Chromophore, a group of atoms and electrons forming part of an organic molecule that causes it to be coloured. The ability of a compound to take up hydrogen, called unsaturation, is caused by the presence of electrons that are not strongly fixed in covalent bonds between particular pairs of atoms but occupy larger regions of space that may be associated with several atoms. There is no set rule for the identification of a chromophore. The change in position as well as the intensity of the absorption depends upon a large number of factors.
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