Neutralization indicators categories

Macrocyclic receptors have also been found to complex neutral substrates,21 and complexes of both variable and exact stoichiometries have been prepared. The latter category includes acidic CH— and NH— or polar neutral molecules, such as acetonitrile, nitromethane, benzyl chloride and dimethylmalonitrile. X-Ray data indicate complex formation to be mainly a result of hydrogen bonding and dipole-dipole interactions. Section 21.3.8 contains a more detailed treatment of these complexes. 

It was recognized centuries ago that many substances could be divided into the two general categories. Acids have a sour taste (as in lemon juice), dissolve many metals, and turn litmus paper red. Bases have a bitter taste (as in soaps), feel slippery, and turn litmus paper blue. The chemical reaction between an acid and a base is called neutralization. The products of neutralization reactions are neither acids nor bases. Litmus paper is an example of an acid-base indicator, a substance that changes color when added to an acid to a base. 

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