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SN2 lesson

First slide, at the bottom is a polymer change of poyl vinylidene chloride which can be viewed (along with PVC as an alkyl chloride)

Some introduction to alkyl halides, it is important to note that while alkyl halides are often thought of as man made there are plenty of examples from nature.

SN2 chemistry appears all over the organic chemistry. Also by understanding the SN2 reaction it will help you understand a lot of other reactions

What is a nucleophile, this is something important for you to learn. Nucleophiles will appear in many reactions. Also by understanding nucleophiles you will understand electrophiles.

Leaving groups are important, be careful of both thermodynamic and kinetic effects

This mechanism is important, by understanding the SN2 reaction you will help yourself with many other reactions in organic chemistry

Key thing to remember is backside attack

Get out the pop corn and sit back and watch the film.

Different alkyl groups, look at the different sizes of them.

A problem for students to do. By the way thiophenol smells just like burning car tyre rubber.

Some problems for you to do, try to predict what will happen in each case.

What happened, also what happens when we react the amino acid with the acid chloride and alkyl bromide. NB. DNF is a nasty solvent it is an equal oppitunitys nasty. It causes birth defects when women are exposed and it causes testical cancer in men.

A problem for the students to do at home.

Part of the synthesis of a drug, note that the ester group gives special reactivity to the alkyl bromide. Note the details of the early version of tear gas which the paris police used.

Something for next time

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2 Responses

  1. Thank you for providing such an excellent lesson on SN2 reactions.

    Can you please explain the problems you have given there?
    I couldn’t figure out the thiophenol problem, I also cannot digest how you chose the chlorine atoms that had to be substituted in the problem with PhSNa reagent(PhS- nucleophile).
    Please explain the problem in slide151(with 1,2-dihydroxybenzene) too.

    • The pentachloro compound (it is based on a natural chloro bromo compound from a marine organism) has one primary chloride, two secondary chlorides, a tertiary chloride and a vinyl chloide.

      The vinyl chloride is almost totally inert against a nucleophile such as thiolphenolate so we can ignore this one.

      If we react the alkyl halide groups under SN2 conditions then the primary one will react fastest due to steric reasons. Then the next two fastest ones will be the secondary alkyl chlorides and then the slowest one will be the tertiary one. The tertiary one will react so slowly that it will be close to impossible to observe any reaction.

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