Chemistry Reference
In-Depth Information
the specific heteroatoms, electronegativity of the heteroatoms is the driving force
influencing polarity. Thus, the more electronegative the atom, the greater the affinity
of electrons for this atom. As a calibration for electronegativity, the periodic table of
the elements serves as an excellent resource. Specifically, moving from left to right
and from bottom to top, electronegativity increases. For example, nitrogen is more
electronegative than carbon, and oxygen is more electronegative than nitrogen.
Likewise, fluorine is more electronegative than chlorine, and chlorine is more electro-
negative than bromine. It is important to note that the influence of electronegativity
on polarity is so strong that simply replacing a carbon atom with a heteroatom is
enough to impart strong changes in polarity compared to the parent structure.
Figure 1.3 illustrates common organic functional groups as components of common
organic molecules.
Polarity in organic molecules is generally represented as partial positive (
d
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)
charges and partial negative (
d
2
) charges.Thesepartial charges are induced
based upon the presence of heteroatoms either by themselves or in groups. These het-
eroatoms, as described in the previous paragraph and in Figure 1.3, define the various
functional groups. Returning to the example of ethane as a nonpolar parent, Figure 1.4
illustrates how polarity changes are influenced by the introduction of heteroatoms and
functional groups. As shown, heteroatoms such as nitrogen, oxygen, and halogens,
due to their increased electronegativities compared to carbon, adopt partial negative
charges. This causes adjacent carbon atoms to take on partial positive characteristics.
Figure 1.4 How functional groups influence polarity.
