Cation, spontaneous rearrangement

The isobutyl cation spontaneously rearranges to the tart-butyl cation by a hydride shift. Is the rearrangement exergonic or endergonic Draw what you think the transition state for the hydride shift might look like according to the Hammond postulate. 

The isobutyl cation spontaneously rearranges to the tert-butyl cation by a hydride shift ... 

Liposome-polycation-DNA (LPD) nanoparticles (1) are formed by spontaneous rearrangement of a lipid shell around a polycation-condensed bacterial plasmid DNA core to form a virus-like structure (2). The LPD complexes consist of liposomes that are either made of cationic (LPDI) or anionic (LPDII) lipids and are sometimes referred to as lipopolyplexes, a broader category that also includes other lipid-based vectors (2). 

All attempts of preparing the parent secondary dication (63), a t -tiicyclo(5.1.0.0 ) octa-2,6-diyl dication, were unsuccessful. The dication was originally anticipated to undergo the circumambulatory rearrangement, as in cyclopropylmethyl cation rearrangements However, it spontaneously rearranged into the thermodynamically more stable homotropylium cation (64). 

The reactive cyclopropylidene cyclopropylcarbinyl cation 37 was generated from the corresponding bromide and silver hexafluoroantimonate, and was reacted in situ with olefins such as cyclohexene to form the addition products (equation 33). On the other hand, under the same conditions, the isopropylidene cyclopropylcarbinyl cation 41 rearranged spontaneously by ring expansion (equation 34)71. 

The fate cS the contact ion pair [RH A 1 is critical to electrm-transfer oxidation. Oxidative efficimey is the highest with those organic donors diat yield unstable radical cations, such as hexamethyl(Dewar benzene), which und goes spontaneous rearrangement (equation 7). > ... 

FIGURE 9.4 Spontaneous rearrangement of primary propyl cation into secondary propyl cation in gas phase. 

Steric factors are often responsible for skeletal isomerization in ion-radical states. The simple example in Scheme 6.31 illustrates the effect of steric congestion on activation energy of this kind of isomerization and depicts the transition of 2,2,3,3-tetramethylmethylenecyclopropane into 1,1,2,2-tetramethyltrimethylenemethane cation-radical. The rearrangement is brought about by one-electron oxidation of the substrate and represents an entirely barrierless process. Interestingly, methylenecy-clopropane (bearing no methyl groups) is protected from such a spontaneous collapse by a barrier of 7.4 k J mol l (Bally et al. 2005). 

Phenols and naphthols are converted to chromans in a one-pot reaction with isoprene. The specific catalyst AgOTf promotes tandem alkylation, via a 1,4-addition, and cyclisation by O-C bond formation (Scheme 10). With other dienes, 2-naphthol preferentially forms dihydronaphthofurans <06JOC6705>. The Bi(OTf)3-catalysed [1,3] rearrangement of (4-substituted aryl) 3-methylbut-2-enyl ethers to 2-prenylphenols is spontaneously followed by a cationic cyclisation to chromans <06S3963>. 

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