Reações E2 e SN2 em Química Orgânica

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CHAPTER 7 219
 
(g) The reagent is tert-butoxide, which is both a strong 
base and a strong nucleophile. The substrate is tertiary 
so we expect only E2 (no SN2). The substrate has three  
positions that bear protons, but two of them are identical, 
giving rise to two possible regiochemical outcomes for 
the E2 process. Since the base (tert-butoxide) is 
sterically hindered, we expect that the major product will 
be the less-substituted alkene, and the minor product will 
be the more-substituted alkene. The latter is formed as a 
mixture of cis and trans stereoisomers, giving a total of 
three products, shown here: 
 
 
 
(h) The reagent is methoxide, which is both a strong base 
and a strong nucleophile. The substrate is tertiary so we 
expect only E2 (no SN2). The substrate has three  
positions that bear protons, but two of them are identical, 
giving rise to two possible regiochemical outcomes. 
Since the base (methoxide) is not sterically hindered, we 
expect that the major product will be the more-
substituted alkene (specifically, the E isomer, because 
the process is stereoselective). The minor products 
include the Z isomer, as well as the less-substituted 
alkene: 
 
 
 
(i) The reagent is hydroxide, which is both a strong base 
and a strong nucleophile. The substrate is secondary so 
we expect both E2 and SN2 processes, although E2 will 
be responsible for the major product. Accordingly, the 
major product is the more substituted alkene, with the 
trans configuration (because the reaction is 
stereoselective, favoring the trans isomer over the cis 
isomer). The minor products include the cis isomer, as 
well as the less-substituted alkene and the SN2 product 
(which is formed via inversion of configuration): 
 
(j) Treatment of an alcohol with concentrated sulfuric 
acid gives an E1 process to afford an alkene (or a 
mixture of alkenes). In this case, there are two different 
 positions that bear protons, so there are two possible 
regiochemical outcomes. The more-substituted alkene is 
the major product, and the less-substituted alkene is a 
minor product. Another minor product can result if the 
initially formed secondary carbocation undergoes a 
rearrangement to give a tertiary carbocation, followed by 
deprotonation to give a disubstituted alkene, shown 
below: 
 
 
 
(k) The reagent is chloride, which functions as a 
nucleophile, so we expect a substitution reaction. The 
substrate is secondary and the solvent is polar aprotic, 
indicating an SN2 process. As such, we expect inversion 
of configuration, as shown: 
 
 
 
7.77. 
(a) The reagent is HSˉ, which is a strong nucleophile, 
and the substrate is secondary, so we expect an SN2 
process, with inversion of configuration: 
 
 
 
(b) The reagent is DBN, which is a strong base, so we 
expect an E2 process. There is only one  position, so 
only one regiochemical outcome is possible. 
 
 
 
(c) The reagent is hydroxide, which is both a strong base 
and a strong nucleophile. The substrate is tertiary, so we 
expect an E2 process. There are three  positions, but 
two of them are identical, so there are two possible 
regiochemical outcomes. The more-substituted alkene 
is the major product, as shown. 
 
 
 
(d) The reagent is water, which is both a weak base and 
a weak nucleophile. The substrate is tertiary, so we 
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