Functional Classes I, Structure and Naming - Organic Chemistry Concepts: An EFL Approach - page 17

of ways to do this. The choice of method depends on the specific structural
feature(s) of interest.

For the beginner, the full Lewis-type structure (extended) is the safest choice.
Because every bond and atom is shown, we can avoid mistakes with the tetrava-
lent nature of carbon. After practice with examples that have different structural
features and functional groups, it becomes easier to use the shorter forms, such
as condensed and bond line types.

The condensed forms use groups of atoms and show almost no detail of
individual bonds. These groups can show all atoms, for example CH 3 - and
-CH 2 -. Alternatively, accepted short forms can be used, for example Me- for
CH 3 - and Et- for CH 3 CH 2 -. Often it is useful to use a combination of struc-
tural diagram forms. In these diagrams, only important features are shown
in full detail.

You must take care to draw any bonds between the actual bonded atoms. This
will avoid any mistakes with the valency (oxidation state) of the atoms involved.
Note that only the bond line method shows the shape of the carbon framework.
This is because every bend in the diagram represents a bonded group, for exam-
ple -CH 2 -. The ends of lines represent CH 3 - groups.
It is also useful to be able to describe the degree of substitution at saturated sp 3
carbon centers. This is simply done by counting the number of hydrogen atoms
bonded to the particular carbon. As Figure 2.2 shows, this gives rise to four types:

primary, with 3 H s on carbon;

n

secondary, with 2 H s on carbon;

n

tertiary, with 1 H on carbon; n

quaternary, with no H s on carbon. n

FIGURE 2.2
Classification of carbon centers.

It is also common to use the symbol -R to show general alkyl groups . A selection
of these are detailed in Section 2.2.3 and are derived from alkanes by removing
a hydrogen ligand.

In addition, as Figure 2.3 shows, there are different ways to show the three-
dimensional (3-D) shape of tetrahedral sp 3 centers. A tetrahedral center has four
substituents , or attached groups. The most common is to show two adjacent