Title: Nucleophillic Substitution Reaction

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Nor Amirah Farhana Nawawi Organic Chemistry Lab Report Bo Shen

Title: Nucleophillic Substitution Reaction

Introduction: This lab experimented on the reactions of the chemicals that undergoes SN1 or SN2 reaction. Nine different compounds were given to be examined with two reagents - NaI in acetone and AgNO3 in ethanol. The SN1 reaction happens in AgNO3 in ethanol reagents, and SN2 reaction is in NaI in acetone.

Procedure: Following the lab manual.

Results:

compound

NaI /acetone (SN2)

AgNO3/ethanol (SN1)

Bromobenzene

NR

NR

Bromocyclopentane

X

2 sec

Bromocyclohexane

NR

4 sec

2-bromobutane

5 min

2 sec

2-chlorobutane

NR

X

Chloroacetone

7 sec

X

1-chlorobutane

X

X

t-butyl chloride

NR

6 sec

Benzyl chloride

3 min

X

Conclusions and discussion

Bromobenzene undergoes no reaction for both SN1 and SN2. This is because bromobenzene is very stable, and contains allylic and vinyllic bromine, which is also very stable, and cannot be a good nucleophile.

Bromocyclopentane reacts under SN1 and SN2, but it shows a faster reaction in AgNO3/ethanol reagent, that is SN1. This is because bromocyclopentane is secondary bromine, and have bigger steric strain, since it is a cyclic compound. The bigger steric in a molecule, the harder it is for the nucleophile to attack the leaving group (-Br) from the opposite sides, therefore, SN2 reaction is slower than SN1 for bromocyclopentane. From this reaction, precipitation occurs to give out AgBr in ethanol and NaBr in acetone.

Bromocyclohexane, on the other hand, shows no reaction in SN2 reagent, but almost an immediate reaction in SN1 reagent. The reasons are very much the same with bromocyclopentane above - steric strain. As bromocyclohexane is bigger than that of bromocyclopentane, the steric in bromocyclohexane is too much for the nucleophillic attack from the opposite side of the leaving Bromine. In the end, only SN1 reaction could pass this nucleophillic substitution.

2-bromobutane undergoes a slow SN2 reaction, but shows an immediate result in SN1 reaction. As 2-bromobutane consists of secondary bromine, both SN1 and SN2 could happen. The precipitate for this reaction should be NaBr and AgBr. On the other hand, 2-chlorobutane undergoes an even slower SN1 and SN2 reactions. This happens because bromine is a better leaving group than chlorine. Bromine is larger in diameter, and less electronegative, too; therefore making it easier to leave the alkyl group. The precipitate for this reaction is NaCl and AgCl.

The reaction of chloroacetone, by comparison is mainly SN2, because the reaction in SN1 is quite slow. As chloroacetone consists of primary chlorine, SN2 reaction is very favorable. Moreover, the stereochemistry of this compound helps the reaction go faster (nucleophile came through from the opposite of leaving group). The product for this reaction is the precipitate of NaCl.

1-chlorobutane is slow in reaction with both, either SN1 or SN2. 1-chlorobutane has primary chlorine; theoretically it is available only for SN2 reaction. But it also reacted in SN1 - only even slower. The reasoning is the same as the above; chlorine makes a hard-to-leave leaving group. The precipitates for 1-chlorobutane in both reagents are NaCl and AgCl.

For t-butyl chloride, no reaction occurred in SN2 reaction, but instant result appears in SN1 reaction. This is mainly because the leaving group, -Cl is a tertiary atom, making it only available for SN1 substitution. Furthermore, there is no carbocation rearrangement. The precipitate is AgCl.

Benzyl chloride reacts instantaneously with SN2 reagent and around several minutes in the other reagent, producing NaCl in the acetone solution and AgCl in the ethanol solution. Different from bromobenzene, benzyl chloride is consisted of a carbon in between the leaving group and the arene. This creates a partial charge, ( on the...
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