Organic Chemistry SN1 SN2 Reaction With Alkyl Halide

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DATA SECTION

 

1. SN2 Conditions – Reaction with NaCN.

 

In this part of the experiment, different alkyl halides were treated with LiCN according to the general reaction shown below. The reaction was carried out in DMSO-d6 at 25°C, and after 10 min, a 1H NMR spectrum was taken and the peaks integrated.

 

(You may also find this reaction in Remote Learning Topic 5.ppt on D2L. Look for the red box.)

The spectra are shown on pages 1-2 in the data pages file. Note that the spectra are of the reaction mixture (without purification), so we should expect to see peaks from both the reactant – alkyl halide and the product – alkyl nitrile.

 

For the reactions with 1-halobutanes and 2-halobutanes, only the signals for the CH2X (from reactant) and CH2CN (from product) are shown, while for the tert-butyl halides, the methyls (from reactant and product, respectively) are shown.

Notice that So for each set of three reactions (Trials 1-3, Trials 4-6, and Trials 7-9), the same product is obtained despite which halogen was used.You should first identify the product structure, then find the product’s signal CH2CN, as that will be the signal that is at the same ppm in each of the 3 spectra.

The red decimal numbers above each peak is the corresponding integration.

For trial 10, you need look back in 1-9, and find the trend of the relative chemical shifts of CH2X and CH2CN. Make an “educated guess” of which peak is from the reactant and which from the product.

 

Here are your tasks:

 

1. Determine the percent conversion for the reaction, using the formula below (“S. mat.” Stands for “reactant”):

 

 

 

2. Calculate the percent conversion for each reaction, and enter it in Table 1. Summary of results 1-10 below.

3. Rank the reactivity based on the calculated percent conversion – highest percent conversion gets number 1 reactivity, whereas lowest percent conversion gets number 10 reactivity. Place your ranking in the last column of table 1.

4. complete the remaining columns in the table.

 

 

 

2. SN1 Conditions – Reaction with CH3OH.

 

In this part of the experiment, different alkyl halides were treated with CH3OH according to the general reaction shown below. The reaction was carried out in CH3OH at 25°C, and after 10min, a portion of the reaction mixture was analyzed by GC.

 

The chromatograms are shown on pages 4-5 in the data pages file.

Same scenario, notice that from the reaction above, the same product is obtained despite what type of alkyl halide was used for each set (Trials 20-22, Trials 23-25, and Trials 26-28). You should first identify the product structure, then the product signal, as that will be the signal that is at the same ppm retention time in the 3 chromatograms of the same set of trials (note that some peaks could be really, really tiny….).

Beside each chromatogram, a table of peak retention times and areas (aka integrations) are shown.

For trial 29, you need look back in 22-28, and find the trend of the relative retention times of RX and ROCH3. Make an “educated guess” of which peak is from the reactant and which from the product.

 

Here are your tasks:

 

1. Determine the percent conversion for the reaction, using the formula below (“S. mat.” Stands for “reactant”):

 

 

 

2. Calculate the percent conversion for each reaction, and enter it in Table 2. Summary of results 20-29 below.

3. Rank the reactivity based on the calculated percent conversion – highest percent conversion gets number 1 reactivity, whereas lowest percent conversion gets number 10 reactivity. Place your ranking in the last column of table 2.

4. Complete the remaining columns in the table.

 

 

 

3. Role of Nucleophile #1 – Reaction of 1-chlorobutane.

 

In this part of the experiment, 1-chlorobutane was treated with different nucleophiles according to the general reaction shown below. The reaction was carried out in acetone (similar to DMSO) at 25°C.

 

 

CH3CH2CH2Cl

+

Nu- Na+

 

 

 

 

 

 

 

 

 

 

 

CH

3

CH

2

CH

2

CH

2

Nu

+

Na+ Cl-

 

 

Since the byproduct NaCl is not soluble in acetone, a precipitate will form as the reaction occurs.

 

Here are your tasks:

 

Given below is a table that gives the time until a precipitate was observed, and from this data, rank the relative reactivity of nucleophiles (shortest time means fastest reaction, which gets number 1 reactivity, whereas longest time means slowest reaction, which gets number 10 reactivity).

 

 

Nucleophile (Nu) Time until precipitate observed Relative reactivity
NaOCH3 0.52 sec  
HOCH3 none observed  
NaSCH3 0.15 sec  
HSCH3 4.35 min  

 

 

 

 

 

4. Role of Nucleophile #2 – Reaction of tert-butyl p-nitrophenyl ether.

 

In this part of the experiment, tert-butyl p-nitrophenyl ether was treated with different nucleophiles according to the general reaction shown below. The reaction was carried out in ethanol (similar to CH3OH) at 25°C.

 

 

The byproduct -OC6H4NO2 has an intense yellow color, while the starting materials are colorless, so the appearance of a yellow color indicates the reaction is occurring.

 

Here are your tasks:

 

Given below is a table that gives the observed results, and from this data, rank the relative reactivity of nucleophiles. (shortest time means fastest reaction, which gets number 1 reactivity, whereas longest time means slowest reaction, which gets number 10 reactivity). Note that we could have “ties”.

 

 

Nucleophile (Nu) Data observed Relative reactivity
NaOCH3 Yellow after 0.52 sec  
HOCH3 Very bright yellow immediately  
NaSCH3 Yellow after 0.52 sec  
HSCH3 Faint bright yellow immediately  

 

 

 

Table 1. Summary of results 1-10

 

Trial

  

Alkyl Halide

 Line Structure of

Compound

 Type of Alkyl Halide

(1°, 2°, or 3°)

 Percent Conversion Relative

Reactivity
1 1-chlorobutane        
2 1-bromobutane        
3  

1-iodobutane

 

        
4  

2-chlorobutane

 

        
5 2-bromobutane        
6 2-iodobutane        
7 tert-butyl chloride        
8 tert-butyl bromide        
9 tert-butyl iodide        
10 Chlorocyclobutane        

Table 2. Summary of results 20-29

 

Trial

  

Alkyl Halide

 Line Structure of

Compound

 Type of Alkyl Halide

(1°, 2°, or 3°)

 Percent Conversion Relative

Reactivity
20 1-chlorobutane        
21 1-bromobutane        
22  

1-iodobutane

 

        
23  

2-chlorobutane

 

        
24 2-bromobutane        
25 2-iodobutane        
26 tert-butyl chloride        
27 tert-butyl bromide        
28 tert-butyl iodide        
29 allyl chloride        

 

DATA ANALYSIS

 

SN2 Reactions.

 

4. Answer each of the following questions completely but briefly. Be sure to use your data and to note any discrepancies in your data.

 

a. Looking at trials 1, 4, and 7, what conclusion can you draw about the type of alkyl chloride (1o, 2o, or 3o) employed and the rate at which the SN2 reaction occurs? Explain why this might be.

 

 

 

 

 

 

 

 

 

 

b. Looking at trials 2, 5, and 8, is the trend the same or different with the alkyl bromides (so compare with trials 1, 4, 7, in terms of the halide type)? Also look at trials 3, 5, and 9 – is the trend the same or different with the alkyl iodides (again, in terms of the halide type, please)? Does these results make sense?

 

 

 

 

 

c. Comparing the trend in trials (1 to 2 to 3), does the type of halogen have an effect on the reaction? If so, what is the trend? Do you see the same trend in comparing trials 4 to 5 to 6 (in terms of the halogen type)? How about trials 7 to 8 to 9 (in terms of the halogen type)? Explain the effect, or lack of effect, of the alkyl halide.

 

 

 

 

 

 

d. Comparing trials 4 and 10, is there a difference in the halide type? And is there a difference in the rates? If there is, explain why there is a difference in the rate. (Hint: think about the mechanism and molecular structures of 4 and 10)

 

 

 

 

e. Compare the chemical shift of the signal for the alkyl halides in trials 1, 2, and 3 (from the data file). Is there a trend? If so, what is it and does it make sense?

SN1 Reactions.

 

5. Answer each of the following questions completely but briefly. Be sure to use your data and to note any discrepancies in your data.

 

a. Looking at trials 20, 23, and 26 what conclusion can you draw about the type of alkyl chloride (1o, 2o, or 3o) employed and the rate at which the SN1 reaction occurs? Explain what conclusion you can draw about the stability of carbocations from this data.

 

 

 

 

 

 

 

f. Looking at trials 21, 24, and 27, is the trend the same or different with the alkyl bromides (so compare with trials 1, 4, 7, in terms of the halide type)? Also look at trials 22, 25, and 28 – is the trend the same or different with the alkyl iodides (again, in terms of the halide type, please) (again, in terms of the halide type, please)? Does these results make sense?

 

 

 

 

 

g. Comparing the trend in trials (20 to 21 to 22), does the type of halogen have an effect on the reaction? If so, what is the trend? Do you see the same trend in comparing trials 23 to 24 to 25 (in terms of the halogen type)? How about trials 26 to 27 to 28 (in terms of the halogen type)? Explain the effect, or lack of effect, of the alkyl halide.

 

 

 

 

 

 

h. Comparing trials 21 and 29, is there a difference in the halide type? And is there a difference in the rates? If there is, explain why there is a difference in the rate. (Hint: think about the mechanism and the intermediate structures)

 

 

 

i. Compare the retention times in trials 21, 22, and 23. Is there a trend (in terms of halogen), and if so, can you explain it?

 

 

 

j. Compare the retention times in trials 21, 24, and 27. Is there a trend (in terms of halide type), and if so, can you explain it?

 

 

 

Comparison of SN1 and SN2 Reactions.

 

6. Is the trend in the reactivity between leaving groups (Br vs Cl) the same or different between the SN1 and SN2 experiments? Does this make logical sense to you? Explain.

 

 

 

 

 

 

 

 

 

 

 

 

7. a. Is the trend in the reactivity with different degrees of substitution (1°, 2°, and 3°) the same or different between the SN1 and SN2 experiments? Does this make logical sense to you? Explain.

 

 

 

 

 

 

 

 

 

 

b. Based on your answer to 7a, for which type of alkyl halide (1°, 2°, or 3°) will it be the most difficult to control the type of substitution reaction (SN1 and SN2) it undergoes?

 

 

 

 

 

Effect of the Nucleophile.

 

8. Explain the relationship between the strength of the nucleophile (see also in RLT 5.ppt on D2L) and the reactivity based on the results in the table in part 3 Role of Nucleophile #1 – Reaction of 1-chlorobutane.

 

 

 

 

 

 

 

9. Explain the relationship between the strength of the nucleophile (see also in RLT 5.ppt on D2L) and the reactivity based on the results in the table in part 4 Role of Nucleophile #2 – Reaction of tert-butyl p-nitrophenyl ether.

 

RX + LiCN RCN

RX + CH

3

OH ROCH

3

(CH

3

)

3

COC

6

H

4

NO

2

+ Nu (CH

3

)

3

CNu +

–

OC

6

H

4

NO

Vegetarianism

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Vegetarianism

Answer the following questions related to Vegetarianism.

  • In the United States, 32% of adults eat a vegetarian diet (Vegetarianism in America, n.d.). What does the term “vegetarian” mean?
  • Do you think vegetarian diets are practical? That is, can someone easily be a vegetarian while living the typical American life of being rushed and busy?
  • Vegetarian diets are associated with a lower risk of obesity and diabetes as well as other chronic conditions (Marsh, Zeuschner, & Saunders, 2012). Clearly a vegetarian diet can be a healthy one, but can a vegetarian diet lack nutrients? If so, which nutrients may be lacking? How could these nutrients be measured in the body to determine if someone is deficient in them? Are there vegetarian foods that provide these nutrients or would supplementation be necessary? Are there any interactions to be aware of with the supplements that a vegetarian may take?
  • Do you think that a vegetarian diet would be costlier than a nonvegetarian diet?
  • Look at the meals you ate in your 3-days diet record. Do any of your meals contain no meat? Choose one of your meals that contain meat and modify it to be vegetarian. Would you eat the modified meal?

References:

Marsh, K., Zeuschner, C., & Saunders, A. (2012). Health implications of a
           vegetarian diet: A review. American Journal of Lifestyle Medicine, 6(3),
           250–267.

Vegetarianism in America. (n.d.). Vegetarian Times. Retrieved from
           http://www.vegetariantimes.com/article/vegetarianism-in-america/

Crystal Structure Activity

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Crystal Structure Activity Learning Objectives After this activity, students should be able to

1. Identify different layering patterns that lead to the cubic unit cells, determine coordination

numbers, and compute packing efficiencies for atomic solids.

2. Determine the empirical formula of an ionic compound from its crystal structure.

Overview Use the visualization tool found at https://atom.calpoly.edu/crystal/ and answer the following

questions. Many of the functions in the simulation are bound to keys; look at Key Controls for the list.

The simulation starts by default with the Simple cubic lattice screen. The drop-down menu allows you

to view other lattice structures. You can rotate the structure and view it from different sides by holding

the mouse and dragging the structure. You can also zoom in and out with the mouse wheel. There are

two important modes that are controlled with the Expansion slider at the bottom of the screen. In

Layering mode, you can see how the 3D crystal lattice can be made by stacking layers of atoms. In Unit

Cell mode, you can see how the 3D lattice is composed of repeating unit cells with fractional atoms.

Lattice Structures of Atomic Solids

Layering We will begin this activity by looking at the layering pattern of particles that gives rise to each of the

cubic unit cells. A unit cell is the smallest unit in a repetitive pattern that makes the 3-dimensional lattice

structure. As shown in Figure 1, there are two basic 2D patterns for layers of atoms. The atoms in each

layer can be packed in a square array, or “close-packed” with a rhombus representing the simplest

repeating pattern. When multiple layers of a particular 2D pattern are stacked together, they can

generate a variety of 3D patterns, depending on how the layers are shifted relative to each other. If the

layers repeat identically as they stack, this can be described as “aa” stacking. If the second layer is

staggered relative to the first layer, but the third layer is stacked directly above the first layer, this

stacking pattern is described as “aba.” You can explore this layering effect by selecting Layering on the

left of the visualization tool and using the Expansion slider.

Figure 1. Square and rhombic unit cells in 2D layers.

For each of the cubic lattices (simple cubic, body-centered cubic, and face-centered cubic), answer the

following questions. Use the visualization tool to help.

 

 

1. What type of 2D unit cell exists in each layer, square or rhombic? (See Figure 1).

2. What is the stacking pattern in the corresponding lattice structure? (use letters a, b, c, etc. to label

different layers).

Unit Cells Once atoms are stacked into a 3D crystal lattice, the simplest repeating geometric pattern—the unit

cell—will usually contain fractions of atoms. While only whole atoms exist in the crystal, the geometric

representation of the unit cell will have atoms split between multiple neighboring unit cells. To find a

unit cell, we take the smallest repeating pattern and “slice” the shared parts off, to make it look like a

cube (here we are exploring cubic unit cells, but there are shapes for unit cells as well). With Unit Cell

selected on the left, use the Expansion slider to see how multiple unit cells together makes up an entire

lattice. To highlight a single unit cell within the crystal lattice, press “t” on the keyboard to toggle the

translucency.

For each of the cubic lattices, answer the following questions.

1. Which part(s) of a 3D unit cell do the atoms occupy (corner, edge, center, face)?

2. What fraction of an atom does each contribute to the unit cell?

3. What is the total number of atoms per unit cell?

Coordination Number The coordination number is the number of closest neighbors an atom has in the lattice, including atoms

in the adjacent unit cells. For the following questions, you can use the Coordination mode in the

visualization tool to verify your answer.

1. Determine the coordination number for the simple cubic lattice.

2. Determine the coordination number for the grey atoms in a body-centered cubic (bcc) lattice.

3. Determine the coordination number for the red atoms in a bcc lattice.

4. Explain why the coordination number for all the atoms in the bcc lattice is the same.

5. Determine the coordination number for the face-centered cubic lattice.

Packing Efficiency Since the layering pattern in all of the lattices leaves empty space between the particles, the unit cell is

not completely occupied by atoms (here we are treating atoms like hard spheres). The packing

efficiency, which is the percentage of occupied space in the cube, is not 100%. The packing efficiency is

not the same for all 3 cubic lattices. A more densely packed unit cell will have a higher packing efficiency

than a less densely packed one. The packing efficiency of a lattice structure measures how well the

space inside of a unit cell is utilized. It is the percent ratio of volume occupied by the particles in a unit

cell to its total volume.

𝑃𝑎𝑐𝑘𝑖𝑛𝑔 𝐸𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦 = 𝑉𝑜𝑐𝑐𝑢𝑝𝑖𝑒𝑑

𝑉𝑡𝑜𝑡𝑎𝑙 × 100

The occupied volume is related to the number of particles occupying the cell and their location within

the cell. The edge length of each unit cell is derived using the trigonometric relationships shown in

Figure 2.

 

 

 

Figure 2. Geometric relationships showing how the edge length is related to the atomic radius for simple cubic, body-centered cubic, and face-centered cubic unit cells.

Unit Cell Edge length in terms of radius

Simple cubic 𝑙 = 2𝑟

Body-centered cubic 𝑙 = 4𝑟

√3

Face-centered cubic 𝑙 = 2√2𝑟

 

𝑉𝑜𝑐𝑐𝑢𝑝𝑖𝑒𝑑 = (# 𝑝𝑎𝑟𝑡𝑖𝑐𝑙𝑒𝑠) × 4

3 𝜋𝑟3

𝑉𝑡𝑜𝑡𝑎𝑙 = 𝑙 3

Answer the following questions. Assume that the lattice consists of only one type of atom, and the

radius of this atom is r.

1. Assume an atom is a perfect sphere. In terms of r, what volume of the simple cubic unit cell is

occupied by atoms?

2. What is the total volume of the simple cubic unit cell?

3. Determine the packing efficiency of a simple cubic unit cell. Use your answers from the previous

two questions.

4. Determine the packing efficiency for a body-centered cubic unit cell.

5. Determine the packing efficiency for a face-centered cubic unit cell.

6. Observe the difference in stacking patterns of the unit cells and note how they are related to the

packing efficiency.

Summary

2D layer pattern

(square vs rhombic)

Stacking Pattern (e.g.

aba)

Number of Atoms per Unit Cell

Coordination Number

Packing Efficiency

Simple Cubic

Body-Centered Cubic

Face-Centered Cubic

 

 

Lattice Structures of Ionic Compounds Now we will look at a few examples of ionic solids. The Legend button will show the ion coloring

scheme. The ions are roughly scaled to their relative ionic radii within each of the lattices.

Sodium Chloride 1. Determine the number of sodium ions per unit cell.

2. Determine the number of chloride ions per unit cell.

3. What is the empirical formula of sodium chloride based on the relative number of each ion in

the unit cells?

4. Is the empirical formula determined from the lattice structure in agreement with the one

predicted by the typical ion charges?

5. Are either of the ions arranged in one of the basic cubic unit cells (simple, body-centered, face-

centered)?

Calcium Fluoride 1. Determine the number of calcium ions per unit cell.

2. Determine the number of fluoride ions per unit cell.

3. What is the empirical formula of calcium fluoride based on the relative number of each ion in

the unit cells?

4. Is the empirical formula determined from the lattice structure in agreement with the one

predicted by the typical ion charges?

5. Are either of the ions arranged in one of the basic cubic unit cells (simple, body-centered, face-

centered)?

Organic Chemistry 1 Test

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Question 1:

Fill the boxes with the products obtained or the reagents needed. Make sure to include the correct

stereochemistry where it is needed. (2 points each) 20 pts

 

 

 

 

 

 

A= E=

 

 

B-= F=

 

 

 

 

C= G=

 

 

 

D= H=

 

 

 

 

 

 

Which one of the following molecules is susceptible to autooxidation faster? Explain your

choice by drawing the corresponding free radical intermediate. 4 pts)

 

 

 

 

 

 

 

 

Question 2

Identify the intermediate molecules A, B and C for the following transformations. 6 pts

 

 

 

 

 

C= B= A =

 

 

 

 

Devise a method to prepare 3-bromo-1-propanol from 2-bromopropane. 6 pts

(No mechanism needed, only draw the reagents and intermediate molecules)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Question 3:

Predict the product(s) including stereochemistry and propose a mechanism for the following reaction:

(draw only initiation and propagation steps) 9 pts

 

 

 

 

 

 

 

 

 

 

MECHANISM:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

An unknown compound, A, has the molecular formula C8H14. Catalytic hydrogenation of A with H2/Pt

yields a product with the molecular formula C8H18 (B). Upon ozonolysis (O3, H2O) A gives one product C.

What are the structures of A, B and C? (show your work) 6 pts

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Predict the products (include stereochemistry) when following compound is treated with NBS and

irradiated with UV light. If Br2 and light had been used, what competing reaction would have occurred

(list the products of that reaction too).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Extra Credit: Propose a mechanism for the following reaction. 5 pts