Organic Families and Their Functional Groups
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Such a huge number of organic compounds requires organization.
They are sorted into organic families defined by functional groups.
Functional groups are small structural units within molecules at which most of the compound's chemical reactions occur.
For example, two of the most important families are the alcohols and the carboxylic acids.
Their functional groups, the alcohol group and the carboxyl group, respectively, distinguishes them from the rest of the other types of organic compounds.
Important Families of Organic Compounds
methanol (methyl alcohol)
acetic acid (ethanoic acid)
Symbolism shown below that you may not understand will be explained later in this topic
R, R', and R'' represent hydrocarbon groups (alkyl groups)
Only C and H present
Only single bonds
Double bond(s) between two carbons
Triple bond(s) between two carbons
The type of properties associated with a compound is different depending on the family it is in.
For example, the alkanes have just C-C and C-H single bonds.
Since C and H are so alike in electronegativity, they are least able to attract ions or polar molecules, and least able to interact with them.
The significance of this will be explained later.
To save space and time, condensed structures may be used to simplify the drawing and writing of structural formulas of organic compounds.
C-H bonds are understood, and CH3 means that three hydrogen atoms are bonded to a carbon atom.
|CH3 is understood to be
|CH3CH2OH is understood to be
||CH3OCH2 is understood to be
Functional Groups and Polar Reactants
When a polar group of atoms, like the OH group or NH group are attached to a carbon, the molecule has a polar site.
It may undergo chemical reactions when it attracts polar and ionic reactants, but it will usually be near this functional group.
This is why compounds with the same functional group have similar chemical properties, or kinds of reactions.
For example, in the amine group, both methylamine and ethylamine give the same kinds of reactions.
CH3NH2 + HCl ==> CH3NH3+ + Cl-
methylamine + hydrogen chloride ==> methylammonium ion + chloride ion
CH3CH2NH2 + HCl ==> CH3CH2NH3+ + Cl-
ethylamine + hydrogen chloride ==> ethylammonium ion + chloride ion
Only the NH2 group of the amines change in the previous two reactions, and it changes the same way in both.
The Symbol R in Structural Formulas
The symbol R, stands for the word radical, and in organic chemistry, represents alkane-like groups.
It is sometimes used to simplify equations or to summarize them.
For example, to summarize the two equations in the previous sections, you may write:
RNH2 + HCl ==> RHN3 + Cl-
The R takes care of any alkane group that you may substitute in.
It takes care of all the equations, including methylamine, ethylamine, propylamine, butylamine, etc.
It gives a simpler view of how one group, not just the individual compound, changes into another and how each group affects its properties.