (your
choice). If you draw line-angle structures, don't forget to include the H atoms that are normally
included as part of the functional groups. DO NOT INCLUDE ANY STRUCTURE YOU INCLUDED
AS PART OF YOUR ANSWER TO PART b) OF THIS QUESTION!
NH2
NH2
N
N
N
N
NH
H
N
N
NH
N
4-ring structures and 3-ring structures etc. etc.
there are many possibilities, way too many to list......
CHEMISTRY 233, Fall 2013, MIDTERM #1
-5-
NAME
Question 5 (20 pts.) For the oxygen atom in the structure given below, give the hybridization
AND make a list of the hybrid atomic orbitals and explain exactly how the oxygen makes use
of each one (e.g. it uses X A.O. to make a σ-bond to atom Y, etc.)
sp2
H
sp2 - makes a σ-bond to hydrogen
O
sp2 - makes a σ-bond to carbon
sp2 - holds the non-bonding pair of electrons
p - makes a π-bond to carbon
Question 6 (20 pts.) ON TOP OF the structures of acetone and acetonitrile shown below,
draw the molecular dipole moments (you should show the direction only, your dipoles do
not need to represent their magnitudes). The dipole moment of acetonitrile is LARGER than
that for acetone, give a brief explanation for this fact.
O
+ H3C
+
acetone
smaller molecular
dipole moment
C
N
acetonitrile
LARGER molecular
dipole moment
π-electrons are more polarizable than σ-electrons, even though N is less electronegative than
O, the C-N triple bond has more π-electrons (2 π-bonds compared to 1), and thus the
electrons are more polarized, the dipole moment is thus larger
Question 7 (22 pts.) For the indicated localized molecular orbitals, draw a picture of the Ψ or Ψ2
as requested, directly ON TOP of the structures. In each case also give the atomic orbitals
that are used to "build" the molecular orbitals. All non-bonding electrons are shown.
Indicate the positions of any nodes for the Ψ. Indicate where the probability of finding
the electrons is zero for the Ψ2.
nodes
H
a)
H
H
C
O
C - sp3 A.O.
O - sp3 A.O.
H
H
Ψ∗ for the C-O bond
b)
H3C
C
N
zero probability
Ψ2 for one of the C-N π M.O.s
C - p A.O.
N - p A.O.