Nucleophilic Substitutions PDF

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Lab #8: Nucleophilic Substitution Reactions: Mechanisms and Synthesis Clarisbel Hernandez Nova Yahaira Reyes October 22nd, 2020.

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Purpose: The purpose of this experiment is to change 2-methyl-2-butanol to tert-amyl by the use of hydrochloric acid. Also, looking at SN1 and SN2 mechanisms compare the reactivity of alkyl halides.

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Introduction: A nucleophilic substitution reaction can occur by two different mechanisms, SN1 or SN2. The SN1 mechanism is a unimolecular nucleophilic substitution, which requires the process to be completed in two steps. On the other

hand, the SN2 mechanism, is a bimolecular nucleophilic substitution, which only takes one step to complete. Deciding which mechanism will occur depends on the leaving group, nucleophile, and solvent. This experiment is divided into two parts, the first one is the preparation of tert-amyl chloride, and the second is the relative reactivity of alkyl halides. During the second part, the alkyl halides will be reacting with ethanolic silver nitrate, and NaI in acetone. T The alkyl halides that will be compared are t-butyl chloride, Allyl chloride, n-butyl bromide, n-butyl chloride, and sec-butyl chloride.

SN1 Reaction:

SN2 Reaction:

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Procedures: Procedures were followed as stated in the lab manual

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Table of Physical Constants:

Name

2-methyl-2-

Structure

MF

MW (g/mol)

D (g/

C5H12O

88.15

mL) 0.81

HCl

36.46

1.19

butanol Hydrochloric Acid

Tert-amyl

C5H11Cl

106.60

0.87

n-butyl chloride

C4H9Cl

92.57

-

Sec-butyl chloride

C4H9Cl

92.57

-

Chloride

t-butyl chloride

C4H9Cl

92.57

-

n-butyl bromide

C4H9Br

137.02

-

Allyl chloride

C3H5Cl

76.52

-

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Results/ Data:

Part I: Synthesis: Preparation of tert-Amyl Chloride t-amyl alcohol mL added 12 mL grams 9.7 g moles 0.11 mol Moles of t-amyl chloride (1:1 ratio) 0.11 mol Grams of t-amyl chloride 11.75 g Limiting or excess reagent Limiting Theoretical yield 11.75 g Experimental grams of product 4.08 g Percent yield 34.72% Reaction: 

Calculations: 12mL C5H12O x (0.81 g C5H12O/1 mL) = 9.72 g. C5H12O 9.72 g. C5H12O x (1 mol/ 88.15 g) =0.11 mol C5H12O M= mol/liters of solution 12M= mol/0.02L= 0.24 mol HCl 0.24 mol HCl x (36.46 g HCl/ 1 mol HCl) = 8.75 g HCl

HCl (12 M used) 20 mL 8.75 g 0.24 mol 0.24 mol 25.58 g Excess

12mL C5H12O x (0.81 g C5H12O/ 1 ml C5H12O) x (1 mol C5H12O/ 88.15 g C5H12O) x (1 mol C5H11 Cl/ 1 mol C5H12O) x (106.60 g C5H11 Cl/ 1 mol C5H11 Cl) = 11.75 g C5H11 Cl 0.24 mol HCl x (1 mol C5H11 Cl/ 1 mol HCl) x (106.60 g C5H11 Cl/ 1 mol C5H11 Cl) = 25.58 g C5H11 Cl P.Y= (Actual/ Theoretical)x 100%= (4.08/11.75)x 100%= 34.72%

Observations/notes: HCl was added to the alcohol in order to catalyze it.

Part II: Comparison of the Reactivity of Alkyl Halides

Part A: Alkyl Halides and SN1 Conditions- AgNO3/EtOH Reactions Time Alkyl Halide Structure 1o, 2o, 3o alkyl halide, precipitate or other formed

Observations

n-butyl chloride

1o

4

This was the slowest one, was expected not to react.

sec-butyl chloride

2o

5

Intermediate reaction time

t-butyl chloride

3o

1

Reacted quickly

n-butyl bromide

1o

3

This was the slowest one, was expected not to react.

Allyl chloride

Allyl halide, 1o

2

Reacted quickly

Ranking for SN1 Reactions from most reactive alkyl halide to least: t-butyl chloride, Allyl chloride, n-butyl bromide, n-butyl chloride, sec-butyl chloride. Reactions (if any):

Part B: Alkyl Halides and SN2 Conditions- Finkelstein NaI/acetone Reactions Time Observations Alkyl Halide Structure 1o, 2o, 3o

alkyl halide, or other

precipitate formed

n-butyl chloride

1o

3

Intermediate reaction time

sec-butyl chloride

2o

5

This was the slowest one to react

t-butyl chloride

3o

4

This was expected not to react, however reacted faster than secbutyl chloride.

n-butyl bromide

1o

2

Intermediate reaction time

Allyl chloride

Allyl halide, 1o

1

This one was the fastest to react

Ranking for SN2 Reactions from most reactive alkyl halide to least: Allyl Chloride, n-butyl bromide, n-butyl chloride, t-butyl chloride, and sec-butyl chloride.

Reactions (if any):...