CHE 276 Lab 9 Report- Nucleophillic Substitution PDF

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Organic chemistry lab report: Full marks (edited from feedback to correct any mistakes). Detailed report with pre-lab and post-lab, correct formatting, and calculations....

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Experiment 9: Nucleophilic Substitution TA: Pankaj, Yiran Reaction:

Nov 9, 2020

Experiment 9: Nucleophilic Substitution

Nov 9, 2020

Compounds Compound

Molecular Weight (g/mol)

Melting Point (Cº)

Boiling Point (°C)

Density (g/mL or g/cm3)

1-bromobutane

137.02

-112

104

1.276

2-bromobutane

137.02

-112

91

1.255

2-bromo-2-methylpropane

137.02

-20

73

1.22

1-chlorobutane

92.57

-123

78

0.886

2-chlorobutane

92.57

-140

70

0.873

2-chloro-2-methylpropane

92.57

-25

51 - 52

0.851

Bromobenzene

157.01

-31

156

1.491

1-chloro-2-methylpropane

92.57

-131

68 - 69

0.883

1-chloro-2-butene

90.55

78 - 83

84 - 85

0.929

Sodium Iodide (NaI)

149.89

661

1304

3.67

Acetone

58.08

-94

56

0.791

Silver Nitrate (AgNO3)

169.87

212

440

3.89

Ethanol

46.07

-114

78.3

0.789

Safety Chemical

Safety hazards

1-bromobutane

Highly flammable

Experiment 9: Nucleophilic Substitution

Skin and eye irritation 2-bromobutane

Highly flammable

2-bromo-2-methylpropane

Highly flammable

1-chlorobutane

Highly flammable Harmful if swallowed

2-chlorobutane

Highly flammable

2-chloro-2-methylpropane

Highly flammable

Bromobenzene

Highly flammable Skin irritant

1-chloro-2-methylpropane

Highly flammable

1-chloro-2-butene

Highly flammable Corrosive Can cause skin and eye damage

Sodium Iodide (NaI)

Can cause skin and eye damage

Acetone

Highly flammable

Silver Nitrate (AgNO3)

Corrosive

Ethanol

Highly flammable

References: pubchem.ncbi.nlm.nih.gov

Procedure:

Nov 9, 2020

Experiment 9: Nucleophilic Substitution

A. SN2 Reactions (NaI in Acetone) 1. Primary structure: a. In four test tubes, add 2mL of 15% NaI in acetone b. Add 2 drops of alkyl halides in each test tube. Note time. c. Add stopper, mix the tube, and observe any precipitation d. Record time taken for precipitate to form e. Heat the tubes without precipitate in a water bath for 5 minutes f. Cool the tubes to room temperature g. Observe any precipitation 2. Secondary structure: a. Repeat steps 1a-1g. 3. Leaving group: a. Repeat steps 1a-1g. B. SN1 Reactions 1. Primary structure a. In four test tubes, add 2mL of 1% AgNO3 in ethanol b. Add stopper, mix the tube, and observe any precipitation c. Record time taken for precipitate to form d. Heat the tubes without precipitate in a water bath for 5 minutes e. Cool the tubes to room temperature f. Observe any precipitation 2. Secondary structure: a. Repeat steps 1a-1g. 3. Leaving group: a. Repeat steps 1a-1g. 4. Solvent a. Label two test tubes as 1% AgNO3 in ethanol and 1% AgNO3 in 50% ethanol and 50% water. b. Add 2 drops of 2-chlorobutane to tubes. Note time. c. Add stopper, mix the tube. d. Record observations

Data and Calculations: Primary group:

Nov 9, 2020

Observations:

Experiment 9: Nucleophilic Substitution

Nov 9, 2020

NaI in Acetone (SN2)

Reactivity RT

50℃

Time (s)

Amount

1-bromobutane (1)

√

-

160

+++

2-bromobutane (2)

-

√

240

++

2-bromo-2-methylpropane (3)

-

√

200

++

bromobenzene (7)

-

-

-

-

1-bromobutane (1)

√

-

180

+

2-bromobutane (2)

√

-

5

++

2-bromo-2-methylpropane (3)

√

-

1

++

bromobenzene (7)

-

-

-

-

AgNO3 in Ethanol (SN1)

Secondary group: NaI in Acetone (SN2)

Reactivity RT

50℃

Time (s)

Amount

1-chlorobutane (4)

-

√

300

+

1-chloro-2-methylpropane (8)

-

-

-

-

1-chloro-2-butene (9)

√

-

30

+++

1-chlorobutane (4)

-

-

-

-

1-chloro-2-butene (9)

√

-

1

+++

AgNO3 in Ethanol (SN1)

Leaving group: NaI in Acetone (SN2)

1-bromobutane (1)

Reactivity RT

50℃

Time (s)

Amount

√

-

160

+++

Experiment 9: Nucleophilic Substitution

Nov 9, 2020

2-bromobutane (2)

-

√

240

++

1-chlorobutane (4)

-

√

300

+

2-chlorobutane (5)

-

-

-

-

2-bromobutane (2)

√

-

5

++

2-bromo-2-methylpropane (3)

√

-

1

++

2-chlorobutane (5)

-

-

-

-

2-chloro-2-methylpropane (6)

√

-

1

+++

AgNO3 in Ethanol (SN1)

Solvent group: 1% AgNO3 in Ethanol (SN1)

2-chlorobutane (5)

Reactivity RT

50℃

Time (s)

Amount

-

√

540

+

-

√

60

+

1% AgNO3 in 50% Ethanol/50% Water (SN1) 2-chlorobutane (5)

Discussion/ Conclusion: For the discussion, the following substances are labeled as such: (1) 1-bromobutane (2) 2-bromobutane (3) 2-bromo-2-methylpropane (4) 1-chlorobutane (5) 2-chlorobutane (6) 2-chloro-2-methylpropane (7) Bromobenzene

Experiment 9: Nucleophilic Substitution

Nov 9, 2020

(8) 1-chloro-2-methylpropane (9) 1-chloro-2-butene Effects of primary structure on SN2 reactions: Substrates (1), (2), (3), and (7) were used. (1) formed a precipitate at RT after 160 seconds. (2) and (3) formed a precipitate at 50ºc after 240 seconds and 200 seconds. (7) did not form any precipitate at any temperature. These results mostly support the expectations since the order of reactivity goes down with an increase in steric effects. Since (1) was the fastest and (7) was the slowest, these two substrates followed the expectations. However, since (2) is a secondary structure, it should have formed a precipitate faster than (3), which is a tertiary structure. Effects of secondary structure on SN2 reactions: Substrates (4), (8), and (9) were used. (4) formed a precipitate at 50ºc after 300 seconds. (8) did not form a precipitate at any temperature. (9) formed a precipitate at RT after 30 seconds. The results support the expectations since it was expected that the substrate with the least amount of steric hindrance will form precipitates fast. As (4) and (9) are both primary structures, a backside nucleophile attack could occur. However, because of the steric hindrance present in (8) from the methyl group attached to the carbon, a backside nucleophile attack could not take place. Hence, no precipitate formed. Effects of leaving group on SN2 reactions: Substrates (1), (2), (4), and (5) were used. (5) did not form a precipitate in any temperature. Effects of primary structure on SN1 reactions: Substrates (1), (2), (3), and (7) were used. (1), (2), and (3) formed precipitates after 180 seconds, 5 seconds, and 1 second. The results are consistent with the expectations since it is expected that the order of reactivity increases with higher cation stability. (1), a primary structure had the slowest reaction rate, (2), a secondary structure had a faster reaction rate, and (3), a tertiary structure, had the fastest reaction rate. The reason (7) did not form a precipitate is because the ring structure of the bromobenzene does not allow for a carbocation to form. Effects of secondary structure on SN1 reactions: Substrates (4) and (9) were used. (4) did not form a precipitate at any temperature. (9) formed a precipitate at RT after 1 second. These results are consistent with the predictions. (4) is a primary structure, which means the reaction is extremely weak. (9) forms very stable transition states because it is an allylic halide. Effects of leaving group on SN1 reactions: Substrate (2), (3), (5), and (6) were used. (5) did not form a precipitate at any temperature. (6) formed a precipitate at RT after 1 second, likely because it is a tertiary structure that can form a very stable carbocation. Effects of solvent on SN1 reactions: Substrate (5) was used in 1% AgNO3 in ethanol and 1% AgNO 3 in 50% ethanol/50% water. The mixture with 1% AgNO3 in ethanol formed a precipitate after 540 seconds. The mixture with 1% AgNO3 in 50% ethanol/50% water formed a precipitate in 60 seconds. These results are consistent with the predictions because as water is more polar than ethanol, a precipitate would form faster in water. Questions:

Experiment 9: Nucleophilic Substitution

Nov 9, 2020

Identify a substrate from this study that gave fast reactions for both SN2 and SN1, and explain why it is fast for both. 1-chloro-2-butene gave fast reactions for both SN2 and SN1. It was fast for SN2 because it is a primary structure, reduccing the steric hindrance. It was fast for SN1 because its an allylic halide which means it can form more stable carbocations. Why is iodide such a good nucleophile? Iodide is a good nucleophile because it has a greater atomic radius, allowing it to donate electrons more readily. Bromoethene, shown below, is both unhindered and has a nearby C=C bond. Yet it is unreactive under both SN2 and SN1 reaction conditions. Why? Bromoethene is unreactive under SN2 reaction conditions because the arrangement of bromoethene makes it difficult for a backside nucleophile attack to take place due to the strong Van der Waals repulsion forces. It is unreactive under SN1 reaction conditions because the leaving group ability is weak and hence the cation is unstable....