1.9 CHAPTER 1. ORGANICMOLECULES
1.9 Carboxylic Acids
Carboxylic acids are organic acids that are characterised by having a carboxyl group,
which has the formula-(C=O)-OH, or more commonly written as -COOH. In a car-
boxyl group, an oxygenatom is double-bondedto a carbon atom, whichis also bonded
to a hydroxyl group. The simplest carboxylic acid, methanoic acid, is shown in figure
1.21. The IUPAC suffixfor carboxylic acids is -anoic acid.C
O
H OH
Figure 1.21: MethanoicacidCarboxylic acids are widespread in nature. Methanoic acid (also knownas formic acid)
has the formula HCOOHand is found in insect stings. Ethanoic acid (CH 3 COOH), or
acetic acid, is the main component of vinegar. More complex organic acids also have
a variety of different functions. Benzoic acid (C 6 H 5 COOH) for example, isused as a
food preservative.FACT
A certain type of ant,
called formicine ants,
manufacture and secrete
formic acid, which is
used to defend them-
selves against other or-
ganisms that might try to
eat them.
Physical Properties ESCY
Carboxylic acids are weak acids, in other words they only dissociate partially.Why
does the carboxyl grouphave acidic properties?In the carboxyl group, the hydrogen
tends to separate itselffrom the oxygen atom. In other words, the carboxyl group
becomes a source of positively-charged hydrogen ions (H+). This is shown in figure
1.22.