Dialkylammonium cation

Structural characterisation of 58 and 59 have demonstrated that the PF, anion is located in the cleft between the two dialkylammonium cations forming hydrogen-bonds with the benzylic hydrogen atoms of one of the cations and with one of the hydrogen atoms of a hydroquinone ring. In contrast, a polymeric as-... 

Stoddart and coworkers have used imine condensation in two different contexts to form interlocked molecules. The authors have modified the crown ether component of their dialkylammonium / D B24C8 system to incorporate reversible imine subunits which allow for dynamic clipping around dialkylammonium cation 91 [60], Three diformyl spacers (92-94) have been investigated with the same acyclic diamine 95 for their thermodynamic stability and kinetics of macrocyclization (96). However, reduction with BH3 to the kinetically trapped macrocyclic secondary diamine has only been reported for reaction of the 2,6-diformylpyridine derivative (Scheme 10.19 97) [60a]. 

There are a number of examples in which dialkylammonium cations have been shown to form complexes with crowns in which the NH2 group is held in the plane... 

Regarding the threading with dialkylammonium ions, simple ethers of calixarenes can be seen as modified crown ethers and in principle they should be able to give cn io-complexation of such organic cations in a similar way [6], Unfortunately, with the notable exception of some calix[5]arene derivatives [16], simple ethers of calix[n]arenes do not complex halide, hexafluorophosphate or tetraphe-nylborate salts of dialkylammonium cations. 

Regarding the kinetic aspects of the threading process of calixarene-wheels with dialkylammonium cations, it was evidenced that the time necessary to reach the threading equilibrium are particularly sensitive to the length of the axle. Thus, while with short dipentyl/dibenzylammonium axles the threading equilibrium is reached immediately after mixing with both calix[6]arene wheels la and lb [17], with a longer axle such as 72 h at 60 °C are necessary to reach the formation eqmlibrium of 4 cla and 4 clb pseudo[2]rotaxanes (Fig. 30.3) [22]. 

Finally, it was found that the smaller 18-membered dihomooxacalix[4]arene macroring (i.e. 7a-b) cannot give the through-the-annulus threading with dialkylammonium cations because of its small dimension [24]. However, the macrocycle is able to complex such ions into its cavity, which can only be accommodated in a hook-like conformation [24]. 

Interestingly, the applicability of the weakly coordinating TFPB anion in the induction of the threading of dialkylammonium cation with macrocycles is quite general. In fact, 2 years later with respect to our first report [17], Chiu and coworkers [25] showed that by replacing the counterion of dibenzylammonium cations from hexafluorophosphate to TFPB significantly encreased the affinity of... 

Figure 5. Initial co-conformation1201 and constraints used for simulating the passage of DB24C8 over the R groups of the dialkylammonium-containing cations 8+-11+.

The influence of the membrane fluidity was investigated for several types of reaction. Proton abstraction by a hydrophobic hydroxamate (23) is facilitated in the presence of cationic micelles (Okahata et al., 1980). Dialkylammonium... 

The interaction of smectites with cationic surfactants is important for numerous practical applications of bentonites ([1] (chapter 9)). Important surfactants used in modifying bentonites are mono- and dialkylammonium chlorides ... 

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