CHEM 2261 Chapter : PracticeTest2v5key

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azuremammoth471

15 Mar 2019

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Multiple choice (5 points each, 55 points total). Circle the one correct answer to each problem: circle the strongest nucleophile. E: circle the alkyl halide that would react faster in a sn2 reaction. cyclohexyl chloride sec-butyl chloride tert-butyl chloride butyl chloride. C: circle the solvent that would make an sn1 reaction go faster. D: circle the alkyl halide that would react faster in a sn1 reaction. Ch(ch3)2: what is the correct iupac name of the following molecule: circle one, (e)-2-bromo-7,7-dichloro-4-isobutyl-5-isopropyl-2-methyl-4-octene, (e)-2-bromo-4-sec-butyl-7,7-dichloro-5-isopropyl-2-methyl-4-octene, (z)-2-bromo-7,7-dichloro-4-isobutyl-5-isopropyl-2-methyl-4-octene, (z)-2-bromo-4-sec-butyl-7,7-dichloro-5-isopropyl-2-methyl-4-octene, (e)-7-bromo-2,2-dichloro-5-isobutyl-4-isopropyl-7-methyl-4-octene, (z)-7-bromo-2,2-dichloro-5-isobutyl-4-isopropyl-7-methyl-4-octene. Cl: fill up the squares with the corresponding chirality (r or s) in the following compounds and determine the relationship between them. (11 points) Isomers: in the following newan projection draw the most stable conformation of. 2,2,7-trimethyloctane looking along c4-c5 draw the hydrogens (6 points) Ch2ch(ch3)2: predict the major product(s) or fill in the reagent(s) for the following reactions. If there is no reaction write nr. (6 points each, 30 points total)

Related Questions

When an alcohol (substrate) is placed in an excess equimolar amounts of chloride ions and bromide ions in acid media the corresponding alkyl halides are obtained. The ratio of the alkyl halides depends orn several factors: the nature of the substrate, the reaction conditions, the solvent and the mechanism of the reaction When tert-butanol is placed in the presence of excess equimolar amounts of chloride and bromide ions in aqueous acid experimental data indicates 45% tert-butyl chloride and 55% tert-butyl bromide is obtained. This outcome can be explained by the fact that the rate determining step of the reaction does not involve the nucleophile, and once the carbocation is formed it is equally available to each nucleophile On the other hand, when n-butanol is placed in the presence of excess equimolar amounts of chloride and bromide ions in aqueous acid experimental data indicates 16% of n-butyl chloride and 84% of n- butyl bromide is obtained. The difference in the outcome can be explained by the fact that the rate determining step of this reaction requires the presence of the nucleophile, and in aqueous media the small size chloride ion gets "trapped" in the aqueous solvent cage and the bromide ion therefore gets a better chance to attack the substrate. This point can be demonstrated by changing the solvent. When n-butanol is placed in the presence of excess equimolar amounts of chloride ions and bromide ions in acid dimethyl sulfoxide the experimental data provides an 84% n-butyl chloride and 16% n-butyl bromide as the outcome. or all three reactions (hint: account for the mole ratiosl). 2. Draw complete mechanisms for all three reactions 3. Calculate the theoretical yield for chlorides and bromides if each reation was started with 2.5 mL of the corresponding alcohol, using an aqueous acid media. Place your results in a data table format. Sample Theoretical g of chloride Theoretical g of bromide tert n- 4. Calculate the expected percentage yield of each halide if you obtained a total of 0.025 moles of tert- nd 0.022 moles of n-butyl halides, and your % composition corresponds to the values butyl halides a of refractive index indicated and using an aqueous acid media. (hint:complete the data table) Sample # | Refractive | Temp. | % a (RI) | %Br (RI) | Mass ci | Mass Br % Yield Index of mixture ! !Tert-butyl| 1.4042 In-butyl 11.43 11 | 25.7â 126.1â 5. What would be the expected refractive index for the reaction of n-butanol with an excess of equimolar amounts of chloride and bromide ions if the reaction took place in dimethyl sulfoxide? No need to do calculations for the third reaction, just the first two.

Nucleophilic Substitution â Synthesis of an Alkyl Halide

Introduction

Alkyl halides can be prepared from alcohols by reactions with hydrogen halides (HCl, HBr, or HI) via nucleophilic substitution. In this type of reaction, the nucleophile displaces a leaving group from a carbon atom of an organic substrate (here the alcohol once protonated). Both electrons of the new bond to the carbon are provided by the nucleophile while the leaving group departs with both electrons of its bond to the substrate. There are two limiting mechanisms that are most common in describing nucleophilic substitution reactions at sp3 carbon centres : (1) a direct displacement (SN2) process and (2) a process that generates an intermediate carbocation (SN1). Which mechanism is a better description depends on the structure of the molecule containing the leaving group, the nature of the leaving group, the size of the nucleophile, and the polarity of the solvent. This experiment is a near-perfect example of an SN1 substitution. H3C OH CH3 H3C + HCl H3C Cl CH3 H3C + H2O (Equation 1) In this reaction, you will prepare 2-chloro-2-methylpropane (t-butyl chloride) from 2- methyl-2-propanol (t-butyl alcohol) using HCl as the strong acid and chloride source. Note that HCl first activates the alcohol in an acid/base reaction before the SN1 reaction proceeds. The final product is characterized by its yield, boiling point, and density. The presence of a halide atom is confirmed with a silver nitrate test.

1) State which of the electrophiles given below will react preferentially by i) SN1, ii) by SN2, or iii) capable of reacting by either of the two mechanisms depending on the given conditions. How can you affect those conditions to favour SN1 or SN2? Reason your predictions based on the structures of the compounds. Br-CH3, Br-CH2CH3, Br-CH(CH3)2, Br-C(CH3)3, Br-CH2-C5H6; C5H6 = phenyl

2) Rank the nucleophiles given below based on high, mediocre, and low nucleophilicity and reason why based on their structures. HO-CH3, H2N-CH3, KO-CH3, KO-C(CH3)3

3) Name two solvents that are commonly used for SN2 reactions. because they considerably slow down SN1 reactions.

4) Can you ever have only SN2 or only SN1?

5) Iodine is a better leaving group than bromine. But iodine is a better nucleophile than bromine. Why is that?

6) Using orbitals, draw the transition state of the SN2 reaction between sodium cyanide and bromomethane. Which orbitals are interacting with which? Why is the bond breaking? Why is the orientation important? Is there another angle besides backside attack that could theoretically work based on orbital geometry? Why doesnât this happen?

7) Name four reagents you can use to dry solvent. Why do we use magnesium sulfate in this lab instead of them?

8) Draw a mechanism with all the proper arrows for the reaction from this experiment.

9) What are we removing with the water wash? Why donât we just add the sodium bicarbonate directly to the reaction mixture instead of doing a water wash?