organic compounds contain other atoms besides carbon that
contribute significantly to the physical and
chemical properties of the compound. These atoms are called heteroatoms, and the groups they form, functional groups. The presence of heteroatoms radically changes
physical and chemical properties of the compounds to
which they are bonded. In fact, the
carbon— heteroatom bonds and the carbon—carbon multiple
bonds are the main sites where chemical reactions
Organic compounds are arranged into
classes according to the particular functional groups that
they contain. Members of each class of compounds share
common chemical and physical characteristics. The names of
organic compounds are assigned according to the class of
the compound as determined by the functional groups.
1. Drawing Organic Structures
are actual, three-dimensional entities.
Their structure is a major factor that determines their
physical properties and the way one molecule interacts
with another molecule. Because molecules are normally too
small to see, chemists have devised ways to visually
represent molecules. One way is by using a two- dimensional structural formula like that of the hydrocarbon heptane.
A two-dimensional structural formula of a hydrocarbon shows all of the atoms with all of their bonds in the plane of the page.
Hydrocarbons are compounds composed only of carbon and hydrogen atoms.
A condensed structural formula includes all of the atoms but uses line bonds to emphasize the main structural characteristics of the molecule.
the backbone of all organic compounds. Each carbon
atom in a hydrocarbon forms a total of four bonds.These
bonds are combinations of single bonds with hydrogen
atoms and single or multiple bonds with other carbon atoms.
For molecules that contain a large number of atoms or
complex structures, drawing every bond and every atom
is time and space consuming. A common notation developed
to abbreviate the drawing without sacrificing the
clarity of the structure is the condensed structural formula shown below for heptane:
Taking out the lines representing the carbon—carbon bonds condenses this formula still more:
Heptane has five repeating —CH2—
groups, called methylene groups. Because many organic
molecules have such repetitive groups, an even more
condensed notation shows these repeating units. Using this
notation, the formula for heptane is as follows:
The bond-line structural formula
is the notation that most organic chemists prefer to use. Bond-line
formulas are easy to draw and quickly convey the essential structure of a
molecule. Both the ends and the angles of the structure represent the
carbon atoms. C—H bonds are not shown, but you should assume that the
appropriate number of hydrogen atoms is present to complete the four
bonds required by carbon to have its octet of electrons. The bond-line
formula for heptane looks like this:
formulas represent the carbon atoms as the intersection of lines and as
line ends. You assume all the hydrogens needed to complete carbon’s
hydrocarbons are straight chains; many are rings.
Chemists use the same structural formulas for them.
Because the illustration of the two-dimensional
structural formula of methylcyclopentane is so cluttered, it
does not clearly show the ring.
The condensed structural formula is clearer.
The bond-line structural formula is even clearer. Thus, chemists use it most frequently.
chemists combine the bond-line and condensed notations to clarify a
structure or emphasize specific features. This formula also represents