Electronegativities biologically important atoms

Interest in organofluorine chemistry is growing at a rapid pace. Fluorine as a substituent can significantly affect the properties of molecular systems. Its high electronegativity and small atomic volume have been used to probe reactivity—especially that of biologically important molecules. 

PTs between electronegative atoms are fast and reversible. They are enormously important, not only in organic and inorganic chemistry but also in biology. In terms of arrow pushing, PTs look very much like Sj 2 displacements ... 

Molecular geometry is tremendously important in understanding the physical and chemical behavior of a substance. Molecular polarity, for example, is one of the most important consequences of molecular geometry, because molecular polarity influences physical, chemical, and biological properties. Recall from Section 8.4 that a bond between two atoms of different electronegativities is polar and that a diatomic molecule containing a polar bond is a polar molecule. Whether a molecule made up of three or more atoms is polar depends not only on the polarity of the individual bonds, but also on its molecular geometry. 

Perhaps the most important noncovalent interaction in biological molecules is tbe hydrogen bond, an attractive interaction between a hydrogen bonded to an electronegative O or N atom and an unshared electron pair on another O or N atom. In essence, a hydrogen bond is a very strong dipole-dipole interaction... 

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