Tert-Butyl carbocation

This linear correlation was then assumed to hold for the formation and reaction of aliphatic tertiary carbocations, and values of = 3.5 and 1.6 X 10 s for addition of 50 50 (v/v) water/trifluoroethanol to 5+ and the tert-butyl carbocation, respectively, were estimated from the values of fcobsd for reaction of the corresponding tertiary aliphatic chlorides using Eq. 2. ... 

Trimers may be formed through the addition of a tert-butyl carbocation to 2 or via addition of carbocation 1 to isobutylene. The trimer fraction mainly consists of 4-methylene-2,2,6,6-tetramethylheptane and 2,2,4,6,6-pentamethyl-3-heptene. 

Ethyl carbocation iso-Propyl carbocation tert-Butyl carbocation... 

The rearrangements of both the 1-butyl and 2-butyl carbocations to the tert-butyl carbocation occur rapidly in superacid solution. Both of these rearrangements proceed through several steps and must involve an unfavorable secondary carbocation to primary carbocation rearrangement. Show the steps in the rearrangement of the 1-butyl carbocation to the terf-butyl carbocation. 

The Focus On box in Chapter 8 on page 298 showed that when carbocations are generated in superacid solution, they undergo extensive rearrangements, usually forming a relatively stable tertiary carbocation. As an example, when 1-butanol is dissolved in superacid at — 60°C, the protonated alcohol is formed. Water does not leave at this temperature because the carbocation that would be formed is primary. When the temperature is raised to 0°C, water leaves but the carbocation rearranges rapidly to the more stable tert-butyl carbocation ... 

When the temperature is raised above 0°C, the absorptions for the protonated alcohol begin to decrease and a new signal Q begins to appear near 4 S (see Spectrum B). This is the absorption due to the te/7-butyl carbocation, in which all of the hydrogens are identical. No absorptions that could be attributed to other carbocations are observed, indicating that the rearrangement to the tert-butyl carbocation is very fast. 

The isobutyl carbocation, initially formed when l-chloro-2-methylpropane and AICI3 react, rearranges via a hydride shift to give the more stable tert-butyl carbocation, which can then alkylate benzene to form rert-butylbenzene. 

Phosphoric acid protonates 2-methylpropene, forming a tert-butyl carbocation. 

This is the synthesis of a somewhat controversial food preservative called BHT. It is an antioxidant that has been put in packaging to keep foods from becoming rancid from air oxidation. A balanced reaction would require two molecules of the alkene for each of the starting aromatic. The aromatic ring is relatively electron rich with two donors attached to it. With sulfuric acid present, the medium is definitely acidic. The first step is to generate the excellent electrophile needed for electrophilic aromatic substitution. For simplicity, let s symbolize sulfuric acid as H-A. The Markovnikov addition of a proton to isobutylene gives the tert-butyl carbocation, an excellent electrophile. 

When the reaction was halted at a fixed TOS of 3.0 h, the integrated product yields were higher compared to those obtained from the fresh catalyst, the maximum product yields declined only slightly per run, and the overall product quality inproved. Over 24 reaction cycles (see Table V), the TMP selectivity was relatively stable while dimethylhexane (DMH) selectivity decreased slightly. This provided an improvement in the TMP/DMH ratio from ca. 3.8 to ca. 5.0. This behavior, which was consistently observed, was mostly the result of higher product yields in the first hour of reaction likely due to the increased abundance of tert-butyl carbocations on the catalyst surface after regeneration. 

The first step is breaking the C-Cl bond, and this involves only the (CHslsC-Cl molecule. Then the hydroxide ion reacts with the tert-butyl carbocation in the second step. Since there is only one molecule in the slower first step (just assume that s true so we can illustrate this point), this is a unimolecular substitution reaction. 

Here the nucleophile (OH ) directly displaces the leaving group (Cl"), without forming a carbocation intermediate. This is because the methyl cation (CH3+) is much less stable than the tert-butyl carbocation formed in the previous question. 

Stoyanov, E. S., and Gomes, G. dos P. (2015). tert-Butyl Carbocation in Condensed Phases Stabilization via Hyperconjugation, Polarization, and Hydrogen Bonding. J. Phys. Chem. A, 119(32), 8619-8629. 

Therefore, we expect the transition state leading to the allyhc carbocation to be more stable than the transition state leading to the tert-butyl carbocation. 

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