Why would it be bad to wash the test-tubes for the S_N2 conditions with water be
ID: 507060 • Letter: W
Question
Why would it be bad to wash the test-tubes for the S_N2 conditions with water before doing the test? (b) So related to the question above, what should you have used to wash the test tubes before doing the SN1 conditions? Explain. (c) We learned that 3 degree RX do not undergo SN_2 reactions. So why did you observe a reaction for some of these? (Can you provide an alternative scenario by which they react) (d) Would you see the results for the 3 degree RX slower or faster in the SN_2 reactions if you used something like CH_2Cl_2 or ether as the solvent? Explain. (e) Suppose we tried to do the SN-1 experiment with the cheaper NaNO_3. Would the experiment still work? For FOUR of the reactions on the next page, write the type of mechanism (S_N1 or S_N2) in the picnic basket on the left, and then draw the product(s) of the reaction on the right. Be sure to show stereochemistry where needed. Also please have at least one SN1 and one SN2 reaction, as well as one of the reactions with "1.0 equiv".Explanation / Answer
9.
(a) water is a polar protic solvent which promotes formation of carbocation intermediate as in Sn1 reaction. It solvates the nucleophile used for the Sn2 reaction and thus it is not available for reaction. Thus presence of water would reduce the rate of an Sn2 reaction. Hence washing of test tubes with water is not adviced.
(b) For an Sn1 reaction as discussed above, water is a good solvent and thus water may be used to wash test tubes prior to an Sn1 reaction.
(c) tertiary alkyl halides do not undergo an Sn2 reaction, however they do undergo an Sn1 reaction (to form substituted product) or in most of the cases an E1 elimination reaction to form an alkene as the end product.
(d) Both CH2Cl2 and ether are polar aprotic solvents and thus Sn2 reaction in these solvent would go faster for the tertiary alkyl halides.
(e) NaNO3 has NO3- as the strong nucleophile which promotes Sn2 reaction instead of an Sn1 reaction. The reaction would still work but at much lower rate.
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