Rings, electrically charged

Structural features such as electrical charge, hydroxyl groups in the side-chains and amino atoms of the amide groups reduce the lipophilicity (increase the hydrophilicity) whereas additional methyl groups sitting on amino moieties or free positions on the benzene ring increase the fipophilicity. Biliary contrast agents with a free position have > 5. 

The cyclopentad ienyl rings (and the iron atom) of ferrocene are shown to have no electric charge by the identity of the first acid constant of ferrocene dicarboxvlic acid with that of benzoic acid (R. B. Woodward, M. Rosenblurn, and M. C. Whiting. J.- C.R. 74, i458 [1952]). 

Fig. 2 Bond lengths (in A, shown outside the rings) and bond angles (shown inside the rings) of monocyclic six-membered aromatic systems with one heteroatom from groups 14-15 and periods 2-4 devoid of electrical charges...

A correlation has been established between S 2p- electron energies measured by ESC A and 19F NMR chemical shifts in some 5-(p-fluorophenyl)-l-oxa-6,6aA4-dithiapentalenes. It appears that, in these cases, the fluorine chemical shift is a convenient evaluation of the electrical charge of the heterocyclic ring to which the p- fluorophenyl substituent is attached (74T2537). 

Cyclosilicates are those compounds with three or more tetrahedra linked in closed, ring-like structures. The ratio between Si and O is 1 3. This group includes the important gem species beryl and the tourmaline group. The 11 members of the tourmaline group display an unusual property known as piezoelectricity. When pressure is applied to a crystal, an electrical charge builds up at either end of it. This makes these minerals useful in pressure gauges and other electrical equipment. Quartz and a few other, less common minerals, also display this property. 

The ring compound, benzene, C6H6, is given in a tr-bond picture only but a similar streamer picture can be drawn for it also, showing clouds of electric charge above and below the plane of the ring. 

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