Question

In each of the following indicate which reaction will occur faster. Explain your reasoning. (a) CH3CH2CH2CH2Br or CH3CH2CH2CH2I with sodium cyanide in dimethyl sulfoxide (b) 1-Chloro-2-methylbutane or 1-chloropentane with sodium iodide in acetone (c) Hexyl chloride or cyclohexyl chloride with sodium azide in aqueous ethanol (d) Solvolysis of 1-bromo-2,2-dimethylpropane or tert-butyl bromide in ethanol (e) Solvolysis of isobutyl bromide or sec-butyl bromide in aqueous formic acid (f) Reaction of 1-chlorobutane with sodium acetate in acetic acid or with sodium methoxide in methanol (g) Reaction of 1-chlorobutane with sodium azide or sodium p-toluenesulfonate in aqueous ethanol

Answer 1

The reactivity of the given reactions is determined by the stability of the leaving group on the alkyl halide and the nucleophile. The reaction with the alkyl halide that has a stronger leaving group or a more reactive nucleophile will occur faster.

Step-by-step explanation:

In each of the given reactions, the reactivity can be determined by considering the leaving group on the alkyl halide and the nucleophile. A good leaving group is one that can stabilize the negative charge that forms on it after it leaves. In general, the order of leaving group reactivity is I > Br > Cl > F. Therefore, in all of the given reactions, the reaction with the alkyl halide that has a stronger leaving group or a more reactive nucleophile will occur faster.

(a) CH₃CH₂CH₂CH₂I will react faster because iodine (I) is a better leaving group than bromine (Br).

(b) 1-Chloro-2-methylbutane will react faster because the longer carbon chain of 1-chloropentane leads to weaker C-Br bond strength.

(c) Cyclohexyl chloride will react faster because the ring strain in cyclohexane makes it a more reactive nucleophile than hexyl chloride.

(d) Solvolysis of tert-butyl bromide will occur faster because the formation of a tertiary carbocation is more stable than a secondary carbocation formed in the solvolysis of 1-bromo-2,2-dimethylpropane.

(e) Solvolysis of sec-butyl bromide will occur faster because the secondary carbocation formed is more stable than the primary carbocation formed in the solvolysis of isobutyl bromide.

(f) Reaction of 1-chlorobutane with sodium acetate in acetic acid will occur faster because acetate ion is a better nucleophile than methoxide ion.

(g) Reaction of 1-chlorobutane with sodium azide will occur faster because azide ion is a stronger nucleophile than p-toluenesulfonate ion.

Answer 2

A. Butyliodide will react faster than butylbromide, this is because iodide is a better leaving group in substitution reaction than bromide. B. 1-chloropentane is more reactive than 1-chloro2methylbutane, this is because Alkyl groups at the carbon atom decrease the reaction rate of SN2 reaction. C. Chloro- hexanechloride is more reactive than hexyl chloride because determining the rate of reaction in SN1 reaction of formation of carbocation is more stable than the primary one. SN1 reaction is a secondary carbocation reaction. D. Terri-butylbromide is more reactive than 1-bromo 2,2 dimethylpropane, this is because Tertiary carbocation is stable compared to the primary, this is because the rate of determining step involved in SN1 reaction. E. Sec-butyl bromide is more reactive than isobutylbromide, this is because Sec-butyl bromide belong to the secondary all halide why the other belongs to primary class. F. The reaction is faster in sodium methoxide in methanol than sodium acetate in acetic acid, this is because 1-chlorobutane is a primary alklyl- chloride than and the strength of nuclephile determines the rate of reaction. G. when sodium azide mixed with ethanol is used, the reaction will be faster, because strong acid form weak conjuage base and also azide is a better nuclephile.