Chemistry is one of the oldest and most fascinating fields of science. It deals
with molecules, peculiar entities that are extremely small (sub-nanometer
dimension) and unbelievably numerous and diverse. Five million different
molecular types have been discovered in Nature and at least fifty million
more have been synthesized by chemists in their laboratories. Each type of
molecule has its own composition, size, shape and structure, and therefore it
is a unique ‘‘object’’. Some molecules are simple, others are extremely complex,
as is the case for most natural molecules of biological interest. Indeed,
in the past century chemistry became the science of molecules