# Exercises

Instruction

Fig.1

Instruction

Fig.2

Exercise

What are the characteristics of a good leaving group (nucleofuge), and what is the difference between a leaving group and a nucleophile?

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 Frequently, the leaving group in a nucleophilic substitution is, like the nucleophile, positively charged. No, sorry. Frequently, the leaving group in a nucleophilic substitution is, like the electrophile, negatively charged. Sorry, that is wrong. Frequently, the leaving group in a nucleophilic substitution is, like the electrophile, positively charged. Sorry, that is not correct. Frequently, the leaving group in a nucleophilic substitution is, like the nucleophile, negatively charged. Yes, that is correct! Frequently, the leaving group in an electrophilic substitution is, like the nucleophile, negatively charged. No, sorry.
Exercise

The leaving group (nucleofuge) and the nucleophile basically display the same chemical characteristics. So why does the nucleophile enter the substrate, while the nucleofuge leaves it?

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 The leaving ability of the leaving group is correlated to its ability to stabilize the positive charge. Sorry, that is wrong. The leaving ability of the leaving group is correlated to its ability to destabilize the negative charge. Sorry, that is not correct. The leaving ability of the leaving group is correlated to its ability to destabilize the positive charge. No, sorry. The leaving ability of the leaving group is correlated to its ability to stabilize the negative charge. Correct!
Exercise

If the nucleofuge in an $SN2$ reaction is a weak base, it is a ...

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 ... poor leaving group. No, sorry. ... good leaving group. Correct! ... rapid leaving group. Sorry, that is not correct. ... slow leaving group. No, sorry.
Exercise

Which of the halide anions has the best leaving ability?

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 $F−$ No. $F−$ is the worst leaving group of the halide anions. $Cl−$ Sorry. $Cl−$ is the second worst leaving group of the halide anions. $Br−$ No, sorry. $Br−$ is only the second best leaving group of the halide anioins. $I−$ Correct. $I−$ is the best leaving group of the halide anions. $At−$ No. Due to its radioactive instability, $At−$ has no practical importance in organic chemistry.
Exercise

Aside from halide ions, some derivatives of sulfonic acid are also very good leaving groups. These sulfonic acid derivatives are particularly good leaving groups, because they possess substituents that considerably ...

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 ... destabilize the negative charge by resonance destabilization. No, sorry. ... stabilize the positive charge by resonance stabilization. Sorry, that is wrong. ... stabilize the negative charge by resonance stabilization. Correct! ... destabilize the positive charge by resonance destabilization. Sorry, that is not correct. ... stabilize the negative charge by concordance stabilization. Sorry, that is wrong. What ought "concordance stabilization" to be?
Exercise

The hydroxide anion $OH−$ is a particularly poor leaving group, as its negative charge cannot be stabilized. However, a hydroxy group may be substituted if it has been previously chemically altered. How is this done?

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 Conversion to the better leaving group hydronium ion by protonation. Esterification by a sulfonic acid derivative, such as trifluoromethanesulfonic acid or methanesulfonic acid. Esterification by a hydrohalic acid derivative, such as hydrobromic acid or hydrochloric acid. Conversion to the better leaving group water by protonation.