I need to develop and test hypotheses concerning the nature of SN1 and/or SN2 re

Question

I need to develop and test hypotheses concerning the nature of SN1 and/or SN2 reactions (I think we are mainly concerned with the reaction kinetics). We will be given a variety of alkyl halides to use to explore this chemistry. I need to use these to develop three different hypotheses (I need 3 in case the instructor or TA rejects one or two of them). Please include the specific experiments I will run to test these and if you are certain that your hypothesis will work you don't need to include 3 different ones (2 would be nice tho). I already have some ideas but just need more input from somebody else. I've included images of the handout given to me in case there are any questions and it also lists the alkyl halides that will be provided. Thank you

2015 Ch 263 2-Credit Org Lab 15T, 15Th & 16T (if needed): Final Lab Practical- SN1 and SN2 Postulates The Pre-lab assignment (50 pts) for the Lab 14T must be sent to your TA no later than November 24 (see below). The lab practical itself is worth 100 points Chemical transformations (reactions; i.e., A B C D) occur via precise reproducible mechanisms. The mechanism may involve the formation of a reactive intermediate followed by a subsequent reaction to form product, followed its reaction to form product, a so-called "stepwise" mechanism. Alternatively, all of bonds may be made and broken in a single step, a so-called "concerted" mechanism. The classic SN1 (substitution nucleophilic unimolecular) and SN2 (substitution nucleophilic bimolecular) substitution reactions nicely illustrate these two extreme-case mechanisms. (It may be useful at this point to review your lecture text for a more complete discussion of substitution reactions.) The SN1 reaction proceeds via rate determining ionization to a carbocation intermediate followed by fast capture by a nucleophile (weak or strong). In the SN2 reaction, the bond between the strong nucleophile and the electrophile forms as the bond to the leaving group is broken. The two potential energy diagrams shown below illustrate the two mechanisms. SN1 reaction SN2 reaction (transition state 1) Nu-R-X (transition state) (transition state 2) (carbocation intermediate Nu R-X (starting materials) Nu + R-x (starting materials) Nu-R+ Nu-R (products (products reaction coordinate reaction coordinate Your Final Lab Practical will be to develop and test a hypothesis of your own design exploring the nature of SN1 and/or SN2 reactions. You can discuss your ideas with others, but the hypothesis and experimental design must be your own work. You will the simple procedures for measuring SN1 and Sy2 reaction kinetics that you previously used (described below) and you can of course modify them to fit you hypothesis. A variety of alkyl halides will be made available for you to explore the chemistry; note that some of those listed are currently on order. Use them (or suggest others) to develop three separate hypotheses that you would test experimentally; include the specific experiments that you will run to test your hypotheses. Send those to your TA as soon as possible, but no later than Tuesday, November 24. TA will determine which among your proposals you are permitted to test starting Tuesday, December 1. You will be graded on safety, the novelty of your postulate, your experimental design, the results obtained, and your discussion of the results. Kinetics experiments should be the average of two or more experiments to ensure consistent and reproducible results. You may request additional chemicals to carry out your experiment, but we cannot guarantee their availability. Your proposed hypotheses should be submitted in the following format. Be creative and have fun! I. Clear statement of the hypothesis or postulate to be tested. (State exactly what you will test, not just what you want to do.)

Explanation / Answer

For SN2 reaction,

Test 1 : First set of reactants,

Substrate : 1-chlorobutane

Nucleophile : NaOH (aq)

Solvent : methanol

Test 2 : Second set of reactants

Substrate : 1-bromobutane

Nucleophile : NaOH

Solvent : Methanol

In Test 1, Cl- is a weaker leaving group than test 2, bromo which is bigger in size and can stabilize its pair of electrons after departing from the substrate. The rate of reaction would thus be higher in test 2, as opposed to test 1.

Test 3 : Third set of reactants

Substrate : 2-chloro-2-methylpropane

nucleophile : NaOH

solvent : methanol

We have changed the substrate from primary to tertiary, the rate of reaction would drop instantly to minimu. In fact we do not expect to see any reaction under SN2 conditions due to steric hindrance.

For SN2 reaction,

Test 4 : First set of reactants,

Substrate : 1-chlorobutane

Nucleophile : NaSH (aq)

Solvent : methanol

Here we have changed the nulceophile to a better one SH-. Since the nulceophile is involved in the rate determining step, we would see an increase in the reaction rate in this case.

For SN1 reaction,

Test 1 : First set of reactants,

Substrate : 2-chloro-2-methylpropane

Nucleophile : NaOH (aq)

Solvent : water

Test 2 : substrate : 2-chloro-2-methylpropane

Nucleophile : NaOH

Solvent : 80% Methanol : 20% H2O

As we change the solvent from more polar water to a less polar higher percentage of methanol solvent, the stability of carbocation would be reduced in solution. More polar solvents stabilizes the carbocation formed. thus the rate of reaction would be lower for Test 2 as compared to Test 1.

Test 3 : First set of reactants,

Substrate : 2-chloro-2-methylpropane

Nucleophile : KI (aq)

Solvent : water

Here we have changed the nulceophile to a better one, however since the nulceophile is not involved in the rate determining step, we do not expect to see any changes in the rate of the reaction.

Test 4 : First set of reactants,

Substrate : 3-bromopropene

Nucleophile : NaOH (aq)

Solvent : water

An allylic carbocation is more stable due to resonance effect and thus the rate of reaction is expected to increase in this case.

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