Name:_____________
Chemistry 114
First Hour Exam
Remember- Show all work for partial credit
1. (15 points) Hot and spicy food contain molecules that stimulate pain detecting nerve
endings piperine (below) is one such compound found in black and white pepper.
a. Complete the above Lewis Structure by showing all lone pairs of electrons
There should be 2 lone pairs on each oxygen and 1 lone pair on the N
b. How many carbon atoms are sp, sp2, and sp3 hybridized in this molecule?
sp=0 sp2 =11 sp3 = 6
c. What is the hybridization of the N in the above structure?
sp3
d. Give the approximate values for the bond angles 1-6
1 120
2 120
3 120
4 120
5 109
6 109
2
2. (15 points) Using the molecular orbital model to describe the bonding in F2+, F2, F2and F2-2, predict the bond orders and relative bond lengths for these four species.
Which ones are paramagnetic?
F*2p
B*2p
B 2p
F 2p
F* 2s
F 2s
F2+
989
9898
98
89
89
Magnetism
Para
Bond Order
(8-5)/2=3/2
Bond length
Shortest
F2
F2-
F2-2
9898
9898
98
98
98
8
9898
9898
98
98
98
89
9898
9898
98
98
98
Dia
Para
Dia
(8-6)/2=1
(8-7)/2=1/2
(8-8)/2=0 Unstable
Medium
Longest
N.A.
3. A (5 points) What is the difference between a F bond and a B bond?
A F bond has its electron density along the line connecting the two bonded
atoms, a B bond has its electron density to either side of the line connecting the atoms.
B (5 points) When you hybridize s atomic orbitals you can only make F type molecular
orbital. When you hybridize p atomic orbitals you can make either F or B type
molecular orbitals, why?
Because s orbitals are spherically symmetric, when you hybridize two s orbitals
together the resulting electron density is always along the line connecting the atoms
and is hence a F bond. P orbitals are bi-lobed shape arranged along the three principal
axes. When a bond is formed from two p orbitals aligned along the line connecting the
atoms, you get electron density along the line connecting the atoms and a F type bond.
When a bond is formed from the orbitals that are not on this line, the electron density is
to either side of the line connecting the atoms, and you get two different B bonds. A
diagram shows this more easily than words
4. (10 points) What is paramagnetism?, diamagnetism? What determines if a molecule
is paramagnetic or diamagnetic?
Paramagnetism is when a compound is attracted to an external magnetic field,
diamagnetism is when a compound is repelled by an external magnetic field. A
molecule is paramagnetic when it contains unpaired electrons, and it is diamagnetic
when all of its electrons are paired.
3
5. (15 points) Draw the structures of the compounds named below. Some of these
names are wrong. When you find one of these incorrectly named compounds, give the
proper name for the chemical.
A. 2,3-diethylheptane
B. 2-cycloheptene
4-ethyl-3-methyloctane
1-cycloheptane or
Cyclohepatane
C. 3-chloro-2-octanol
D. 4-methyl-1-ethylcyclopentene
Name is OK as written
1-ethyl-4-methylcyclopentane
E. p-dinitrobenzene
.
1,4-dinitrobenzene
6. (10 points) Identify as many functional groups as you can on the following two
compounds. Do any of these compounds have acid or base properties?
4
Pyridoxine
(Vitamin B6)8
Thiamine (Vitamin B1)6
All OH’s are alcohols
All N’s are amines
Each structure has at least 1 aromatic ring
The S in Thiamine is a sulfide but that is a freebie since we didn’t have that group in
class
Both structures can be considered bases because they contain amines
7. (10 points) What does the term catalytic reforming refer to?
Catalytic reforming is one of the processes used in the petroleum industry in the
refining of crude oil. It is a process in which small, nonaromatic compounds are
reformed into larger aromatic compounds. These aromatic compounds raise the
octane of gasoline making it a more profitable product.
8. (5 points) When toluene (C 6H5CH3) reacts with chlorine gas in the presence of
iron(III) catalyst, the product is a mixture of ortho and para isomers of C6H4ClCH3.
However, when the reaction is light-catalyzed, with no Fe3+ catalyst present, the product
is C6H5CH2Cl. Explain.
The reaction of Cl 2 with an iron catalyst is a typical substitution reaction involving an
aromatic compound. The reaction of Cl 2 with light is a typical substitution reaction
involving an unsaturated hydrocarbon. Thus the Fe catalyzed reaction reacts with the
aromatic part of the toluene molecule, while the light reaction involves the aliphatic part
of the molecule.
9. (5 points) Kevlar, used in making bullet proof vests, is made by the condensation
copolymerization of the monomers
5
Draw the
structure of the Kevlar chain
10. (5 points) Viscosity is a measure of how ‘thick’ a solution is. If it has low viscosity, it
is thin and runny, if it has high viscosity it is thick and tends to coat objects. The
viscosity of oil in a motor is very important in keeping an engine running. If the viscosity
is too low, the oil doesn’t coat the hot metal parts, and the valves and cylinders get to
hot and weld themselves together. If it is too viscous, the oil is thick and syrupy, and
the parts of the engin can’t move (like when you try to start your engin when its -20).
Poly(lauryl methacrylate) is used as an additive in motor oils to counter the loss of
viscosity at high temperature. The structure is
The long chain hydrocarbon of poly(lauryl methacrylate) make the polymer soluble in oil
(a mixture of hydrocarbons with mostly 12 or more carbons) At low temperature the
polymer is coiled into balls. At higher temperature the balls uncoil and the polymer
exists as long chains. Explain how this helps control the viscosity of oil.
At low temperature the polymer is coiled up so it has little interaction with the rest of the
oil and it’s viscosity is low. At high temp, where the oil itself starts to lose its viscosity,
this polymer uncoils, and now begins to interact with the oil. In the long, uncoiled form
this has a higher viscosity, so it serves to ‘replace’ the viscosity lost by the rest of the
oil.