Type c Systems

DHIs 31-33 containing podand crown ether groups were obtained by routes (a) or (b).35,36 DHI molecules of types 34—36 possessing long alkyl chains were 

The UV spectra of spiro[l,8a]dihydroindolizine 7 show two typical maxima, one at 240-250 and the other at 360-410 nm. The colored form (betaine) 9, absorbs in the range of 500-700 nm. Similar absorption ranges are observed for the 

The different absorption bands in DHI 7 can be assigned to the following excitations The band at 360-410 nm results from a locally excited k-k transition. 

According to a modified intermediate neglect of differential overlap (MINDO)/3 calculation, the highest occupied molecular orbital (HOMO) of a dicyanoDHI 7 shows a wave function similar to the lowest unoccupied molecular orbital (LUMO). Thus a locally excited (LE) transition (n-Jt ) is most probably hidden under this band. The assignment of a second band of 7 is less clear. 

If the colored form has a relatively fast fading rate, the maxima of the extinction coefficient cannot be recorded correctly. The procedures described in Ref. 3 can be employed in this case. 

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Most of the known heteropentalene mesomeric betaines are of type A and type B but interest has recently begun to focus on type C systems. At present only a single example... 

Too little is known about the chemistry of type C heteropentalene mesomeric betaines to justify a discussion of their general features. In their chemical reactions, type C systems are expected to show a mixture of type A and type B character (77T3203) and the limited information which is available supports this view. 

With N-phenylmaleimide, the derivative (125) reacts as a thiocarbonyl ylide giving the cycloadduct (126 65%). When DMAD is used as 1,3-dipolarophile, the 2 1 adduct (127 82%) is formed. This type C system, therefore, is clearly exhibiting both type A and type B character (76JOC129). 

Type C systems exhibit both a LCST and an UCST. This closed-loop phase behavior occurs in some highly polar systems (Siow et al., 1972). Type D systems exhibit neither a LCST nor a UCST. This is either because the LCST is below the freezing point of the mixture. 

Shifts also appear in H2 consumption for Type C systems prepared by coimpregnation with Ni and A1 salts. In these cases, there is a second H2 consumption peak beyond 900 K. This may be explained by the reduction of stable mixed oxides of the Ni aluminate type (ref. 6). 

Figure 12.5 shows the characteristic signal temperature plots obtained with these systems. It can be seen that a plateau is reached for types (a) and (b). At this point the output of the device is independent of temperature, indicating that the reaction is diffusion-controlled at a point remote from the sensor, that is, the sinter in type (a) and the chimney entry in type (b). No such plateau exists for the type (c) system. Operation of the detector under diffusion-controlled conditions limits the response time to several seconds, but offers several advantages ... 

Figure 8.28 Photomicrographs of three types of W/O/W multiple-emulsion droplet, identified by Florence and Whitehill [150]. (a) Type A (b) type B and (c) type C systems obtained using isopropyl myristate as the oil phase with different surfactant mixtures.

In Type C systems it is possible to allow the processes to run asynchronously. This is acceptable if the processes are well partitioned. Cost and compactness may be reasons for running independent processes in such an environment but from the safety point of view, if the processes are independent then running a system which introduces the possibility of interaction means that extra testing must be undert en to demonstrate that no interaction takes places where none was intended. One way of reducing this testing overhead is to decompose the PES, allocating specific system functions to... 

This type of system should be more traceable than type B or type C systems because the processes request input and wait for its arrival before continuing execution. Therefore we can observe the data areas at any time later sure in the knowledge that what we see now is the same data as the process logic used at some point earlier. Type B and type C systems allow data to be updated after processing possibly leading to confusion in interpreting results. 

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