Chem 321
Name_ __KEY__________________
Sept 23, 2009
Hour Exam 1, McMurry 7th Ed Chap 1-4
Note: This key combines the answers from FOUR versions of the test. Questions 1-5
and 9 contained only one part in student exams.
1. (15 pts) Write the correct IUPAC names for both of the following compounds:
H3C
H3C
CH3
CH3
CH3
CH3
CH3
1-t-butyl-1-methylcyclopentane
1-isopropyl-1-methylcyclopentane
2,2,3,3-tetramethylheptane
H3C
CH3
CH3
2. (10 pts) Draw a structural formula for
cis-1-methyl-2-(2-methylbutyl)cyclobutane.
trans-1-ethyl-3-(2-methylbutyl)cyclobutane
cis-1-ethyl-3-(2-methylbutyl)cyclobutane
CH3
H3C
CH3
CH3
H3C
CH3
3. (10 pts) The following substances can act as Bronsted acids with the corresponding pKa's
shown.
8.5
Nitroethane CH3CH2NO2
Ammonium ion NH4+
9.3
Water OH2
15.7
Ammonia NH3
32
Benzene C6H6
41
(a) Which of these acids is the strongest (weakest)?___Nitroethane (benzene)_________.
(b) Which acid of these would have the strongest (weakest) conjugate base__ Benzene
(Nitroethane) _?
(c) Write a balanced chemical equation for a reaction between hydrogen sulfide nitroethane and
the conjugate base of benzene (ammonia) propene. Tell whether this reaction will proceed as
written, or not.
CH3CH2NO2
+ C6H5-
CH3CH2NO2
+ NH2-
CH3CHNO2CH3CHNO2-
+ C6H6
+ NH3
4. (22 pts) Consider the two chair conformations of the following compound:
a. Draw structural formulas for both chair conformations of this compound. Show all axial
hydrogens in each.
b. List all applicable steric interactions for each one
CH3
CH3
Cl
Cl
H
CH3
H
H
H
H
H
H
Cl
H
H
H
Cl
(2) H-methyl 1,3
diaxial inter
(2 ) H-Cl 1,3 diaxial
interactions
(2 ) H-Cl 1,3 diaxial
interactions
(2) H-methyl 1,3
diaxial inter
H
H
H
CH3
H
CH3
H
Cl
H
H
H
H
H
H
CH3
H
H
Cl
H
Cl-methyl gauche
interation
H3C
H3C
CH3
CH3
Cl
H
H3C
CH3
CH3
H
H
H
Cl
(2) H-methyl 1,3
diaxial inter
(2 ) H-Cl 1,3 diaxial
interactions
H
H
CH3
Cl
H
(2) H-methyl 1,3 diaxial
inter
Cl-methyl gauche
interation
Cl
CH3
H
H
H
H
CH3
H
H
H3C
H
H
H
H
H
H
Cl
(2) H-methyl 1,3
diaxial inter
(1) methyl-methyl 1,3
diaxial inter
(2 ) H-Cl 1,3 diaxial
interactions
CH3
H
Cl
H
Cl-methyl gauche
interation
c. Tell which conformation is more stable, and why you chose it.
(See equilibrium arrow directions.) The more stable conformations have fewer steric interactions.
Quantitatively, the sum of the “energy penalties” for all the steric interactions of the less stable
conformation is greater than this sum for the more stable conformation.
In the case where the number of steric interactions are the same in the two conformations, the
H-methyl 1,3-diaxial interaction energy is greater than the H-Cl 1,3-diaxial interaction energy.
1
H
5. (7 pts) Which would have the larger dipole moment, chlorocyclobutane or 1,1dichlorocyclobutane (1,1,3,3-tetrachlorocyclobutane, or 1,1,2,2-tetrachlorocyclobutane; cis or
trans-1,3-dichlorocyclobutane)? Defend your choice using (some kind of) diagram.
Cl
Cl
Cl
H
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
PM3
1.45 D
semi-empirical
1.62 D
1.87 D
Cl
H
Cl
H
Cl
H
Cl
0
H
1.98 D
0
The vertical components of the two Cl’s in 1,1-dichlorocyclobutane cancel, but the horizontal
components (i.e. those in the plane of the ring) add up to more than a single C-Cl dipole. The
isomers contain Cl’s oriented in opposite directions have zero dipole moments.
6. (6 pts) The molecule below contains H, C (gray), and O (red) atoms. What is the transparent
surface surrounding the model? What do the blue and red colors represent?.
The surface itself outlines the probability of finding all the electrons of the
molecule greater than a certain electron density. (This one is about 0.03
electrons per Å3.) The colors “painted” on the surface reflect the electrostatic
potential at each point, with red showing concentration of negative charge,
and blue showing concentration of positive charge. The positive charge
originates in the nuclear charge not being neutralized because the surrounding
electrons have been pulled elsewhere. The official name for this kind of
surface is “electrostatic potential 3D mapped isosurface”.
7. (9 pts) In the following molecular model, indicate the positions of the multiple bonds and
identify three functional groups: (C , gray; N, blue; O, red)
Amine
Carboxylic acid
Arene
Hydroxyl (alcohol)
Amine
Carboxylic acid
O
H
H
O
NH2
Alkyne
O
O
H
Arene
H
O
C
H
NH2
CH
2
8. (12 pts) In the above molecule,
sp -hybridized carbons ....... 0
sp2-hybridized carbons ...... 7
sp3-hybridized carbons ...... 1
non-bonding electron pairs... 7
how many of each of the following are there?
2
7
1
5
9. (10 pts) Draw Lewis structures (using lines for bonds), including all non-bonding electrons and
non-zero formal charges, of the following resonance stabilized ion:
C2O42-
O
C3H3O3-
H
O
C
C
O
H
O
O
C
C
C
O
O
O
C
C
O
H
O
O
C
C
C
H
O
-
H
O
O
O
O
C
C
O
O
C
C
N
H
H
O
O
H
H
H
C2H2NO2-
C2H2NO2
O
H
O
O
C
C
C
O
C
C
O
O
O
O
C
C
O
O
H
O
O
C
C
N
H
H
O
O
C
C
H
H
H
N
N
N
O
C
O
C
O
C
O
C
O
C
O
C
H
O
H
N
H
H
3