Skip to main content

Bathochromic and Hypsochromic Shift

 Bathochromic shift - It is the shift of the absorption maxima (λmax) of a substance towards longer wavelengths. It is also known as red shift. 

Since, Energy (E) is inversely proportional to Wavelength. So, in Bathochromic shift----energy decreases and wavelength increases.



In Bathochromic shift, energy decreases and wavelength increases.

Factors causing Bathochromic shift: The bathochromic shift is caused by following:

A. Extending Conjugation

i. either by increasing double bonds

ii. or by adding electron donating groups (like -OH, -NH2) in conjugation to double bonds.

B. Solvent Effects

i. The less polar (non-polar) solvents cause bathochromic shift for n-π* transitions.

ii. The more polar (polar) solvents cause bathochromic shift for π-π* transitions.

Example:

Benzene shows  π-π* electronic transitions at 255 nm. Adding auxochrome NH2 to the benzene ring makes it aniline and shifts the absorptions to 280 nm.

  

Hypsochromic shift: It is the shift of the absorption maxima (λmax) of a substance towards shorter wavelengths. It is also known as blue shift. 



In Hypsochromic shift, energy increases and wavelength decreases.

Factors causing Hypsochromic shift: The Hypsochromic shift is caused by following:

A. Removing Conjugation

i. either by decreasing double bonds

ii. or by adding electron withdrawing groups (like -CHO, -NO2) in conjugation to double bonds.

B. Solvent Effects

i. The less polar (non-polar) solvents cause Hypsochromic shift for π-π* transitions.

ii. The more polar (polar) solvents cause Hypsochromic shift for n-π* transitions.

Example:


Aniline shows  π-π* electronic transitions at 280 nm. Adding proton to NH2 group of aniline makes it anilium ion and lowers conjugation thereby shifting the absorptions to 203 nm.


The hypsochromic shift (Blue shift) and bathochromic shift (red shift) are opposite to each other.









Labels:

Comments

Post a Comment

Popular posts from this blog

Atomic Absorption Spectrometry

  Atomic Absorption Spectrometry is an absorption spectroscopic technique in which radiation of a particular frequency from a source is absorbed by non-excited neutral gaseous atoms  generated in an atomizer in their ground state. The light is absorbed in the UV-visible region and makes transitions to higher electronic energy levels. The amount  of light absorbed is quantified and this amount of absorption helps in determining the analyte concentration. (It follows Beer's Law) The concentration is measured by drawing a calibration curve  after calibrating instrument with a  standard of known concentration. Factors affecting  the amount of light absorbed Length of path transversed Concentration of absorbing atoms in the vapour state. The diagrammatic representation of Atomic Absorption Spectrometer are shown in the below diagram:  Components Used in Atomic Absorbance Spectrometer: 1. Hollow Cathode Lamp: Acts as source of radiation  It is a sha...
Post a Comment
Read more

Updated list of questions after deletion of some topics for organic spectroscopy -II

  Q 1: Explain the effect of conjugation, hydrogen bonding and steric factor on vibrational frequency? Q 2: Application of Far, Near and Mid-IR spectroscopy? Q 3: Application of NMR Spetcroscopy? Q 4: Applications of Mass Spectrometry or its advantages over other spectroscopic techniques? Q 5: Why Carbon NMR is less sensitive than proton NMR or disadvantages of Carbon NMR over proton NMR Q 6: Advantages of FT-NMR over CW-NMR or difference between FT-NMR and CW -NMR Q 7: Short Notes on Following: a.  McLafferty rearrangement b.  Magnetic Anisotropy (for alkenes, alkynes, aromatic compounds and aldehydes with diagrams) c.  Mechanism of spin-spin interaction or splitting of signals d.  Coupling constant and factors affecting it e.  Long range coupling f.  Simplification of complex spectra (High Field strength, Double irradiation or spin-spin decoupling, Use of Shift Reagents) g.  Nitrogen rule. h.  EI (Electron Impact Ionization) i.  CI (Ch...
Post a Comment
Read more

Gross and Specific Selection rules for different molecular spectroscopies

Gross selection rule   tells whether a molecule will be active or inactive in a particular Spectroscopy.   Specific selection rule tells about the allowed changes in the magnitude of energy when it is active in a particular Spectroscopy.     Rotational or Microwave Spectroscopy Gross selection rule: permanent dipole moment  Specific selection rule: ∆J = +1 or -1 ( for rigid rotor) 2. Vibrational or IR Spectroscopy Gross selection rule: change in dipole moment during vibrations Specific selection rule: ∆v = +1 or -1 ( for harmonic oscillator) 3. Raman Spectroscopy Gross selection rule: change in polarizability  Specific selection rule:   ∆J = 0, +2 or -2   ∆v = +1 or -1  4. Electronic or UV-Visible Spectroscopy Gross selection rule: No stringent rule Specific selection rule: ∆s = 0  and ∆l = +1 or -1 5. Nuclear Magnetic  Resonance or Radio waves Spectroscopy Gross selection rule: nuclear spin should be no zero  Specific se...
Post a Comment
Read more