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Chapter 14: Problem 303

Predict the order of reactivity of the following halides with (a) sodium iodide in acetone; (b) aqueous alcoholic silver nitrate:

Short Answer

Expert verified
(a) For sodium iodide in acetone, the order of reactivity is: RI > RBr > RCl > RF. (b) For aqueous alcoholic silver nitrate, the order of reactivity is: RF > RCl > RBr > RI.

Step by step solution

01

Identify the type of reaction

First, let's identify the types of reactions that take place with each reagent. Sodium iodide in acetone is a nucleophilic substitution reaction because it involves the iodide ion (I-) acting as a nucleophile that replaces the halogen atom in the halide. This reaction is known as an Finkelstein reaction. Aqueous alcoholic silver nitrate is also a nucleophilic substitution reaction, but here the silver ion (Ag+) reacts with the halide to form a precipitate of silver halide, and the nitrate ion (NO3-) replaces the halogen in the halide. The reaction can be used to test for halide ions; the appearance of a silver halide precipitate indicates that a reaction has occurred.
02

Analyze the factors affecting reactivity for (a) sodium iodide in acetone

For the Finkelstein reaction, the reactivity of halides with sodium iodide in acetone is determined by the stability of the leaving group. The more stable the leaving group, the more likely it is to leave, making the reaction proceed at a faster rate. In general, the stability of the leaving group increases as we go down the periodic table: I- > Br- > Cl- > F-. This trend can be attributed to the decreasing size and increasing polarizability of the halogen ions. Thus, in a Finkelstein reaction with sodium iodide in acetone, the order of reactivity is typically: RI > RBr > RCl > RF where R represents the rest of the molecule.
03

Analyze the factors affecting reactivity for (b) aqueous alcoholic silver nitrate

When reacting with aqueous alcoholic silver nitrate, the reactivity of halides is dependent on the stability of the silver halide precipitate formed during the reaction. The stability of the silver halide precipitate increases from F- to I-, as the following order: AgF < AgCl < AgBr < AgI This trend is due to the increasingly covalent nature of the bond between silver and the halide ion as we go down the periodic table. As a result, the order of reactivity of halides with aqueous alcoholic silver nitrate is: RF > RCl > RBr > RI
04

Provide the order of reactivity for each reagent

Based on our analysis of the factors affecting the reactivity of halides, we can predict the order of reactivity for each reagent as follows: (a) Sodium iodide in acetone: RI > RBr > RCl > RF (b) Aqueous alcoholic silver nitrate: RF > RCl > RBr > RI

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Most popular questions from this chapter

Outline a possible laboratory synthesis of each of the following compounds from alcohols and phenols: (a) methy1 tert-buty 1 ether (b) n-propy1 phenyl ether (c) cyclohexy1 methy1 ether

Using models, suggest explanations for the following: (a) On E2 elimination with \(\mathrm{t}-\mathrm{BuOK}^{-+} / \mathrm{t}-\mathrm{BuOH}\), both cis-and trans-2-phenylcyclopenty1 tosylates give 1 -phenylcyclo-pentene as the only alkene; the cis isomer reacts 14 times as fast as the trans. (b) On E2 elimination with \(\mathrm{n}-\mathrm{C}_{5} \mathrm{H}_{11} \mathrm{ON}^{-+} \mathrm{a} / \mathrm{n}-\mathrm{C}_{5} \mathrm{H}_{11} \mathrm{OH}\) to give 2-chloronorbornene, II reacts about 100 times as fast as its diastereomer, I.

An alternative mechanism for \(E_{2}\) elimination is the following: (a) Would this mechanism lead to a first-order kinetics with respect to the concentrations of \(\mathrm{OH}\) and ethy1 chloride? Explain. (b) This mechanism has been excluded for several halides by carrying out the reaction in deuterated solvents such as \(\mathrm{D}_{2} \mathrm{O}\) and \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OD}\). Explain how such experiments could be relevant to the reaction mechanism.

Consider the reaction of isopropyl iodide with various nucleophiles. For each pair, predict which will give the larger substitution/elimination ratio. (a) I or \(\mathrm{Cl}\) (b) \(\mathrm{N}\left(\mathrm{CH}_{3}\right)_{3}\) or \(\mathrm{P}\left(\mathrm{CH}_{3}\right)_{3}\) (c) \(\mathrm{CH}_{3} \mathrm{~S}^{-}\) or \(\mathrm{CH}_{3} \mathrm{O}^{-}\)

Predict the major products, if any, for the reaction of isobuty1 n-propyl ether with: (a) \(\mathrm{H}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}\), room temperature (b) Dilute, aqueous \(\mathrm{H}_{2} \mathrm{SO}_{4}\) (c) Hot, concentrated HBr.
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