Lonepair electrons

Hydrophilic Groups. Water solubiUty can be achieved through hydrophilic units in the backbone of a polymer, such as O and N atoms that supply lonepair electrons for hydrogen bonding to water. SolubiUty in water is also achieved with hydrophilic side groups (eg, OH, NH2, CO2, SO3 ). 

Pyrrole is possibly one of the most reactive heterocycles thanks to its lonepair electrons at the nitrogen atom. The enormous reactivity of pyrrole in electrophilic substitution reactions explains the occurrence of more than 100 naturally occurring halogenated pyrroles. Indeed, the pyrrole ring is widely distributed in nature. It occurs in both terrestrial and marine plants and animals. An illustration of the abundant complex natural pyrroles is konbu acidin A, a sponge metabolite that inhibits cyclin-dependent kinase 4 (CDK4). 

This can be rationalized by assuming that the breaking of one S—S single bond (ca. 61 kcal/Mol 6)) is nearly compensated for by the electron-rich three center bond. In other words, the linear arrangement of three centers as in /a favours an electron-rich three-center bond. The energy difference between an S—S sulfur atom on one side and an electron-rich three-center bond on the other is small. 

Normal paired lonepair R N — These two electrons may be paired or unpaired... 

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