Tcrt-Butyl cation

Step 3 Capture of tcrt-butyl cation by chloride ion ... 

The major difference between the two mechanisms is the second step. The second step in the reaction of tcrt-butyl alcohol with hydrogen chloride is the unimolecular dissociation of tcrt-butyloxonium ion to tcrt-butyl cation and water. Heptyloxonium ion, however, instead of dissociating to an unstable primar y car bocation, reacts differently. It is attacked by bromide ion, which acts as a nucleophile. We can represent the transition state for this step as ... 

Computed values at the MP2/6-311G(d,p) level for the hydride exchange between tert-butyl and bicyclo[3.3.2]decyl cations and anchored to the experimental data for tcrt-butyl cation and iio-butane. Entropy values are symmetry-corrected at the HF/6-3 lG(d) level. 

Erom the standard Gibbs energy change for the chloride exchange between tcrt-butyl and bicyclo[2.2.2]octyl cations as determined from DPA results and the appropriate leaving group corrections (at the FlP/6-31G(d) level). Entropy corrections at the HF/6-31G(d) level. Ancillary experimental data for the other species are from Tables 1 and 3. 

For the unsubstituted pyridinium cation, reaction at the 2- and at the 4-position is predicted according to the theory. Indeed, reaction of protonated pyridine with the tcrt-butyl radical at low conversions (<30%) afforded selectively the ortho- and para-substituted derivatives without any alkylation at the meta position [16], It turned out that the ortho-para ratio is highly solvent dependent. If the reaction is conducted in H2O, the para product is formed as the major compound (see 10, ortho. para — 23 77). The same reaction in benzene afforded mainly the ortho compound [ortho-.para = 11 29). The reversal of the selectivity can be explained by assuming a reversible initial radical addition, especially if the reaction is conducted in H2O [16]. Similar results were obtained for the reaction with the tetrahydrofuryl radical [16]. The alkylations are generally stopped at low conversions. Since the alkylated pyridinium cations are only slightly less electrophilic than the starting pyridinium cations, overalkylation competes at higher conversion. For example, ethylation of the pyridinium cation at 100% conversion afforded a mixture of mono-, double- and tri-ethylated pyridinium salts (—> 11a e) [17]. 

In a similar study, cationic polymerization was transformed to AM polymerization for synthesis of PVA-b-PCL. For this purpose, tcrt-butyl vinyl ether (tBVE) was polymerized by HCl Et20 yielding living PtBVE, which was reduced to hydroxyl-terminated PtBVE. Subsequently, PTtVE-b-PCL was obtained using the hydroxyl-terminated polymer in AM polymerization of CL and converted to PVA-li-PCL by acid hydrolysis of the ether groups (Scheme 62). 

Some alkali-cation extraction results are known on the related molecule to (3) bearing tcrt-butyl groups on the para position of the phenyl rings [4]. We decided to model the binding properties of calixarene (3) toward these cations in order to see, first, the geometric modification when adding cations and, second, to know if... 

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