Question

SN2 Pre-lab questions

1. Note that the general mechanism for an SN2 reaction involves stereochemistry. What happens to the substrate’s stereochemistry during an SN2 reaction?


2. How might steric hinderance in the substrates play a role in stabilizing or destabilizing the transition state? (hint: sp2 hybridized carbons sterically prevent nucleophilic attack.) How readily do you predict the reactants in our experiment will react in the SN2 reaction? Form a table for the SN2 reactions described in Today’s Experiment below, consisting of a column for your predictions (you can use + and – for reaction/no reaction) and an empty column for your results when you get them. Your results should include details such as how long it took before precipitate formed.

3. The rate-determining step also involves the nucleophile. What is the nucleophile in the given SN2 reactions? Why does this nucleophile favor an SN2 reaction?

4. Polar aprotic solvents favor SN2 reactions. Why is acetone considered a “polar aprotic” solvent?

Note: please dont write it in the paper, and take a picture of it. would you type it down. Thank you so much.

Answer 1

1) In case of SN2 reaction, the rate of reaction depends on both the reactant and incoming nucleophile.Here the nucleophile will come and attack at the backside of the reactant, so the final product has inversion of configuration. Stereochemistry of product is opposite to that of reactant streochemistry.

2) Generally primary alkylhalides undergoes SN2 reaction, These have sp3 hybridized carbon atoms.Here leaving group is not ready to loose itself, so that a strong nucleophile will needed to remove by attack on backside.Bulky groups will prevent from the back side attack.so that only primary alkylhalides will involve in SN2 reaction.

3) The rate determining step of SN2 involves both reactant and nucleophile. It is a single step mechanism.During the transition state, neucelophile will ready form bond and leaving group is ready to leave from the compound.

4) Generally polar aprotic solvents will favour SN2 reaction.Acetone is polar in nature due to having the dipole polarity but it is not a protic solvent, as it is not giving any protons.