Homework 1
Organic Chemistry MCAT Review
Summer 2012
Brent Iverson
1
Where are the electrons
1. The most important question in chemistry is: _________________________________________?
valence
2. Atoms prefer a filled ____________________
shell of electrons. The vast majority of stable
bonding in molecules takes place in such a way that this is accomplished.
4 bonds and has ____
0 nonbonded pairs of electrons.
3. Neutral carbon takes part in ____
3 bonds and has ____
1 nonbonded pairs of electrons.
4. Neutral nitrogen takes part in ____
5. If a carbon atom in a molecule has three bonds and one nonbonded pair of electrons around it
OR if an oxygen atom has one bond and three nonbonded pairs of electrons around it, either
-1 formal charge.
atom will have a ____
6. When two atoms of different electronegativity form a covalent bond, the majority of shared electron
more
density is found around the ____________
electronegative atom.
7. For the following molecular formulas, draw complete Lewis line structures in which all atoms
(even H atoms) are drawn, lines are used as bonds, and all lone pairs and formal charges are drawn.
A)
(CH3)3CCH2CH2CO2H
H
H
B)
H H
C
H H
H
C
C
C
C
H H
C
H
H H
H
H2CCHCH2CHCH2
O
C
O
H
C)
CH3OCH2CH2NH3
H
H
H
C
H
H
C
C C
C
H
H
H
H
H
C
H
O
H
H
H
C
C
N
H
H
H
H
2
D. CH3CH2CH3
H
H
H
H
C
C
C
H
H
H
E. (CH3)2CHCH3
H
H
C
H
C
C
H
H
H
H
H H
C
H
F. CH2CHCHCH2
H
C
H
H
H
H
C
C
C
H
H
G. CH3NO2
H
H
O
N
C
O
H
8. Some of the molecules shown below have formal charges. For those that do, write the correct formal
charge next to the appropriate atom. IN ADDITION, SOME OF THE ATOMS ON THESE
MOLECULES NEED LONE PAIRS ADDED. ADD ALL VALENCE LONE PAIRS OF ELECTRONS
WHERE APPROPRIATE.
H
H
H
H
C
N
C
H
H
H
H
B
H
H
C
C
H
H
H
H
H
F
F
H
C
C
F
H
H
O
O
H
H
H
O
C
OH
3
9. For the following molecules, write the hybridization state of each atom indicated by the arrow.
sp2
N
sp2
sp3
sp
sp3
sp2
sp3
O
sp2
sp2
O
MSG
O
O
O
Na
sp2
H
C
H
Nicotine
H
H
C
C
C
H
sp2
sp3
H
H
C
C
C
C
H
C
H
sp3
sp3
H
H
H
H N H
C
C
C
C
H
H
H
H
sp2
H
H
H
Amphetamine
C
H
C
H
C
H
H
sp2
sp2
sp2
H
H
H
C
O
sp3
sp2
sp3
CH3
N
sp2
H
N
sp2
C
H
sp2
H
O
sp2
H
H
sp3
sp2
H
N
H
sp3
O
N
O
sp2
H
C
H
C
C
H
H
sp2
4
10. Describe each bond indicated with an arrow as the overlap of orbitals. For example, an
answer might be
σ Csp -Csp .
3
3
π C2p-C2p
π C2p-C2p
H
C
H
σ Csp-H1s
C
C
σ Csp -H1s
H
3
σ Csp-Csp
H
σ Csp -Csp
3
σ Csp -Csp
σ Csp -H1s
2
3
H
H
C
C
H
H
σ Csp -Csp
3
2
2
σ Csp -Csp
2
2
H
C
C
H
O
π C2p-C2p
5
Note this O
atom will
have some sp2
character, but
is mostly sp3.
10. (cont.)
σ Csp -Csp
3
σ Csp -Csp
2
2
3
σ Osp -H1s
CH3
Ibuprofin
3
O
CH3
H
O
H 3C
σ Csp -Csp
3
σ Csp -Osp
π C2p-O2p
2
3
σ Csp -Nsp
2
σ Csp -Csp
2
LSD
H
2
2
2
O
N
N
σ Nsp -Csp
2
3
N
CH3
π C2p-C2p
σ Csp -Csp
2
2
σ Nsp -Csp
2
Methyl
Isocyanate
(the molecule that
cuased the Bhopal
tragedy in India in
1984)
σ Nsp -Csp
3
2
σ Csp-Osp
N
H3C
2
C
O
π N2p-C2p
π C2p-O2p
6
11. The following molecules are best represented as the hybrid of contributing structures. Draw the second
important contributing structure in the space provided, including all lone pairs and formal charges. For
the structure on the left, use arrows to indicate the movement of electrons to give the structure you
drew. Finally, if one of the two contributing structures makes a dominant (major) contribution to the
resonance hybrid, draw a circle around the dominant (major) contributor. You might want to read these
directions again to make sure you know what we want.
A.
H
H
H
O
C
C
H
O
H
C
O
C
O
H
B.
H
H
H
H
C
C
C
H
H
C
C
N
H
N
N
H
H
C
C
N
H
H
C
H
H
D.
C
H
H
C.
H
H
O
C
H
C
H
H
H
C
O
C
C
H
H
H
7
H
H
C
11. (cont.)
O
H
H
C
C
O
H
H
H
H
E.
either of
these are
correct
H
filled valence
H
H
C
O
H
H
C
C
C
O
H
H
C
C
H
H
H
O
H
O
H
F.
H
H
H
H
H
C
O
H
H
C
C
H
H
C
O
H
H
C
C
H
H
H
G.
H
H
H
H
C
C
N
H
H
H.
H
C
C
N
H
filled valence
H
H
O
H
O
C
C
H
H
C
H
filled valence
C
C
H
H
H
C
H
negative charge
on more
electronegative
element
H
8
12. (10 pts each) The following molecules are best represented as the hybrid of three contributing
structures. Draw the second and third important contributing structures in the spaces provided,
including all lone pairs and formal charges. For the two structures on the left in each problem, use
arrows to indicate the movement of electrons to give the structures you drew. There is no need to
draw any circles around any of these contributing strucures. You might want to read these directions
again to make sure you know what we want.
A.
O
O
C
O
O
O
O
C
O
O
C
O
B.
H
O
C
H
H
N
O
C
O
H
N
O
C
H
O
O
O
H
N
O
Ribbit
9
13. Draw a circle around all of the molecules below that can be considered aromatic.
H
N
O
N
N
N
H
N
H
N
H
N
N
N
14. On the left is drawn the Lewis structure of a simple amide. Draw the two next most important
contributing structures in the spaces provided. Be sure to show all lone pairs and formal charges. You do
not need to draw arrows on the structures, but you can if it helps you.
H
H
C
H
H
O
H
C
N
H
H
C
H
H
O
H
C
N
H
H
C
H
O
C
N
H
H
An important feature of an amide bond is that there is a partial double bond between the carbonyl carbon
and nitrogen. For the contributing structures you drew in Problem 2., draw a circle around the one that
predicts this partial double bond.
Notice This
10
15. On the lines provided, state the hybridization state of the atom indicated by the arrow.
sp2
sp2
H
O
H3C
CH3
CH3
N
N
CH3
H
N
sp2
H
H
H
sp2
sp3
sp2
H
N
N
N
sp2
N
sp2
H
16. On the lines provided, state the atomic orbital that contains the lone pair of electrons indicated by
the arrow.
2p
H3C
sp2
H
O
H
CH3
CH3
N
N
CH3
N
H
H
H
2p
sp3
H
sp2
N
N
N
H
2p
N
sp2
11
17. Name the circled functional groups present in the following molecules.
ketone
ether
carboxylic acid
amide
O
O
H
N
O
HO
O
HO
alcohol
imine
acetal
nitrile
N
H3CO
N
O
O
anhydride
O
O
aldehyde
O
H
12
17 (cont.) The drug Etoposide is a chemotherapeutic agent that has been used against a number of cancers
over the years. It operates by inhibiting an enzyme called topoisomerase that is required for DNA
replication. Cancer cells need to replicate faster than normal cells, so drugs like Etoposide can be used to kill
cancer selectively. Look at Etoposide and identify the three acetals and one lactone.
Acetal
H
H3C
Acetal
O
O
HO
O
O
OH
H
O
O
O
Acetal
H
O
Etoposide
H3CO
Lactone
(an ester)
OCH3
OH
13
18. On the line provided, write IUPAC names for the following molecules.
CH3
H3C
CH3
CH
CH2
1
4
3
2
5
7
6
9
8
10
H3C CH2 C CH2 CH2 CH CH2 CH2 CH2 CH3
CH2
CH3
3,3-diethyl-6-isopropyldecane
or 3,3-diethyl-6-(1-methylethyl)decane
3
2
7
5
4
6
9
8
10
1
6-sec-butyl-2,2-dimethyldecane
or 2,2-dimethyl-6-(1-methylpropyl)decane
9 CH3
1
8 CH2
7
CH3 C
CH3
6
CH3
CH3 2 CH3
CH
5
CH2 CH
4
CH
3
CH
CH3
CH3
2,3,4,5,7,7-hexamethylnonane
14
18. (cont.)
I
COOH
(3R,4S,6R)-4-Iodo-3,6-dimethyloctanoic acid
O
H3C
O
N
CH3
CH3
N,N-Dimethyl-3-oxopentanamide
19. In the space provided, draw the following molecule:
Cis-Diisopropyl cyclopentane-1,3-dicarboxylate
O
O
O
O
15
20. For the following acid base reactions, circle the side of the equation that predominates at equilibrium.
In each case identify the stronger and weaker acids by comparing relative stabilities
of the anions which are the conjugate bases of the two acids. Equilibrium favors
formation of the weaker acid. You will notice this means you circled the side with
the more stable anion.
OH
O
+
+
O
O
O
resonance
stabilized anion
OH
NH 2
+
oxygen is more
electronegative O
than nitrogen
H-I +
H
OH
Cl
N
+
O H
NH
+
H
H-Cl +
H
Iodine is a larger
anion than
chloride
I
H
+
O
H
F
F
C
F
+
C
Cl
OH
C
Cl
F
O
F
C
O
C
F
Cl
O
+
C
Cl
C
O
Cl
H H
pKa = 20
H2C
S
O
C
OH
O
O
+
H
H
Cl
O
N
+
CH3
O
H
H3C
S
CH3
O
pKa = 23
16
21. Rank the following from 1 to 4 with respect to relative anion stability, with a 1 under the most stable
anion and a 4 under the least stable anion.
O
O
H
Inductive effects
H
F
O
H
Cl
4
O
Cl
O
H
O
O
H
Cl
3
O
H
F
2
F
1
22. Rank the following from 1 to 4 with respect to relative acidity, with a 1 under the most acidic and a 4
under the least acidic molecule.
O
Inductive effects
O
H
H
F
OH
H
Cl
4
O
Cl
OH
H
O
OH
H
Cl
3
OH
H
F
2
F
1
23. At pH 7.0 in water, circle the species that will be predominant for the amino acid alanine.
H3C
NH2
H3C
NH
C
C
O
H
NH2
C
OH
OH
NH3
H3C
O
H
O
H
O
OH
H3C
C
O
H3C
NH3
H3C
C
O
H
O
At pH 7, the amine is
protonated and the carboxylic
acid is deprotonated, as can be
predicted based on the relevant
pKa vaules in Table 4.1. Use
the methylammonium ion pKa
value (10.64) and the acetic
acid pKa value (4.76) as
reference values and compare
those to the pH value of 7.
zwitterion
The species you circled has the special name of ________________________
17
24. Rank the following from 1 to 4 with respect to relative acidity, with a 1 under the most acidic and a 4
under the least acidic molecule.
H2O
CH4
2
NH3
4
HF
3
HBr
4
1
HI
HCl
2
O
H2S
3
1
O
Cl
H3C
OH
OH
2
H3C
1
3
O
H3C
C
C
CH3
4
H
H
H3C
OH
H
H
C
H3C
C
CH3
OH
1
H
2
H
3
4
25. For each molecule, draw a circle around the most acidic H atom. Note there might be more than one
on the same molecule, and you will get it correct if you circle any of the most acidic H atoms.
H
H
C
C
H
H
These two
are just as
acidic
C
H
H
O
C
C
H
H
O
C
O
O
C
C
O
H
H
O
H
O
C
H
H
H
H
Cl
C
C
H
Cl
H
H
N
C
H
H
O
C
O
H
O
C
O
H
18