CHE 201 Lecture Notes - Lecture 9: Leaving Group, Diethyl Ether, Molar Concentration

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coralwhale510

7 Oct 2018

School

University at Buffalo

Department

Chemistry

Course

CHE 201

Professor

Susan Bratcher

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Document Summary

In this experiment, we will perform a sn1 reaction involving 2-methyl-2-butanol using various chemicals such as hydrogen chloride, sodium sulfate, and saturated sodium chloride solution. These solutions were added to synthesize an organic liquid of pure 2-choloro-2-methylbutane. Two layers existed in the centrifuge tube, and the bottom layer is the organic layer. The organic layer is extracted and combined with nahco3. The sodium sulfate is added to dehydrate the solution, then we weigh it and calculate the percent yield. Last, this alkyl halide is put to the silver nitrate test, which resulted in a white precipitate indicating that reaction has occurred between the alkyl halide and silver nitrate. Alkyl halides are formed by a reaction involving alcohols and h-x acids. In an sn1reaction between an alcohol and a hydrogen halides, the alcohol is always protonated. In this experiment, we will form an alkyl halide from a tertiary alcohol. We are synthesizing 2-methyl-2-butanol to convert it to 2-chloro-2-methyl butane.

Related Questions

Questions:

1) In the tests with sodium iodide in acetone and silver nitrate in ethanol, why should 2-bromobutane react faster than 2-chlorobutane?

2) Why is benzyl chloride reactive in both tests, whereas bromobenzene is unreactive?

3) When benzyl chloride is treated with sodium iodide in acetone, it reacts much faster than 1-chlorobutane, even though both compounds are primary alkyl chlorides. Explain this rate difference.

4) 2-Chlorobutane reacts much more slowly than 2-chloro-2-methylpropane in the silver nitrate test. Explain this difference in reactivity.

5) Bromocyclopentane is more reactive than bromocyclohexane when heated with sodium iodide in acetone. Explain this difference in reactivity.

CHEM 211 Biological Chemistry Lab #8-Factors effecting the reactions of alkylhalides A. Experimental objectives Examine the effects of leaving group, alkyl group structure and solvent polarity on the reaction of alkyl halides Examine the effects of solvent polarity on the reaction of a tertiary alkyl halide with sodium hydroxide To examine SN1 and SN2 reaction conditions To learn the most two important factors that effects the reactivities of alkyl halides in nucleophilic substitution reaction B. Introduction The reactivities of alkyl halides in nucleophilic substitution reactions depend on two important factors: reaction conditions and substrate structure. The reactivities of the several substrate types will be examined under both SN1 and SN2 reaction conditions in this experiment A reagent composed of sodium iodide or potassium iodide dissolved in acetone is useful in classifying alkyl halides according to their reactivity in an SN2 reaction. Iodide is an excellent nucleophile, and acetone is a nonpolar solvent. Thetendency to form a precipitate increases the completeness of the reaction. Sodiumiodide and potassium iodide are soluble in acetone, but the corresponding bromidesand chlorides are not soluble. Consequently, as bromide ion or chloride ion is produced, the ion is precipitated from the solution. According to LeChatelier' s Principle, the precipitation of a product from the reaction solution drives the equilibrium toward the right such is the case in the reaction described here R-Cl Na RI NaCl (s) R-Br Na RI-NaBr (s) A reagent composed of silver nitrate dissolved in ethanol is useful in classifying alkyl halides according to their reactivity in an SN1 reaction. Nitrate ion is a poor nucleophile and ethanol is a moderately powerful ionizing solvent. The silver ion, because of its ability to coordinate the leaving halide ion to form a silver halide precipitate ,greatly assists the ionization of the alkyl halide. Again a precipitate as one of the reaction products also enhances the reaction C2H5OH R OC2H5 CI Ag AgCl (s) Page 1 of 5

3-Chlorobutane, 4-chlorobutane, allyl chloride, 2-chloro-2-methylpropane, 1-chloro-2-methylpropane, 2-bromobutane

a) Which alkyl halides were the most reactive under SN2 conditions? Which were the least reactive? Explain the order of reactivity under SN2 conditions by considering alkyl halide structure, nature of the leaving group, temperature, solvent, etc. Does the experimentally determined order fit what you predicted? Account for any anomalous observations.

b) Which alkyl halides were the most reactive under SN1 conditions? Which were the least reactive? Explain the order of reactivity under SN1 conditions by considering alkyl halide structure, nature of the leaving group, temperature, solvent, etc. Does the experimentally determined order fit what you predicted? Account for any anomalous observations.

Post Lab Questions

(1) Two of your six alkyl halides cannot react via an SN1 mechanism. Which are they? Why are they unreactive under SN1 conditions?

(2) One of your six alkyl halides reacts rapidly via both SN1 and SN2 mechanisms. Which is it, and why is it reactive under both mechanisms?

(3) One of your six alkyl halides is essentially unreactive via either SN1 or SN2 mechanisms. Which is it, and why is it unreactive?

(4) Explain why we used acetone as solvent for the SN2 reactions, and ethanol as solvent for the SN1 reactions.

(5) Allyl chloride is carcinogenic, as you determined in the prelab. Carcinogenic alkylating agents react with DNA bases such as cytosine (below), causing a change in the base structure, DNA mismatches and mutations which can lead to cancer. Draw a plausible reaction of allyl chloride with cytosine, and based on your results from this experiment, explain why allyl chloride is carcinogenic but 2- chlorobutane is not.

Follow up 1,2 and 3

CHE 201 Lecture Notes - Lecture 9: Leaving Group, Diethyl Ether, Molar Concentration

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