1-Chlorobutane, 1-Bromobutane, Bromocyclopentane , Bromocyclohexane , 2- Chlorob

Question

1-Chlorobutane, 1-Bromobutane, Bromocyclopentane ,Bromocyclohexane ,

2- Chlorobutane , 2-Bromobutane, 2-Chloro-2-methylpropane, 2-Bromo-2-methylpropane

are placeed in Sn2 and Sn1 reaction. Anser the followings

1)List the alkyl halides in order of decreasing reactivity toward each of the reaction conditions. Briefly discuss why this order of reactivity was observed.

2) Order the reactivity of the primary halides to each reagent,briefly expalin

3) Order the reactivity of the secondary halides to each reagent. Briefly explain

4 ) Order the reactivity of the tertiary halided to each reagent.Briefly explain.

Explanation / Answer

1. SN1 : 2-Bromo-2-methylpropane > 2-Chloro-2-methylpropane > Bromocyclopentane > Bromocyclohexane > 2-Bromobutane > 2- Chlorobutane > 1-Bromobutane > 1-Chlorobutane

The above order is based on the following factors:

a. Tertiary > Secondary > Primary: Increase in induction effect leads to more polar bonds which break more easily in polar solution, hence rate is faster.

b. Size of halide ion: The larger the halide ion, the longer the bond which makes it weaker and more easy to break. Hence Br > Cl

c. Ring Strain / Steric Hindrance: Presence of this reduces chances of SN2 reaction occuring.

For SN2, the order is just reversed as the nucleophile attaches itself to the halide first and then halide ion detaches, thus the opposite is true for all three factors discussed above. Primary > Secondary > Tertiary, Smaller halide ion, so Cl > Br and less steric hindrance increase rate.

2. For SN1,

1 - Bromobutane > 1 - Chlorobutane due to size of Br > size of Cl, thus Br bond is weaker and more easily broken in polar solvent.

For SN2

1 - Chlorobutane > 1 - Bromobutane since size of Br makes it more difficult for nucleophile to approach the alkyl halide.

3. For SN1,

Bromocyclopentane > Bromocyclohexane > 2-Bromobutane > 2- Chlorobutane

Due to increase in ring strain, Br will be easily removed from the cyclic compounds. Size of Br > Size of Cl is why straight chain 2 - Bromobutane reacts faster than 2 - Chlorobutane.

For SN2, the order is reversed as the ring creates steric hindrance making it tough for the nucleophile to attach.

4. Tertiary follows the same pattern as primary with the bromo tertiary halide more reactive for SN1 and the chloro tertiary halide more reactive to SN2

Related Questions

Navigate

• Browse (All)
• Browse 1
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.