-
Complete the inquiry questions in the handout using the procedure in this video
print out the pdf file and fill out the answers, or write answers on separate sheets of papers but CLEARLY indicate the number of the question before each one. Please send pictures of the final product in one pdf file. - Experiment 19: Reactivities of Some Alkyl Halides
Overview
Use this document to record your observations, analyze the results, and reflect on the mechanisms of the
substitution reactions observed in Experiment 19.
Some of the questions in this document will refer to the elementary steps in organic reactions as well
as the reaction types that were taught in general chemistry. You may refer to the lists below.
Table 1. Common elementary steps for organic compounds and inorganic reaction types.
Organic Chemistry Elementary Steps
General Chemistry Reaction Types
• Coordination
• Heterolysis
• Bimolecular nucleophilic substitution
• Bimolecular elimination
• Nucleophilic addition
• Nucleophile elimination
• Electrophilic addition
• Electrophile elimination
• Carbocation Rearrangement
• Proton Transfer
• Precipitation
• Single Replacement
• Double Replacement
• Acid/Base neutralization
• Combustion
• Redox
• Synthesis
• Decomposition
Part A. Sodium Iodide in Acetone
Introduction
1) Before we analyze the data associated with Experiment 19, Part A, let’s be sure that we understand the
chemical reactions being observed. Although we will not be testing alkyl bromide X, shown below, it
would be expected to undergo substitution under the reaction conditions of the experiment.
a. First, X would undergo an “organic chemistry elementary step”. On the figure below, draw the
curved arrows for this step, provide the structures of all products (organic and inorganic) in the
box, and name the elementary step.
b. One of products of step 1 undergoes a reaction type that you considered in general chemistry.
On the figure below, name the type of reaction and provide the identity of the white powder
that would be observed had we studied alkyl halide X in the experiment.
Figure 1. How alkyl bromide X would react under the conditions of Exp. 19, Part A.
a)
b)
NaI
Br
acetone
alkyl bromide X
product(s) of step 1
white precipitate
“organic” chemistry
“general” chemistry
elementary step 1:
reaction type:
2) If a reaction occurs for an alkyl halide in Part A, it will be a (circle one): SN1 or SN2 reaction? How do
each of the following factors affect whether or not (or how fast) a reaction will occur in Exp. 19, Part A?
a. Solvent (same for all alkyl halides in Exp 19, Part A)
b. Nucleophile (same for all alkyl halides in Exp 19, Part A)
c. Structure of the alkyl halide (will vary in Exp 19, Part A)
d. Leaving group (may vary in Exp 19, Part A)
Results
3) Now we are ready to consider the alkyl halides that were tested in Exp 19, Part A.
a. Draw the bond-line structures of each alkyl halide tested (note: crotyl chloride, tube 6, was
omitted).
b. **Read the procedure**, view the video of the experiment and record the results. Be sure to
include the results at room temperature AND elevated temperature when appropriate.
c. For the alkyl halides that reacted, draw the bond-line structures of the major organic product.
d. Finally, for each tube (regardless of whether or not a reaction occurred), explain the results.
Your analysis should be based on structure, the mechanism of the organic reaction occurring
(or not occurring) and the factors that affect the rate law of that reaction type. You may find
words and drawings are helpful for a complete explanation.
Tube
#
Bond-line Structure of
Alkyl Halide
Result(s) Bond-line Structure of
Product
(or “NA” if no reaction)
Analysis ( = an Explanation, based
on structure)
1
2
3
4
5
7
8
9
10
Reflect
4) Refer back to Figure 1. Would we have been able to analyze whether or not the organic reaction
occurred without the “general chemistry reaction” (part b)? Why or why not? (Answer in one
sentence.)
5) Consider crotyl chloride, shown below.
a. Draw a complete curved arrow mechanism for how crotyl chloride could react under the
conditions of this experiment.
b. Provide the structures of all products (organic and inorganic).
c. Then, predict: would you expect to observe a reaction for crotyl chloride under these
conditions? Explain your answer in one sentence.
NaI
Cl
acetone
Prediction (select one):
A reaction would NOT be observed at any
temperature.
A reaction would only be observed at
elevated temperature.
A reaction would be observed at BOTH room
and elevated temperatures
crotyl chloride
all products (organic and inorganic)
complete curved-arrow mechanism leading to the proposed products:
Explanation for prediction:
6) For each pair of reactions: draw the structure of the substitution product, circle the reaction that
would proceed with the fastest rate (if they have the same rate, circle “same”), and explain your
answer in one sentence, referring to structure, mechanism, and rate law.
a)
NaI
NaI
Cl
Br
acetone
same
acetone
explanation:
b)
I
I
NaCN
NaCN
same
acetone
acetone
explanation:
Part B. Silver Nitrate in Ethanol
Introduction
1) Before we analyze the data associated with Experiment 19, Part B, let’s be sure that we understand the
chemical reactions being observed. Although we will not be testing 1-bromo-1-methylcyclopentane,
shown below, it would be expected to undergo substitution under the reaction conditions of the
experiment.
a. First, the alkyl bromide would undergo an “organic chemistry elementary step.” On the figure
below, draw the curved arrows for this step, provide the structures of all intermediates (organic
and inorganic) and name the elementary step.
b. One of products of step 1 undergoes a reaction type that you considered in general chemistry
class. On the figure below, name the type of reaction and provide the identity of the white
powder that would be observed had we studied this alkyl halide in the experiment.
c. The other product of step 1 continues to undergo a series of “organic chemistry elementary
steps.” Draw the complete curved-arrow mechanism for these steps, naming each one (see:
Organic Chemistry Elementary Steps). Circle the final organic product of this reaction.
Figure 2. How 1-bromo-1-methylcyclopentane would react under the conditions of Exp. 19, Part B.
“general” chemistry
reaction type:
a)
“organic” chemistry
elementary step 1:
b)
Br
EtOH, AgNO3(EtOH)
EtOH, AgNO3(EtOH)
intermediate(s)
white precipitate
c)
the rest of the mechanism (label each elementary step with its name and circle the final organic product):
2) If a reaction occurs for an alkyl halide in Part B, it will be a (circle one): SN1 or SN2 reaction? How do
each of the following factors affect whether or not (or how fast) a reaction will occur in Exp. 19, Part B?
a. Solvent (same for all alkyl halides in Exp 19, Part B)
b. Nucleophile (same for all alkyl halides in Exp 19, Part B)
c. Structure of the alkyl halide (will vary in Exp 19, Part B)
d. Leaving group (may vary in Exp 19, Part B)
Results
3) Now we are ready to consider the alkyl halides that were tested in Exp 19, Part B.
a. Draw the bond-line structures of each alkyl halide tested (note: crotyl chloride, tube 6, was
omitted).
b. **Read the procedure**, view the video of the experiment and record the results. Be sure to
include the results at room temperature AND elevated temperature when appropriate.
c. For the alkyl halides that reacted, draw the bond-line structures of the major organic product.
d. Finally, for each tube (regardless of whether or not a reaction occurred), explain the results.
Your analysis should be based on structure, the mechanism of the organic reaction occurring
(or not occurring) and the factors that affect the rate law of that reaction type. You may find
words and drawings are helpful for a complete explanation.
Tube
#
Bond-line Structure of
Alkyl Halide
Result(s) Bond-line Structure of
Product
(or “NA” if no reaction)
Analysis ( = an Explanation, based
on structure)
1
2
3
4
5
7
8
9
10
Reflect
4) Refer back to Figure 1. Would we have been able to analyze whether or not the organic reaction
occurred without the “general chemistry reaction” (part b)? Why or why not? (Answer in one
sentence.)
Do you expect that crotyl chloride would react under the conditions of Part B? Why or why not?
(Explain your answer with clearly drawn structures, referring to the rate law of this reaction).
5)
Cl
crotyl chloride
6) For each pair of reactions: draw the structure of the product, circle the reaction that would proceed
with the fastest rate (if they have the same rate, circle “same”), and explain your answer in one
sentence, referring to structure, mechanism, and rate law.
a)
Cl
Br
EtOH
EtOH
same
explanation:
b)
I
I
same
EtOH
EtOH
explanation:
Summarize and Reflect
You do not need to submit your answers to these questions, but you should take the time to answer them.
1) What did you learn in this experiment?
2) Overall, did alkyl halides undergo only one type of substitution reaction (only react in either part A or
part B) or did some alkyl halides undergo both types of substitution reactions (react in both parts A and
B)? Can you describe any patterns?
3) Consider the factors that affect the rate of substitution reactions (make a list). For each factor consider
if it affects the rates of SN1 and SN2 in the same or different ways (or not at all).
4) What questions do you have?
