The answer is that a carbon atom is well-shielded from any attacking
group by the four atoms tetrahedrally placed around it. There are
no "open sides" exposed to attack (see movie, right).
In addition, carbon and hydrogen are of approximately equal electronegativity.
The C-H bond is nonpolar, so there is no excess or deficiency of
charge on either type of atom.
Most organic reactions take place by electrophilic or nucleophilic
attack (see boxes on next page). A slight positive charge on an
atom encourages attack by a nucleophile (e.g., OH-,
and a slight negative charge invites electrophilic attack (e.g.
In hydrocarbons, carbon has neither charge, hence it is little
affected by these attacking groups.
This property, plus the tetrahedral shielding around the carbon
atom, means thatalthough saturated hydrocarbons may be thermodynamically
able to react, they have no convenient mechanism for doing so, and
will react only slowly.