Current density ring currents indication

The criterion of ipsocentric ring current has been used to assess aromaticity in S-N heterocycles (and related inorganic ring systems). Current density maps indicate that the ten r-electron systems [SsNs], [S4N3] " and [S4N4] ", and the fourteen r-electron system [S5N5] " support diatropic k currents, reinforced by a circulations. 

As shown in Fig. 5, although the Wiberg indices (21) of the endocyclic (P N) bonds are large (favoring an important delocalization within the ring), the electron density on the phosphorus atoms is so low that no ring current can exist, hence the delocalization remains localized within the PNP units (79). 

The rotating ring-disc electrode is perhaps the most useful extension of the idea of the rotating disc. We have already seen (cf. Eq. 32D) that the ring current has the same form as the disc current, namely that it is also proportional to the bulk concentration of the electroactive species C° and to the square root of the rotation rate. A numerical comparison of Eqs. 32D and 25D shows that the current density at the ring is higher than at the disc, indicating that some increase in analytical sensitivity may be attained. This, however, is not the... 

Fig. 39. Long-term cyclization of the cell Pb/60% H2F2/CPP. The current densities on charge (1 h) and discharge (down to 1 V) were each 3 mA/cm. Cycle numbers are indicated by ring numerals. After [157],...

Fig. 1 Schematic of a wafer plating cell depicting the current feed contact ring (right), and a numerical simulation5 of the initial current distribution (left), indicating about a 10 1 initial current density ratio between edge (344 mA/cm2) to center (33 mA/cm2) under the simulated conditions (acidified copper sulfate electrolyte).

The H-n.m.r. spectrum of azulene, with signals in the range 6 6.92-8.12, clearly indicates that it sustains a diamagnetic ring current [46]. The coupling constant.s are also in accord with this. The C-n.m.r. spectrum shows chemical shifts which correlate with the calculated electron densities for the different sites [17]. 

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