Lab- Hydrocarbons
PSI Chemistry
Name_________________
Purpose: To investigate the three dimensional shapes of hydrocarbon molecules
by building molecular models.
Procedure
As you construct each model, complete Data Tables 2a and 2b. Answer each
question on another piece of paper or next to each question.
Part A. Continuous-Chain and Branch-Chain Alkanes
1. Make a model of methane, CH4. Are all the angles formed by any two C—H
bonds the same?
2. Make a model of ethane, C2H6. Can you hold one carbon and its attached
hydrogens in a fixed position and rotate the other carbon and its attached
hydrogens, without breaking the C—C bond?
3. Make a model of propane, C3H8. Can this model be rearranged to make a
different molecule?
4. Make a model of butane, C4H10. Can this molecule be rearranged to form a
new molecule that has the same molecular formula but a different structural
formula? If so, name the structure. Molecules that have a same formula but
different structure are called Structural Isomers.
5. Make a model of pentane, C5H12. Construct as many structural isomers as
you could. For each isomer, give a name for each and sketch each in Data
table 2a.
Part B. Cycloalkanes
6. Construct a model of hexane, C6H14. Manipulate the structure so that you
form a ring. You will have to remove two hydrogens to join the ring. The
structure is called cyclohexane.
Manipulate your cyclohexane molecule so that two carbons directly across
the ring from each other are above the plane of the other four. This is called
the boat conformation. Now manipulate the molecule so that one carbon is
above while the other is below the plane of the other four carbons. This is the
chair conformation. In Data Table 2a, draw these two conformations.
Is there free rotation about the C—C bond in cyclohexane?
Part C. Alkenes and Geometric Isomers
7. Make a model of ethane, C2H4. Can you rotate the carbons about the double
bond?
8. Remove one hydrogen from each side and replace them with chlorine. The
name of the resulting compound is 1,2-dichloroethene, C2H2Cl2. There are
two structures possible for this compound. They are called geometric
isomers, and are distinguished by the prefix cis and trans added to the name.
Construct both geometric isomers.
9. Make a model of butene, C4H8. This compound has two structural isomers.
Name these isomers and, in Data Table 2b, give their molecular and
structural formulas. Are there also geometric isomers for butene?
Part D. Alkynes and Arenes
10. Make a model of ethyne, C2H2. In Data Table 2b, describe the shape of the
molecule. Can you rotate the molecule about the triple bond?
11. Make a model of benzene, C6H6, using alternating double and single bonds to
approximate the aromatic bonds. Do all the atoms lie in the same plane?
Can benzene exist in the boat and chair conformations?
Data Table 2a
Methane
Molecular Formula_____
Structual Formula:
Sketch:
Ethane
Molecular Formula_____
Structual Formula:
Sketch:
H—C—H angle?___________________
Rotation about C—C bond?___________
Propane
Molecular Formula_____
Structual Formula:
Sketch:
Butane
Molecular Formula_____
Structual Formula:
Sketch:
Other Isomers?___________________
Pentane
Molecular Formula_____
Structual Formula:
Sketch:
Cyclohexane Molecular Formula_____
Structual Formula:
Sketch:
Rotation about C—C bond?___________
Data Table 2b
Ethene
Molecular Formula_____ 1,2-dichloroethene
Structual Formula:
Molecular Formula_____
Sketch:
Structual Formula:
Sketch:
Rotation about C—C bond ?__________
Butene
Molecular Formula_____ Ethyne
Molecular Formula_____
Structual Formula:
Structual Formula:
Structural Isomers:
Sketch:
Sketch:
Shape?___________________________
Rotation about triple bond?___________
Geometric Isomers:
Sketch:
Benzene
Molecular Formula_____
Structual Formula:
Sketch:
Is the molecular planar?______________
Boat and Chair conformatioms?_______