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.
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.
Chemistry
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Author:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
Publisher:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
Chapter1: Chemical Foundations
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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, Me
2. Ph-CBrH-CH₂Br
3. Ph-CBrHMe
4. Ph-CH₂ CH₂ Br
Olefinic
product.
a-Bromostyrene
Styrene
Styrene
Compound.
Ph-CBrH CH₂Br
Ph-CBrH-CH₂
None
Reaction.
Substitution product.
Acetophenone diethylacetal
B-Bromo-a-phenyldiethyl ether (?)
a-Phenyldiethyl ether
B-Phenyldiethyl ether
Both
TABLE 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.
16,850
10.2
22,400
1.70
1.46
0.0495
1.47
22,600
21,600
21,000
Obs.
Olefin, %, at
55°.
0
450
25°.
0
86-6
19.3
91.1
Calc.
86-51-4
20-70-6
91.9 1.2
84-7
P.
5.3
0.618
0.00719
0.385
0.00521
Substitution
1 Olefin
(Substitution
Olefin
0.185
0.0739
Ph-CH₂ CH₂Br
1.90
0.0256
* These values are only approximate because of uncertainty regarding the values of E (see p. 349).
86*
74*
2.5
74](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2F194eaa6d-3d06-4caa-95b4-50a91c051936%2Ffef5c42f-fe2d-4792-98bc-887cbb8b3d64%2F4b2kpis_processed.jpeg&w=3840&q=75)
Transcribed Image Text: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, Me
2. Ph-CBrH-CH₂Br
3. Ph-CBrHMe
4. Ph-CH₂ CH₂ Br
Olefinic
product.
a-Bromostyrene
Styrene
Styrene
Compound.
Ph-CBrH CH₂Br
Ph-CBrH-CH₂
None
Reaction.
Substitution product.
Acetophenone diethylacetal
B-Bromo-a-phenyldiethyl ether (?)
a-Phenyldiethyl ether
B-Phenyldiethyl ether
Both
TABLE 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.
16,850
10.2
22,400
1.70
1.46
0.0495
1.47
22,600
21,600
21,000
Obs.
Olefin, %, at
55°.
0
450
25°.
0
86-6
19.3
91.1
Calc.
86-51-4
20-70-6
91.9 1.2
84-7
P.
5.3
0.618
0.00719
0.385
0.00521
Substitution
1 Olefin
(Substitution
Olefin
0.185
0.0739
Ph-CH₂ CH₂Br
1.90
0.0256
* These values are only approximate because of uncertainty regarding the values of E (see p. 349).
86*
74*
2.5
74
Transcribed Image Text:In the present investigation the displacement of bromine from four of the five (side-chain
brominated) mono- and di-bromoethylbenzenes in dry and in aqueous ethyl alcohol was
studied. The fifth, ßß-dibromoethylbenzene, could not be prepared sufficiently pure for
kinetic purposes from phenylacetaldehyde, and one attempt to obtain it from benzyl-
magnesium bromide and bromoform yielded dibenzyl instead. The results for the four
compounds 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 large
proportion of the unimolecular displacement. The nature and proportions of the products
formed are shown in Table I, and the kinetic details of the two bimolecular processes in
Table II.
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