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Chemistry 241
Clark College
Homework 2 SOLUTION
Please put your answers on a separate sheet of paper.
Due Thursday, October 2, 2008, IN CLASS.
1. Complete the following Lewis structures by filling in missing electrons (as lone pairs and
bonds), computing formal charges, and indicating equivalent resonance structures, where
they exist. The number of resonance structures that can be drawn is indicated next to the
structure. For each set of structures, please indicate if one resonance structure is better
than the other(s), based on the placement of the formal charges.
a) CH3 – N – N – N (2 resonance structures)
b) CH3 – C – N – O (2 resonance structures)
c) [S – C – N]-1 (2 resonance structures)
**Note: there are more structures that can be drawn that do not violate the octet rule. However,
these have larger formal charges, and were eliminated for that reason!**
a)
H
H C N N N
H
b)
H
H C C N O
H
c)
H
H C N N N
H
Both compounds have similar stabilities based on formal
charge. Reactivity of the molecule indicates that the second
is very reactive, so the first is more stable. In addition,
electronegativity actually increases as the s-character
increases (with hybridization changes).
H
H C C N O
H
S C N
S C N
The second structure is more stable, as it puts the
negative charge on the more electronegative element.
Putting the negative charge on the sulfur
is preferred, so the first structure is
preferred.
2. Explain the following observations. In your explanation, draw the complete Lewis structures
for both carbonic acid and the carbonate ion, and use the structures to justify your
explanation.
• For carbonic acid, the C–O bond length is 134 pm, and the C=O bond length is 121 pm.
• For carbonate ion, all C–O bond lengths are 127 pm.
Data obtained from: March, J., Advanced Organic Chemistry; 4th ed.; Wiley; New York; 1992; p.
21.
O
H
O
C
O
H
With the hydrogens in place, all C-O bonds
are locked in place, giving isolated bonds.
O
O
C
O
O
O
O
C
O
O
C
O
Without the hydrogens, the double bond resonates between the carbon and
the three oxygens. This results in bonds that have a bond order of 1.33, and
this is reflected in the bond length, between that of a double and a single.
Fall 2008
Homework 2
Page 1 of 4
Chemistry 241
Clark College
3. Give the molecular formula for each molecule below. Give the hybridization and the
electronic and molecular geometry for the highlighted atoms in the following structures.
OH
a)
b)
C
c)
N
O
O
C6H10O
sp , trigonal planar for
both electronic and
molecular geometries
2
C6H13NO
sp3, tetrahedral,
trigonal
pyramidal, or
“umbrella”
C8H14O
sp3, tetrahedral, bent
4. Draw the Lewis structure for acetonitrile, CH3CN. For the carbon and nitrogen of the nitrile
(CN) group, give the hybridization of the atoms, and draw pictures of the bonding orbitals
used by the two atoms (similar to what we did in class for formaldehyde, CH2O).
sigma orbitals:
H
H
C
C
C
N
H
N
pi orbitals:
sp
C
N
5. Give the molecular formula for each molecule below.
H
O
N
OH
O
O
Cl
Cl
The first molecule is Zoloft ®, and has the formula C17H17Cl2N.
The second molecule is aspirin (acetylsalicylic acid), and has the formula C9H8O4.
Fall 2008
Homework 2
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Chemistry 241
Clark College
6. Consider the structure of Tamiflu® below. Provide the hybridization for the indicated atoms
and list the functional groups that are present in the molecule. Place your answers in the
boxes provided.
sp3
O
Functional Groups Present:
Alkene
Ester
Ether
Amine
Amide
O
sp2
O
NH2
N
O
sp3
H
sp2
7. Give IUPAC names for the following compounds.
Cl
a)
b)
c)
F
d)
Br
a)
b)
c)
d)
3-bromo-2-methylpentane
1-ethyl-1,2-dimethylcyclopentane
2-chloro-3-ethylheptane
3-ethyl-4-fluoro-2-methylhexane  preference in naming is given to numbering the chain
with the most substituents, and having the substituents at the lowest total set of
numbers. You can get these numbers if you number down the ‘side chain’
3-fluoro-4-isopropylhexane was also accepted.
Fall 2008
Homework 2
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Chemistry 241
Clark College
8. Draw structures for the following compounds.
a) 4-tert-butyloctane
b) 2,2-dichloro-3,4-dimethylhexane
c) 4-ethyl-1,2-cylcohexanediol
d) 5-isopropyl-2-heptene
Fall 2008
Homework 2
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