Question

In this exercise, you will use two reagent mixtures to test a variety of organic halides. The distinct differences in the factors affecting the S_N2 and S_N1 mechanisms make it possible to determine which mechanism is favored by a given compound. One reagent and solvent favors S_N2 reactivity, the other S_N1 reactivity. From the results of your tests, you will determine which mechanism, if either, is favored by a given compound. In your post-lab assignment, you will be required to explain or rationalize your results in terms of the electronic and/or steric factors involved for each compound.

The two test reagent mixtures you will be using are sodium iodide in acetone and silver nitrate in ethanol. Iodide is a very good nucleophile and acetone is a polar aprotic solvent; therefore, compounds which can react by an S_N2 mechanism should do so readily with this reagent. On the other hand, nitrate is a very poor nucleophile and ethanol is a polar protic solvent. Silver ion will coordinate very efficiently with any free halide, promoting the ionization of halohydrocarbons. Thus, the AgNO₃/ethanol reagent favors reactivity by the S_N1 mechanism.

	Reactant	KI/acetone	AgNO3/ethanol
1	bromobenzene
2	bromocyclopentane
3	bromocyclohexane
4	2-bromobutane
5	2-chlorobutane
6	1-chloropropan-2-one
7	1-chlorobutane
8	2-chloro-2-methylpropane
9	1-chloromethylbenzene

Please explain !

Answer 1

Ans: (Reactants | Reagent ! KI Acelone to promobenzene Since, Br is attached with an aromatic ring the structure does not allow the formation of Carbocation (20 phononiuun cation) so, it will not undergo Sul. Also, the back side attack is not possible because the C-Br bond has a partial double bond character due to electronic offeet (resonance). so, SN2 is also not observed for this compound ne b o by wha you like be 2. bromo eyelopenlane Br It will participate in this reaction through Suz pathway because its a Secondary halide and has a bigger amount of Sterie strain and angle Strain and out 3. bromo eyeloherane Since, 'It is a strong nudeophile in acelona medicine so, it attacks the compound at C-Br carbon from rare side and facilitates SN 2, reaction

4. 2-bromobuláne ni BO It will undergo SN2 reaction as it is a 2° alkyl halide it also has a tendeney co proceed through Sn', but in polar aprofic medium the carbocation is not oven Stabilized so, it will prefer to undergo Saiz pathevay. 5.2-chlorobulare en It also undergo sn2 reaction but at a much slower rale than 2-bromobulaire because da is poor leaving group than Bri Y d a nosila s 6. 1-chloro propan-2-one D S 94 proceed through Souza mechanism breause it produce unstable earbocalion c o ) which gets no Stability in acelone mediuen. So, backside aftack by the nucleophêla I is more favourable. ad he willen wohwasan 7 1-chlorobulăne Sinel, this struclure will experience relatively lower amount of Storic hindrania with the nucleophile, so the backside attack is effective and SNZ reaction is olasorved at a higher rale,

a 2-chloro-2-methylpropane st It will undergo Sul reaction This is a storically hinderd 30 alkyl halide so, the rare side attacke by the nucleophile is difficult. Rather its will experience a huge storic ropulsion at the transition stalo in SN2. So, SN2 mechanism is not favourable. On the other hand it will produce stable carbo- -cation with which facilitate SNI reaction. 9. I-chloromethyl benzone This compound will give roconance' stabilized Carbocation CH₂-ce so, it will preferably undergo SNI reaction. On the other hand the prosence of bully group a storie factor reduces the tendency og Sner for this compouns.