Arenes arenium ions

The arenium ion/(R)-(— )-2-chlorobutane adducts. A crucial question concerns the chemical identity and the relative spatial arrangement of the components of a microsolvated system, two features of paramount importance to assess the kinetic and the mechanistic role of the corresponding ion-dipole pairs in solution. In the example reported in this section, Cacace and coworkers consider the ion-molecule complexes involved in the classical Friedel-Crafts alkylation of arenes." " At 300 K and under FT-ICR conditions, the benzenium ion CeH reacts with 2-chlorobutane C4H9CI to give the CloHj5 ion with a rate constant of 5 X 10 cm molecule corresponding to a collision efficiency of 2.5% (equations (33) or (34)). ... 

The intramolecular stabilization of germyl cation 34 by a remote aryl substituent was demonstrated by the NMR chemical shifts of the coordinated aryl ring. The chemical shift pattern found for the coordinated arene ring of 34 is characteristic for arenium ions and it closely resembles that found bissilylated arenium ions 78. 

In Ref. 6, the Bronsted superacidity of HCl in liquid chloroaluminate IL ([C2Cilm]Cl/AlCl3) was studied by the protonahon of arens during which the degree of protonahon was measured by using absorption spectroscopy. The arens were stable in the liquid chloroaluminate for many hours and their protonated forms (arenium ions) were stable for 1 h or more. 

Such limitation does not detract from the mass-spectrometric approach, which has provided valuable information on the stability of the protonated arenes, and their dissociation patterns. Moreover, it seems appropriate to mention here that, as early as 1957, Field and Franklin established a correlation between the orienting influence of substituents and the appearance potential of the corresponding ionic species, and that their proposed structure of the arenium ions observed in chemical... 

The mechanism of alkylation of arenes can be best understood as a carbocationic electrophilic aromatic substitution — a review on this aspect is available. The alkylating agent and the catalyst first form an alkyl cation or related polarized complex, which then reacts with the aromatic ring via a Wheland intermediate (arenium ion Scheme 1). 

Protonation and alkylation of arenes afford cyclohexadienyl cations (arenium ions) which are also of importance in electrophilic aromatic substitution. The hepta-methylbenzenium ion (16) is a very stable species30-, but even the parent benzenium ion (17a) has been observed as have most of its alkyl, halo, and alkoxy derivatives51. The benzenium ion (17a) undergoes a rapid degenerate rearrangement which equilibrates the seven protons over six carbons. Data for the monosubstituted benzenium ions show that (17) is the most stable of the possible isomeric forms. Positive charge... 

Anti-Markovnikov addition, 220 D-Apiose, 988, 1011 Aprotic solvents, 322, 875 D-Arabinitol, 1009 D-Arabinose, 977, 1006, 1009 L-Arabinose, 976, 1001 Arachidic acid, 1018, 1025 Arachidonic acid, 1018, 1025 Aramid polymers, 809 Archaea, 58, 299 Arene oxides, 409, 948, 1064 Arenes, 54, 398-442 biological oxidation, 409, 417, 948, 1064 infrared spectra, 519 table nuclear magnetic resonance spectra carbon, 513 table proton, 495-496 Arenium ion, 444 L-Arginine, 1055, 1059... 

An example is provided by the reaction of CT3 decay ions >vith gaseous and liquid arenes (22,23), whose results are summarized in Tables VI and VII. The highly exothermic condensation step, for example. Equation 14, Aff° = — 89 kcal mol", yields excited arenium ions, whose... 

In the liquid phase, when the ions are formed from the decay of CT4 dissolved in the pure arene, collisional stabilization is very eflFective owing to the large collision frequency, as shown by the relatively low yields of fragmentation products. Isomerization to the thermodynamically most stable arenium ion... 

The substituent effects for the dehydration of arene hydrates have been studied." The kinetics of dehydration were studied with a series of substituted arene-hydrates (84) in dilute HCIO4 solutions. The results are consistent with a rate-limiting step involving formation of the arenium ion (86) from the oxonium ion intermediate (85). Rapid deprotonation then provides the dehydration product (87). The Hammett plot of second-order... 

---