Experiment 4 – Week 4
11
Name
Experiment 4
Week 4 In-Lab Questions:
How Can a Complex
Alkene be Synthesized?
CH3
R Br
?
R Mg Br
dry ether
solvent
R-MgX
H
R' O
?
H
CH3
CH3-CH
CH3-CH2-CH2-CH2-Br + Mg Þ
?
CH
O
CH-CH2-CH2-CH2 CH
1. dry ether
O
2. H2SO4 H2O
CH3
H
H3PO4
CH3

C
CH-CH2-CH2-CH2
C
CH3
+ H2O
H
Figure 1: Proposed Synthesis of 2-Methyl-2-Heptene
Percent Yield Product:
One indication of the success of a synthesis is the percent yield. It gives an indication of the overall efficiency
of the synthetic procedure and technique of the experimenter. To determine the overall yield for a multistep
synthetic procedure, we need to understand how the individual reaction steps relate to each other. For example:
What is the maximum number of moles of 2-methyl-2-heptene that could be produced by the following
sequence of reactions? First 0.21 mole of 1-bromobutane reacts with 0.20 mole of magnesium turnings. Then
all of the butyl magnesium bromide produced reacts with 0.21 moles of 2-methylpropanal. Finally, all of the
resulting 2-methyl-3-heptanol reacts with 25 mL of 85% phosphoric acid.
 What information must be obtained from Figure 1 to be able to complete the required calculation?

Explain how the information for the equations can be used to determine the maximum number of moles of
2-methyl-2-heptene that could be produced. What is the mass of this number of moles of the product?
Show calculations.

How many moles of 2-methyl-2-heptene would constitute a 75 % yield for the overall synthesis. What is the
mass of this amount of product? Explain the logic you used to determine the answer and show all
calculations used.

If an experimenter obtained 11.2 g of product from the synthesis described above, what would be that
scientist’s % yield for the synthesis?
CHEM 212 Experiment 4
12
Alkene Synthesis

If a 100 % yield was obtained in the first two steps of the synthesis and 75 % yield was obtained in the third
(dehydration) step, what would be the overall % yield for the total synthesis? Explain your reasoning and
show all calculations.

If a 100 % yield was obtained in the first and third steps and a 75 % yield was obtained in the second step,
what would be the overall % yield for the total synthesis? Explain your reasoning and show all calculations.

If a 100 % yield was obtained in the second and third steps and a 75 % yield was obtained in the first step,
what would be the overall % yield for the total synthesis? Explain your reasoning and show all calculations.

If a 100 % yield was obtained in the first step, an 80 % yield was obtained in the second step and a 75 %
yield was obtained in the third step, what would be the overall % yield for the total synthesis? Explain your
reasoning and show all calculations.

If a 90 % yield was obtained in all three steps, what would be the overall % yield for the total synthesis?
Explain your reasoning and show all calculations.
Product Purity:
A second indication of the success of a synthetic procedure is the purity of the final product. Ideally we would
desire to obtain a 100 % pure compound. In our synthesis we are judging product purity from the gas
chromatographic analysis of the final product. In variably any product will contain small amounts of impurities
from starting materials and side products. In our synthesis we know that there is at least one likely additional
alkene product from the dehydration of 2-methyl-3-heptanol. Table 1 in the Experiment 4 Week 3 procedure is
designed to illustrate the various proportions of the components of the isolated product. In the example
provided in the procedure, the product mixture contained 2 products (2-methyl-2-heptene and an unidentified
product) and two other compounds from the starting materials (2-methyl-3-heptanol and 2-methyl-3-heptanone).
So the total of the areas of all of the peaks in the chromatogram (100 %) represents some product (50.%
2-methyl-2-heptene, 25.% unidentified product) and some recovered starting materials (20.% 2-methyl-3heptanol and 5.% 2-methyl-3-heptanone).
 If as indicated above, we isolated 11.2 g of this product mixture, what mass of this sample would consist of
product compounds (2-methyl-2-heptene & unidentified product)?

What is the overall percent yield of the product compounds in the synthesis? Explain and show calculations.

What percent would 2-methyl-2-heptene be of the product compounds isolated?
calculations.

What would be the overall percent yield of 2-methyl-2-heptene for the synthesis? Explain and show
calculations.
Explain and show