ORGANIC CHEMISTRY I LAB
WORK-SHOP 1
Week 4
I. Alkanes: Structures and Models
1.
Write the names and structures of straight chain alkanes from C1 to C10
2.
Construct butane using models
2.1.
Identify all primary (1o), secondary (2o), and tertiary (3o) carbons
(if any)
2.2.
Place a methyl group on one of the secondary carbons. Draw the
structure. Name the structure.
2.3.
Place a methyl group on the other secondary carbon. Name the
structure. Discuss with your group members whether the name of
the new molecule should be different (review the naming rules)
2.4.
If the names of the structures in 2.2 and 2.3 are the same, what is
the relationship between the two secondary carbons?
3.
Each group should build one of the structures below using models (no need to
place any hydrogens on carbons)
C
C
C
C-C-C-C-C-C-C-C
C
C CC
C-C-C-C-C-C
C
(1)
3.1.
3.2.
3.3.
3.4.
C
C
C
C
C-C-C-C-C
C
C-C-C-C
(2)
(3)
Name your group’s molecule assuming that all missing bonds are
hydrogens.
Compare the name of your structure with those of the other groups.
After confirming the name of each structure, compare your
structures as well. Write a short paragraph summarizing your
conclusion
Under what conditions would the three structures be different?
(refer to question 3.5 before answering question 3.4)
3.5.
Are the structures on
the right different
from each other?
If so, when are they
different?
4.
Give a definition for the term conformation
4.1.
Can “conformational isomers” be isolated from one another?
4.2.
Build a model for ethane as in question 3.5
4.3.
How many conformational isomers of ethane are there?
4.4.
Draw the two “extreme” conformations of ethane in 3.5 using
Newman Projection Representations
4.5.
Give a definition of a dihedral angle as it applies to ethane
4.6.
What is the dihedral angle in the staggered conformation of ethane
4.7.
What is the dihedral angle in the eclipsed conformation of ethane
5.
Construct a model of propane (similar to the models in 3.5, but substitute one
of the white balls (H atom) with a methyl group
5.1.
Make a model of the eclipsed conformation. Draw its Newman
Projection Representation
5.2.
Make a model of the staggered conformation. Draw its Newman
Projection Representation
6.
Draw an energy diagram (similar to that given in the text), and draw the
correct conformations (in Newman Projection Representation) of ethane in the
minima and maxima points of the graph.
7.
Construct a model of 1,2-dibromoethane.
7.1.
Make a model of the eclipsed conformation (note that there will be
two eclipsed conformations, one of which will be less stable than
the other). Draw their Newman Projection Representations.
7.2.
Make a model of the staggered conformation (note that there will
be two staggered conformations, one of which will be less stable
than the other). Draw their Newman Projection Representations.
Identify the names given to the two different staggered
conformations.
7.3.
Construct an energy diagram similar to the one for question and
draw the correct conformations (in Newman Projection
Representation) of 1,2-dibromoethane in the minima and maxima
points of the graph.
8.
Construct a model of butane and follow the directions as in 7.1 to 7.3. When
you draw a Newman Projection Representation for butane, assume as if you
are working with ethane (refer to question 3.5); except that replace one
hydrogen on each carbon with a –CH3 group.
9.
Draw ethane below in “zig-zag” form (in skeletal structures); however, show
all hydrogens in “dashed” and “wedged” forms to illustrate the distinguishing
aspects of the eclipsed and staggered conformations.
10.
The type of representation you have drawn for question 9 is referred to as
“saw-horse”. Show “saw-horse” representations of
10.1. Gauche conformation of butane
10.2. Anti conformation of 1,2-dibromoethane
10.3. The less unstable eclipsed conformation of butane