ALKANOIC ACIDS

An alkanoic acid is a compound that has the general structure

The homologous series called alkanoic acids has the general formula C n H 2n O 2 w ith n > 0 or C n H 2n+1 COOH with n > 0. Models of the simplest alkanoic acids, along with the alkanes and alkanols they come from. Names of alkanoic acids

Naturally occurring organic acids ? why

Properties The carboxylic acid group has a trigonal planar arrangement of bonds around the central C atom; this means that the double bond and the two single bonds are at angles of 120° to one another. This happens because there are three sets of electrons around that C atom as was the case in the methanal molecule Because it has two electronegative O atoms on it, the carboxylic acid group is highly polar

Because of the two O atoms on the one C atom, alkanoic acids are more polar than the corresponding alkanols. It is this increased polarity that makes the carboxylic compounds acidic, whereas alcohols are not. Being acidic means that carboxylic acids can easily lose a hydrogen ion to form what is called the carboxylate anion

Like alkanols, alkanoic acids contain an O — H bond and therefore can form hydrogen bonds, both with themselves and with other compounds such as water. Carboxylic acids are weak acids and undergo the usual reactions of such acids. They dissolve in sodium hydroxide solution to form soluble sodium carboxylate salts and react with sodium carbonate to form bubbles of carbon dioxide; for example for formic and acetic acids:

MELTING AND BOILING POINTS OF ALKANOLS AND ALKANOIC ACIDS

As we have just seen, both alkanols and alkanoic acids are polar molecules that can form hydrogen bonds. Consequently there are strong intermolecular forces in alkanols and in alkanoic acids. Therefore they have much higher melting and boiling points than alkanes of similar molecular weight as shown above They also have quite high solubilities in water. To show the effect of polarity and/or hydrogen bonding on physical properties we generally compare compounds with similar molecular weights, because the dispersion forces will be roughly similar in such compounds. This is because the strength of dispersion forces increases as the number of electrons in the molecule increases, and the number of electrons generally increases as molecular weight increases, at least in compounds of similar structure.

Preparation of Carboxylic Acids 1.htm