CHM 253L Organic Chemistry Laboratory I
Laboratory Follow-Up Assignment #9
Due: Friday, December 10, 2004 by 5:00 pm
Part 1
You should have two NMRs that were handed out for the “competitive nucleophiles” part of the
experiment (you only received the data, but did not actually perform this experiment). The
following information should be turned in for this part of the experiment:
1. Identify the important peaks in each 1H-NMR spectrum and their integral values that will be
needed to determine the relative percentage of each alkyl halide in your mixture.
2. Show the calculations for the percentages of each alkyl halide in both mixtures.
3. Identify the stronger nucleophile in both reactions and provide a brief explanation as to how
you came to this conclusion. You may want to consult sections 6.5 and 7.4 of the Jones text.
4. For which reaction is the difference in nucleophilic strength more important? Explain, in
detail, why your results do or do not make sense according to what you know about the SN2
and SN1 reactions.
Part 2
The second part of this experiment involves an investigation of the kinetics. The following
information should be turned in for this part of the experiment:
1. Write a balanced SN1 chemical equation between each halide and the nucleophile(s) in
solution. HINT: be careful -- you need to really think about what are the major species in
solution and their relative concentrations!!!!!
2. Write a balanced SN2 chemical equation for each halide and the nucleophile(s) in solution.
HINT: be careful -- you need to really think about what are the major species in solution and
their relative concentrations!!!!!
3. Write a balanced E1 chemical equation for each halide and the base(s) in solution. HINT: be
careful -- you need to really think about what are the major species in solution and their
relative concentrations!!!!!
4. Write a balanced E2 chemical equation for each halide and the base(s) in solution. HINT: be
careful -- you need to really think about what are the major species in solution and their
relative concentrations!!!!!
5. Use the data in the table below (compiled class data) to create a series of bar graphs
(EXCEL) to show any trends you have discovered between either: different alkyl halides in
same solvent or same alkyl halides in different solvents (a total of 6 graphs).
Flask #1 = < 1 sec
Alkyl Halide
2-chloro-2-methylpropane
2-bromo-2-methylpropane
2-iodo-2-methylpropane
2-chloro-2-methylbutane
Acetone-water
Flask #2- 840 sec
Flask #3- 230 sec
Flask #4- 65 sec
Flask #5- 17 sec
Flask #2- 12.06 sec
Flask #3- 5.33 sec
Flask #4- 2.52 sec
Flask #5- 1.72 sec
Flask #2- 2 sec
Flask #3- 2 sec
Flask #4- 2 sec
Flask #5- 2 sec
Flask #2- 525 sec
Flask #3- 113 sec
Flask #4- 40 sec
Flask #5- 21 sec
2-Propanol-water
Flask #2- 479 sec
Flask #3- 107 sec
Flask #4- 37.4 sec
Flask #5- 15.6 sec
Flask #2- 18.8 sec
Flask #3- 9.42 sec
Flask #4- 1.84 sec
Flask #5- 1.01 sec
Flask #2- 14.22 sec
Flask #3- 4.00 sec
Flask #4- 2.84 sec
Flask #5- 1.94 sec
Flask #2- 451 sec
Flask #3- 119 sec
Flask #4- 35 sec
Flask #5- 20 sec
6. Compare/contrast the graphs (What do the graphs indicate or suggest?) that you generated in
question #5. In particular, you should consider the following situations:
a. Using a different set of alkyl halides (e.g. 2-chloro-2-methylpropane and 2bromo-2-methyl-propane) in the same solvent system.
b. Using the same alkyl halide (e.g. either 2-chloro-2-methylpropane or 2-chloro-2methylbutane) in the two different solvent systems.
7. Using sound chemical theory/logic, describe the reasons for any differences among the data
sets in question #6.
Individual data (choose ONE of the two sets that you performed):
8. Was there a chemical reaction in Flask #1? How do you know? If there was a chemical
reaction in Flask #1 describe the reaction by means of a balanced chemical equation.
9. Was there a chemical reaction in Flasks #2-#5? How do you know?
10. If there were chemical reactions in Flasks #2-#5, what observations did you make about the
similarities and differences in each reaction? Using sound chemical theory/logic, describe the
reasons for the differences and similarities between the reactions in Flasks #2-#5. I am
asking you here to think like the molecules in the flask. What types of intermolecular forces
are occurring in each case? Again, I think it would be helpful to consult Jones sections 6.5
and 7.4.
11. What mechanism (from the menu of possibilities from questions #1-4) best explains the
results? Why?
12. Is an additional experiment needed to verify the mechanism? If so, describe it and what
information the experiment would provide.
13. How might the results of the experiment been different if the substrate was 2-fluoro-2methyl-propane?
14. How might the results of the experiment been different if the solvent system was changed to
methanol-water?
Conclusions:
15. In conclusion, what statement(s) can you make about the role of solvent in this experiment?
16. What statement(s) can you make about the role of the halogen in this experiment?
Collateral Assignment
Complete Experiment #6.6 (SN1 Reaction of Alkyl Halides and Water) from the “Molecular
Modeling Workbook for Organic Chemistry”
Laboratory Follow-Up Assignment #1
Due: Friday, January 23, 2004 by 5:00 pm
Part 1
You should have two NMRs that were handed out for the “competitive nucleophiles” part
of the experiment (you only received the data, but did not actually perform this
experiment). The following information should be turned in for this part of the
experiment:
1. Identify the important peaks and their integral values that will be needed to determine
the relative percentage of each alkyl halide in your mixture.
2. Show the calculations for the percentages of each alkyl halide in both mixtures.
3. Identify the stronger nucleophile in both reactions and provide a brief explanation as
to how you came to this conclusion. You may want to consult section 6.7d of the
Jones text.
4. For which reaction is the difference in nucleophilic strength more important?
Explain, in detail, why your results do or do not make sense according to what you
know about the SN2 and SN1 reactions.
Part 2
The second part of this experiment involves an investigation of the kinetics. The
following information should be turned in for this part of the experiment:
1.
Prepare
two
EXCEL
plots
as
follows:
(a) ln(infinity titer – titer at each time t) versus time -- as determined by subtracting
the volumes at each time from the infinity volume and then using M1V1=M2V2 to
convert to the molarity of HCl -- this graph represents the 1st order ln[ ] vs. time
relationship
(b) 1/(infinity titer – titer at each time t) versus time -- as determined by subtracting
the volumes at each time from the infinity volume and then using M1V1=M2V2 to
convert to the molarity of HCl -- this graph represents the 2nd order 1/[ ] vs. time
relationship
(c) Determine the best fit (trendline) line through the data and determine the equation
for
the
line
with
slope
and
R2
value.
(d)
Determine
the
value
of
the
rate
constant
(k).
(e) Write the rate law for this reaction (kinetics equation, e.g. rate = k[x][y]).
(f) According to your graphs, is the reaction a first or second-order process? Provide a
short narrative description of the results of this experiment and discuss whether your
experimental data is consistent or not with the rate law. You will also want to discuss
any potential contributions of error that enable the data to skew from expected results.
(g) Provide a complete reaction mechanism that is consistent with your determined
process (either SN1 or SN2).
2. Why did we add H2O to the infinity titer?
3. Why do we use a water/isopropanol solvent mixture instead of pur water? You may
want to provide a reaction energy diagram that demonstrates the difference between
using pure water and the mixture.
4. How does acetone slow down the reaction rate? Explain. You may want to provide a
reaction energy diagram that demonstrates the change caused by the acetone.
5. Why does the solution after titration return to the yellow color when it is left to sit for
some time on the laboratory bench?
Collateral Assignment
Complete Experiment #6.6 (SN1 Reaction of Alkyl Halides and Water) from the
“Molecular Modeling Workbook for Organic Chemistry”