Density within ring

Neutral hexakis(methylsulfonyl)benzene (see Scheme 6.23) adopts a chair conformation. On the contrary, the tube conformer appears to be inherent in the corresponding anion-radical. The methylsulfonyl fragments at positions 1 and 4 of the bent benzene ring are nonequivalent. Moreover, one methylsulfonyl moiety is nonequivalent to all of the other five (Fabre et al. 2002). Scheme 6.23 depicts an intuitively constructed picture. Localization of spin-charge density within one methylsulfonyl group causes the attraction of the other from position 4. This makes the tube conformation the most stable in the case of hexakis(methylsulfonyl)benzene anion-radical. 

The ease of this thermal 67T-electrocyclization depends on the electron density within the aromatic ring. With weak electron donors, temperatures... 

Depending on the insertion of substituents with donor or acceptor characteristics, the electron density within the phenyl ring strongly changed (A max up to 0.162). 

By contrast, the insertion of substituents with donor or acceptor characteristics changed the electron density within the heterocyclic moiety only to a minor extent (A max up to 0.017), and did not change the electron density at the 5-dimethylamino group. Thus, the term out of Equation 9 in essence describes the electronic characteristic of the phenyl ring. 

Delocalisation of the 6 n-electron system in unsaturated NHC would have consequences in the thermodynamic, structural and magnetic data and the charge density within the p orbitals of the ring atoms [11]. 

Equations 2.56 and 2.57 suggest that it is reasonable to imagine two components of the current density at every point which are distributed in an entirely different manner. In order to investigate their distribution let us first of all understand the physical meaning of the term (o-pw/47r)(rMr/Zi ) which is present in both expressions for the current density components. It is obvious that the current flow in the medium can theoretically be subdivided into currents flowing in a series of elemental toroids or within rings which have a common axis with that of the dipole and which lie in planes perpendicular to this axis as shown in Fig. 2.6. 

Tests carried out on transformer models of a ring type and with enclosed magnetic fields (by means of superconducting sheet metals) showed that with suitable layout current densities up to about 150 amp/mm in niobium wires (0,004 in. diameter) could be reached without destroying the superconductivity of the wires. Flux densities within the winding spaces measured up to 400 gauss. 

Within-ring density variations can cause problems because of the differential shrinkage at the ring boundary. Subsequently, severe drying stresses may cause deformation and internal checking (Booker, 1994). Further, alow absolute density in earlywood can result in collapse on drying, particularly under high-temperature conditions (Booker, 1996). 

T 2-ene fonn. NMR data suggested that the metal-coupling patterns reflected the variation in charge density within the substituted cyclopentadienyl ring. 

All molecules with nonbonding electron pairs (e.g., H2O, AOH, ROR, 7 NH2, / SH, RSR, etc.) are, by definition, Lewis bases with a degree of nucleophilicity. Their electrochemical oxidation potential is a measure (1) of the ease of removal for one of the electron pair of electrons and (2) of relative nucleophilicity (the less positive the potential, the more nucleophilic). Aromatic molecules with Lewis-base substituents are easier to oxidize than the aliphatic forms of the substituents (e.g., PhOMe, -1-1.75 V vs SCE MeOH, -1-2.5 V vs SCE) because the aromatic ring provides a means to delocalize the positive charge and electron spin that would result from electron removal (in the case of PhOMe, there are five additional hydrogen atoms to share the positive charge and six unsaturated carbon centers to share the spin density). Within this context, the water molecule in a nonbasic solvent matrix is the most resistant to electron removal,... 

---