Cationic structures

FIGURE 5 8 Methyl migration in 1 2 2 tnmethylpropyl cation Structure (a) is the initial second ary carbocation structure (b) is the transition state for methyl migration and structure (c) is the final tertiary carbocation... 

Compare CCl distances in the reactants. If shorter bonds are stronger, which reactants will show unusual reactivity, and in what direction Compare the cation structures with each other and with the reactants. If the structural changes in reaction (1) are normal , then what unusual changes, if any, occur in reactions (2) and (3) ... 

Structures with a cyclic character (70° a 110°) are less solvated than open cation structures (a < 70° a > 110°) due to a larger charge delocalization in the former. Thus, the alterations of the potential energy surface described above are plausible. There are two possible structures for activated complexes in solution. They... 

A unimolecular ionization was shown to be the mechanism of solvolysis by means of rate studies, solvent effects, salt effects, and structural effects (179,180). The products of reaction consist of benzo [bjthiophen derivatives 209 or nucleophilic substitution products 210, depending upon the solvent system employed. By means of a series of elegant studies, Modena and co-workers have shown that the intermediate ion 208 can have either the open vinyl cation structure 208a or the cyclic thiirenium ion 208b, depending... 

In order to imderstand the effects of the cation structure in the transesterification between methanol and EC, quaternary ammonium chloride catalysts of different alkyl cations such as TPAC, TBAC, THAC, TOAC, and TDodAC were used at 140 C. Table 1 shows EC conversions after 1 h... 

In general, the stability of a PT catalyst is a function of cation structure, presence of anions, type of solvent, concentration, and temperature. Degradation of catalysts under PTC conditions may occur. For instance, ammonium and pho.sphonium salts may be subject to decomposition by internal displacement (usually at temperatures of 100 - 200 °C) ... 

Fig. 2 Cationic structure of 2. a Metal skeleton, b Structure of one of the faces of the octahedron, c View of the structure of one of vertices of the octahedron. Cu filled circle Ln circle with cross-hatching...

Fig. 4 Cationic structure of 4. a Stereo view of the structure of the octahedron with only two of the vertices, b Ellipsoid and c space-tilling representations of 4. d Huge LngCui2 octahedral core Emcapsulates a CIO anion, e f Coordination environment of Tb3+ and the outer Cu2+ ions in the two vertices. The symmetry codes of a and b are z, x — 1, y+ 1 and y + 1, z — 1, x, respectively. The dashed line represents the weak coordination bonding...

Allenyl cations 1 are a stabilized form of vinyl cations1-3 in which the /1-carbon atom of the vinylic structure is part of the substituent which effects the stabilization of the ion via its electron-donating ability. This leads to a resonance hybrid having formally the alkynyl cation structure 2. Allenyl cations should be distinguished from the allenyl substituted carbenium ions 3 formulated as the mesomeric structures of the vinyl cations 4 (dienyl cations) stabilized by an w-vinyl group (equation 1). 

Reactions between bis(alkinyl)dimethylplumbanes and trialkylboranes resulted in the cleavage of the lead-alkinyl bond and the fast intramolecular transfer of the alkinyl group to the boron atom forming the alkinylborate anion and the triorganolead cation (structure A) (Figure 49)154. 

The tert-butyl cation structure (7) with Cs symmetry is better suited for hyperconjugation than the C3h form and is thus energetically slightly favored.29 The energy surface for methyl-group rotation is however very flat. 

However, contrary to the parent cation, the corresponding isomeric cyclopropyl-methyl cation structures 58 and 59 are no minimum structures (MP2/6-31G(d)) and do not contribute to the averaged chemical shifts. 

Instead the allyl cation 97 was obtained. The reported experimental 13C NMR data (<513C(exp) 8 — 250/243, 153, 60 ppm) are in agreement with the cyclopentenyl cation structure 97, but differ significantly from the calculated 13C NMR chemical shift for both Jahn-Teller distorted valence isomeric cyclopentadienyl cation structures 95 and 96. 

Hydrocarbon radical cations, structure and reactivity of, 38, 87 Hydrocarbons, small-ring, gas-phase pyrolysis of, 4, 147... 

Figure 11. Optimized structure for cis- and trans-dimethyl 1,6-p-H-bridged 2-octyl cation structures 24 and 25 showing bond distances and bond angles.

Effect of cation structure on the kinetic stability of RNH,PF6 complexes of [28] in CDClj" 1 ... 

Uneven open shell Pn clusters are easier to ionize than even closed shell ones and the stability of the closed shell uneven P cluster cations is higher. For very large Pn+ cations with n = 25 + 8x (x — 0.1.2. 8) islands of stability were observed in the time of flight mass spectrum (TOF-MS) obtained by laser ablation of red phosphorus, suggesting that the more stable P clusters have connections with units of eight P atoms [71d]. A lot of effort has been put into the calculation of the most stable Pn+ cation structures. The respective global minimum structures of the more stable uneven P3+, Ps+, P71 and P<)h cluster cations are shown in Figure 2.6-10 [73, 74],... 

From published photoelectron data for these compounds we can infer that cations formed under these conditions will carry some excess internal energy. The photoelectron spectrum of borazine indicates no significant change in the structure of the cation relative to the precursor although a slight Jahn-Teller distortion is possible. The alternate cation structure... 

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