UV-visible absorption bonds may be designed by the type of the of electronic transition from which they originate, e.g.., σ →σ* band , Π→Π* band, etc. or by letter designation. The following letter designation was proposed because more than one band may arise due to the same type of electronic transition.
1) K-bands (German:Konjugierte= conjugated): These bands originated from Π→Π* transition in compounds having a Π-Π conjugated system. The intensity of K-band is usually 104.K-band is exihibited by conjugated enes and enones. Some K bonds attributed to Π→Π* transition are given in table 1.1
2) R-Bands (German: Radikalartig =Radial-like): These band originatnated from n→Π* transition of a single chromophoric group, e.g., carbonyl or nitro group .These band are also called forbidden bands. R bands are less intense with εmax value below 100. Some R bands attributed to n→Π* transition are given in the table 1.2.
3) B-bands (Benzenoid bands): Such type of bands are appear in the benzenoid compounds so such type of bands is known as benzenoid bands.
These bands originated from Π→Π* transition in aromatic compounds.The intensity of benzenoid bands is 200nm and Λmax is 256nm are given in the table 1.3.
4) E-bands (Ethylenic Bands): Such type of bands is originated due to ethylenic bands this bands will occurs while Π→Π* transition.
Further E-bands characterized as E1 and E2. E1 and E2 E- bands are appear 18onm to 200nm.Some E1 and E2 bands due to Π→Π* transition are given in table 1.4.
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