Lab report experiment 8- The SN2 Reaction: Factors affecting SN2 reaction PDF

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The SN2 Reaction: Factors affecting SN2 reaction.
This goes through the SN2 reaction and the factors that affect it....

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Idelise Melendez Experiment 8 Lab Report: The SN2 Reaction: Factors affecting SN2 reaction

I.

INTRODUCTION: i. Background: An SN2 reaction, or mechanism, is characterized by being bimolecular and concerted (1). This means that the reaction takes place in one step, with no intermediates in between. The general steps of an SN2 reaction are: a nucleophile attaches to a central carbon at the same time that the leaving group breaks the bond between itself and that same carbon. There are certain factors that can affect the speed in which the reaction takes place. Factors that affect SN2 reactions are the strength of the nucleophile and the type of solvent in which the reaction takes place (2). Protic solvents decreases the power of the nucleophiles meaning that it takes longer for the reaction to be completed (3). In protic solvents, the polarizability of the nucleophile, which in this experiment was the group of alkyl halides, makes the reaction occur quicker because there is little steric hinderance. Aprotic solvents will result in a faster SN2 reaction because they lack hydrogen-bond donating capabilities (3). This means that it requires less energy to break the bond between the leaving group and its attached compound.

Figure 1. SN2 Mechanism for the reaction between a primary alkyl halide and trimethylamine

Figure 2. Undesired side reaction that can occur between a primary alkyl halide and triethylamine II.

Collected three test tubes. In the first, acetone, 20 drops triethylamine, and 10 drops methyl iodide were added. Shook test tube vigorously and recorded observation.

EXPERIMENTAL SECTION: i. Procedural Flowchart: In test tube two, 5mL acetone, 20 drops tripropylamine, and 10 drops methyl iodide were added. Shook test tube vigorously and recorded observations.

In test tube three, 5mL acetone, 20 drops ethyldiisopropyl, and 10 drops methyl iodide were added. Shook test tube vigorously and recorded observations.

In test tube one, added 20 drops of triethylamine and 15 drops iodoethane. Shook vigorously and recorded observations.

Determined the melting point, percent yield, and weight of precipitate. Compared these results to known amines and identified the unknown.

III.

Used a vacuum filtration and washed the precipitate that formed with the solvent.

In a clean test tube, added 40 drops of unknown amine, 20 drops of iodomethane, and 2mL of solvent. Allowed the solution to sit for 15 minutes then placed in an ice bath.

In test tube 2, added 20 drops triethylamine and 15 drops 1bromopropane. Shook vigorously and recorded observations.

TABLE OF CHEMICALS: i. Table 1- Chemicals used during experiment

Name

Formul a

Structure

Hazards

-114.7

Boilin g Point (°C) 89

Meltin g Point (°C)

Triethylamine

C6 H 15

Molar Mass (g/mol ) 101.19

Tripropylamine

C 9 H 21

143.27

-94

158.1

Irritant

Ethyildiisopropylami ne

C8 H 1 9

129.24

-46

126.5

Irritant, Flammabl e

Iodoethane

C2 H 5 I

155.97

-111.10

73.3

1-bromo-propane

C3 H 7 B

122.99

-110.5

71

2-bromo-propane

C3 H 7 B

122.99

-89

59

Flammabl e Flammabl e Irritant

Irritant

Acetone

C3 H 6 O

58.08

-95

56

Irritant

Diethyl ether

C 4 H 10

74.12

-116.3

34.6

Irritant

IV.

RESULTS i. Table 2- Reaction of iodomethane with amines Test tube 1triethylamine and iodomethane Fastest

Test tube 2tripropylamine and iodomethane Medium

Test tube 3ethyldiisopropyl and iodomethane Slowest

Speed of precipitate formation ii. Table 3- Reaction of triethylamine with alkyl halides Test tube 1Test tube 2iodomethane 1-bromopropane Fastest Medium Speed of precipitate formation iii. Table 4- Reaction of unknown amine with iodomethane Melting Point of unknown Speed of precipitate Identification of formation Unknown −¿ ¿ 178-180°C Very fast +¿ I ( C6 H 5 )C C H 3 ¿3 ¿ H2 N ¿ V.

DISCUSSION i. This experiment worked with an SN2 reaction and the factors that affected this type of reaction. The steric hinderance of a molecule can greatly affect the reaction speed of that molecule, as seen in this experiment. It was seen when iodomethane was mixed with triethylamine. The reaction between these two was extremely fast, as seen in table 2. This is because iodomethane is a primary substrate, making the steric hinderance very minor. With this being a primary substrate and the triethylamine being a strong nucleophile, the reaction completed quickly. On the other hand, the mixture between ethyldiisopropyl was the slowest and did not create a precipitate. This is between ethyldiispropyl is a weak nucleophile because of its steric hinderance. This did not allow for the reaction to take place as well as those in the other two test tubes. As described in the aforementioned information, the nucleophilicity also played a great role, with triethylamine being the best nucleophile in this group, tripropylamine being second, and ethyldiisopropyl being third. It should be noted that the speed of precipitate formed also followed the pattern of the strength of the nucleophiles.

VI.

VII.

Triethylamine was the fasted whereas ethyldiisopropyl was last. In the reactions with triethylamine and the alkyl halides, shown on table 3, the strength of the leaving group affected the speed of the reaction. Iodine is more polarizable than bromine, which is why the reaction with iodomethane completed faster than that with 1-bromopropane. Once this was completed and the melting point of the salt was tested, the resulting meting point, shown in table 4, was 178-180°C. This was then compared to the chart in the lab manual to obtain the identification of the unknown amine. CONCLUSION i. The theoretical background and the results obtained are connected. It was predicted that steric hinderance and the strength of the nucleophile and leaving group would affect the rate of reaction. The experimental data supports this hypothesis because in the first round of testing, the test tube with the least amount of steric hinderance and stronger nucleophile was the fastest and the test tube with the most steric hinderance and weakest nucleophile was the slowest. In the second round during this experiment, the test tube with the better leaving group—iodine because it is more polarizable—performed the reaction faster than the test tube with bromine. This experiment can also be applied to other aspects in life. SN2 reactions are used to find out what polymers, when bound with others, create a biodegradable material that can be more beneficial for the environment. Overall, this experiment accomplished what it was set out to do. REFERENCES 1. SN2, https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Supplemental_Modul es_(Organic_Chemistry)/Reactions/Substitution_Reactions/SN2 (accessed Mar 4, 2021). 2. Factors That Affect SN2 Reactions, https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Map %3A_Organic_Chemistry_(Bruice)/08%3A_Substitution_Reactions_of_Alkyl_H alides/8.02%3A_Factors_That_Affect_(S_N2)_Reactions (accessed Mar 4, 2021). 3. Polar Protic and Aprotic Solvents, https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Supplemental_Modul es_(Organic_Chemistry)/Fundamentals/Intermolecular_Forces/Polar_Protic_and_ Aprotic_Solvents (accessed Mar 4, 2021)....