Delocalization cations

So-called delocalized cationic azo dyes are another type ia which the positive charge is delocalized (or distributed) across the dye cation. Basic Blue 54 (132) (2-amiao-6-methoxybenzothiazole coupled to /V, /V-dimethy1 ani1 ine and then quarternized with dimethyl sulfate) is an example of this class which can also be considered as a diazamethine dye. 

Basic Red 22 (134), which contains 1 part ia 7 of the yellowish red 1,4-dimethyl isomer, Basic Red 29 (135), and Basic Yellow 25 (136) are all examples of delocalized cationic azo dyes. Dyes of this type can also be synthesized by Hbnig s oxidative coupling reaction of heteroaromatic hydrazones with tertiary aromatic amines. 

Display electrostatic potential maps for both bisected and perpendicular conformers of cyclopropylcarbinyl cation. For which is the charge more delocalized Is the more delocalized cation also the lower-energy cation ... 

One possible explanation is that adamantyl cation, an intermediate in the reaction, is particularly unstable because it cannot accomodate a planar carbocation center (see Chapter 1, Problem 9). Examine the geometry of adamantyl cation. Does it incorporate a planar carbocation center Compare electrostatic potential maps of adamantyl cation and 2-methyl-2-propyl cation. Which cation better delocalizes the positive charge Assuming that the more delocalized cation is also the more stable cation, would you expect adamantyl tosylate to react slower or faster than tcrf-butyl tosylate Calculate the energy of the reaction. 

Delocalized cations, represented by two or more resonance contributors, are usually more stable than localized cations. However, the fact that several resonance contributors can be drawn for a molecule does not guarantee that the molecule will actually be resonance stabilized (see also Chapter 12, Problem 10). 

The H and 13CNMR spectra of various cyclopentazepines have been recorded (Tables 1 and 2), as has the HNMR spectrum of 7V,7V-dimethylcyclopent[e]azepin-l-amine.68 A detailed analysis of geminal and long-range 13C-H coupling constants for cyclopent[c]azepine is also available.87 The HNMR spectra of 9//-pyrrolo[l,2-a]azepin-9-one (8b) and its fully delocalized cation have been recorded in various solvents.7... 

Benzodiazepines 1 are colorless, basic compounds which are highly susceptible to hydrolysis. They form stable, deeply colored salts 2 containing extensively delocalized cations. In stronger acids colorless diprotonated species 3 are produced. 

The range of structural alternatives explored by valency-deficient carbon species and the subtle interplay of substituents is remarkable. Scheme 7.6 (ORTEP adapted from reference 31) illustrates an example of an X-ray structure clearly describing a localized [C-H C+] carbenium ion (A) where a symmetric bridging structure [C-H-C] + (B) could have been assumed. In this case it is proposed that a charge-transfer interaction between the resonance delocalized cation and the adjacent electron-rich carbazol moiety may be responsible for the stabilization of the localized form over the three-center, two-electron (3c-2e) bridging structure. 

Reindl, B. Clark, T. Scheleyer, P. v. R. Modern molecular mechanics and ab initio calculations on benzylic and cyclic delocalized cations. J. Phys. Chem. A. 1998, 102, 8953-8963 and references therein. 

Formation of some mesoionic [ 1,3,4]rhiazolo[3,2-z/ [1,3,5]triazines 303 and related [l,2,4]triazolo[2,3- ][l,3,5]tri-azines 305 has been observed by Anders et al. <2005T673>, as shown in Scheme 60. These authors reported that the quaternary salts 302 and 304 containing polyfused delocalized cations easily react with amines to result in ring opening to 303 and 305, respectively. 

Delivery receipt, 25 330 Delocalized cationic azo dyes, 9 423 Delta-3-carene (A-3-carene), 24 499 8-alumina, 2 404, 406t Delta coke, 22 704 8-damascone, 24 570... 

Large, soft, sterically hindered and delocalized cations such as Ph4As+ and [Ph3P=N=PPli3]+ prefer to be associated with CC13 anions. 

Rate constants and products have been reported for solvolysis of benzhydryl chloride and /7-methoxybenzyl chloride in 2,2,2-trifluoroethanol (TFE)-water and-ethanol, along with additional kinetic data for solvolysis of r-butyl and other alkyl halides in 97% TFE and 97% hexafluoropropan-2-ol. The results are discussed in terms of solvent ionizing power Y and nucleophilicity N, and contributions from other solvation effects are considered. Comparisons with other 3 nI reactions show that the solvolyses of benzhydryl chloride in TFE mixtures are unexpectedly fast an additional solvation effect influences solvolysis leading to delocalized cations. 

Most recorded mass spectra show a parent ion (1 89,90 major fragmentation process, as with 2//-imidazoles, is loss of RCN, which can and frequently does occur in two different ways this often leads to the base peak. Loss of a 4-substituent to give a delocalized cation can also compete as the primary process ... 

This group is more basic than the e NH, of lysine because, on accepting H the guanidino group gives a charge-delocalized cation ... 

The counterion is quite important to the outcome of this reaction. Ion pairs, which form between alkali metal ions and the complex, induce CO lability which aids in the substitution process.1 1 Large charge-delocalized cations such as PPM are much less effective in forming ion pairs. The sulislilution process shown in Eq. 15.95 occurs readily when the counterion is Na but foils when it is PPN. Another good example of this effect can be seen by comparing NaICo CO)J and PPN [ Co[Pg.356]

Since we had shown earlier18 that the species generated upon (dark) doping were delocalized cations (polarons), one can conclude from the above experiments that in poly(thiophene) irradiation generates both cations and cation radicals in sharp contrast to what is observed in (CH)x-... 

The first example of a perfluorinated cation - F-cylopropenium - was reported by Sargeant and Krespan in 1969 [60], and it was followed by the discovery of F-benzyl [61] and F-benzoyl cations [21]. Since several unsuccessful attempts to generate F-allyl carbocations were reported [21, 40, 62], another stepwise approach to polyfluorinated delocalized cations has been developed. Stability of a polyfluorinated allylic system could be significantly increased by introduction... 

Protonation occurs on the nitrogen atom having the sp2 lone pair because both lone pairs contribute and the resulting delocalized cation is still aromatic. Pyridine is also protonated on its sp2 lone pair (it is the only one it has ) and the pyridinium ion is also obviously aromatic—it still has three conjugated 7t bonds in the ring. 

The intermediate in electrophilic aromatic substitution is a delocalized cation... 

In fact, cyclopropylmethyl compounds, cydobutyl compounds, and homoallyl compounds are all in equilibrium in acid solution and mixtures of products are often formed. The delocalized cation... 

Benzene Benzene diffuses much less rapidly than cyclohexane and the activation energy is higher ( 5 kcal/mole). Detailed studies by Lechert and co-workers(49-51) reveal that in zeolite Y, which has no delocalized cations, the benzene molecules tend to occupy tetrahedrally disposed sites with the molecules oriented parallel to the six ring at a distance 3.2l from the S2 cation. 

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