In: Chemistry
LAB 7: ELIMINATION OF ALKYL HALIDES
In Chem 223/237, you learned how to synthesize alkenes by eliminating alkyl halides. However, there is a great deal of complexity in the elimination reaction. Is the elimination E1, E2, or E1cB? Does the elimination compete with substitution? Does the elimination give a mixture of alkene isomers? This experiment will help to analyze how the choice of base can influence these answers. You will react 2-bromoheptane with either sodium methoxide or potassium tert-butoxide. Both are strong bases, so the E2 reaction should dominate over E1, and since your alkyl halide doesn’t contain a carbonyl group the E1cB reaction should not be relevant. In addition to the SN2 product, which is an ether, you may form 1-heptene, cis-2-heptene, or trans-2-heptene. You will analyze the product using GC-MS.
1) (2 pts) Why must the potassium tert-butoxide be weighed out as quickly as possible?
Your answer should include both a chemical reason, and an explanation of how that will impact your results.
(3 pts) You will purify your reaction using an extraction. Below, sketch the test tube, indicating all components of each layer (including solvents, reactants, products, etc.)
However, there is a great deal of complexity in the elimination reaction. Is the elimination E1, E2, or E1cB?
Yes there is great domination between E1, E2, or E1cB. But It depends the alkyl halide, Base used for the reaction and reaction condition.
Does the elimination compete with substitution?
Yes. There will be competition between elimination versus substitution. It depends the alkyl halide, Base used for the reaction.
Does the elimination give a mixture of alkene isomers?
Sometimes elimination will result in the mixture of alkene isomers depends on the precursor.
2-bromoheptane can undergo elimination as well substituion depending on what base is used. sodium methoxide or potassium tert-butoxide are strong bases which preferably goes elimination reaction than substitution.
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