A fifth compound was studied but not included in the table (see paragraph II) 1,1-dibromoethylbenzene. This compound gave only substitution products following an mechanism. Suggest why this compound would react preferably via SN1 mechanism and not SN2? Give structures to support your conclusion. TABLE I.Products from the bimolecular reactions in dry ethyl alcohol, with [KOH or NaOEt] ~ 0-2.(No olefin was formed in dry alcohol alone, at 55° or 25°.)Compound.1. Ph-CBr, Me2. Ph-CBrH-CH₂Br3. Ph-CBrHMe4. Ph-CH₂ CH₂ BrOlefinicproduct.a-BromostyreneStyreneStyreneCompound.Ph-CBrH CH₂BrPh-CBrH-CH₂NoneReaction.Substitution product.Acetophenone diethylacetalB-Bromo-a-phenyldiethyl ether (?)a-Phenyldiethyl etherB-Phenyldiethyl etherBothTABLE II.Details of the above bimolecular processes.[KOH or NaOEt] ~0-2; k₂ is expressed as g.-mol./1./sec.; σA,B = 5 x 10-8 cm.k₂ × 104.E (cals.). PZ x 10-12.16,85010.222,4001.701.460.04951.4722,60021,60021,000Obs.Olefin, %, at55°.045025°.086-619.391.1Calc.86-51-420-70-691.9 1.284-7P.5.30.6180.007190.3850.00521Substitution1 Olefin(SubstitutionOlefin0.1850.0739Ph-CH₂ CH₂Br1.900.0256* These values are only approximate because of uncertainty regarding the values of E (see p. 349).86*74*2.574 In the present investigation the displacement of bromine from four of the five (side-chainbrominated) mono- and di-bromoethylbenzenes in dry and in aqueous ethyl alcohol wasstudied. The fifth, ßß-dibromoethylbenzene, could not be prepared sufficiently pure forkinetic purposes from phenylacetaldehyde, and one attempt to obtain it from benzyl-magnesium bromide and bromoform yielded dibenzyl instead. The results for the fourcompounds can be briefly stated: (1) the unimolecular olefin reaction was never observed;(2) aa-dibromoethylbenzene underwent the unimolecular substitution reaction only; and(3) the other three compounds suffered bromine displacement by all the first three methods,resembling isopropyl bromide in this respect (Hughes, Ingold, and Shapiro, loc. cit.). How-ever, except ax-dibromoethylbenzene, only x-bromoethylbenzene displayed any largeproportion of the unimolecular displacement. The nature and proportions of the productsformed are shown in Table I, and the kinetic details of the two bimolecular processes inTable II.

The structure 1,1 di-bromoethyl benzene is shown below,SN1 mechanism is a two step mechanism in which first step include the formation of carbocation, and the second step include the attack of nucleophile of the carbocation.SN2 is a single step mechanism where the removal of leaving group and attack of nucleophile takes place simultaneously. In such kind of mechanism, electrophilic centre should be sterically less hindered and a backside attack should be possible.Lets now examine the suitable mechanism for the given compund.If 1,1-dibromoethylbenzene undergoes SN2 mechanism, since phenyl ring is connected to carbon bearing electrophilic centre, back side attack is not possible, thus it is not possible for a SN2 mechanism.In SN1 mechanism a carbocation will generated as follows,This is a benzyl carbo cation so is much stable due to the resonance possibility of positive charge of benzene ring. But at the same time, since another bromine, which is an electronegative atom is attached to the carbo cation site, it destabilises the positive charge due to its electron withdrawing character (So the yield must be poor at this site). So it is high chance that nucleophile attack at any of the delocalised site most probably at para-position (depends on incoming nucleophile) and then the regain of aromaticity by deprotonation.Given below is the resonance stabilised carbo cation formed after the removal of one bromine group.Anyway it is much sure that the mechanism will follow SN1 instead of SN2.1,1-dibromoethylbenzene will undergo SN1 mechanism.