Answer to Question #65958 in Chemistry for sharma

Question

Explain the following terms:
(i) Auxochrome
(ii) Bothochromic shift
(iii) Hypochromic shift
(iv) Hyperchromic effect

Answer 1

(i) Auxochrome is a group of atoms that alters spectroscopic properties of the
chromophore (a molecule, or a part of the molecule that has its specific profile of
light absorption). In particular, auxochrome shifts absorption spectrum and
changes the absorption coefficient of the compound. Acidic groups (-OH, -COOH,
-SO 3 H), basic groups (-NHR, -NR 2 , -NH 2 ) and halogens (-I, -Cl, -Br) can play the role
of auxochrome in the chromophore molecules.
(ii) Bathochromic shift is the change in position of spectral band to longer
wavelength (lower frequencies). It can also be called “red shift”, as the visible
part of the spectrum at longer wavelength is red. On the contrary, hypsochromic
shift occurs to shorter wavelength (“blue shift”).
(iii) Hypochromic shift makes no sense, as hypochromicity is the effect of decrease in
absorbance. Hypsochromic shift (that may be your question) was discussed in the
previous part.
(iv) Hyperchromic effect is the opposite of hypochromic effect. That is,
hyperchromicity is the increase of absorbance of a material.