This presentation summarizes the main types of absorption bands found in spectroscopy: K*, R*, B-, and E-bands. Each band corresponds to a different electronic transition. The K* band corresponds to a π → π* transition in conjugated systems. The R* band is a n → π* transition in unsaturated compounds containing heteroatoms. The B-band is a π → π* transition in aromatic compounds. Finally, the E-bands are π → π* transitions characterized by two bands, E1 at lower wavelength and E2 at higher wavelength, found in benzenoid compounds. Examples are provided of characteristic wavelengths and intensities for each type of transition.

1. PRESENTATION ON
TYPES OF ABSORPTION BANDS
11/16/2017 1

2. PRESENTED BY:
Khondaker Afrina Hoque .
ID: 1114015 , Reg:900048
Sesssion: 2011-2012.
Department of chemistry.
Comilla University.
11/16/2017 2

3. THE ABSORPTION BAND
An absorption band is a range of wavelength ,
frequencies , or energies in the electromagnetic
spectrum which are characteristic of a particular
transition from initial to final state in a substance.
11/16/2017
3

4. TYPES OF ABSORPTION BANDS.
Following types of bands originates as a result of the
possible transition in a compound.
•K* Bands.
•R* Bands.
•B- Bands.
•E- Bands.
11/16/2017 4

5. K* BANDS.
Transition   *.
Examples:
1) dienes, polyenes, enones etc conjugated system containing
compounds.
2) Aromatic compounds substituted by chromophores.
Intensity: 104 .
Solvent effect:
‘enes’ and ‘enones’ are effected differently by changing the
polarity of the solvent.
Enones show red shift with increasing the polarity of the
solvent.
11/16/2017
5

6. TABLE1:K* BAND TRANSITION
compound transition max max
Acrolein    210 11500
Styrene    214 12000
Acetophenon
e
   240 13000
Butadiene
1,3
   217 21000
2,3- dimethyl
butadiene
   226 21400
11/16/201
7
6

7. R* BANDS
Transition: n  *.
Cause: unsaturated compounds containing
heteroatoms.
Intensity: less ( below 100).
•Also called forbidden bands.
Solvent effect:
with increase in polarity of the solvent shifts to
shorter wavelength.( blue shift)
11/16/2017
7

8. TABLE 2:R-BAND TRANSITION
Compound Transition max max
Acetone n  * 270 15
Acetaldehyde n  * 293 12
Acrolein n  * 315 14
Acetophenone n  * 319 50
11/16/201
7
8

9. B-BAND.
Transition:   *.
Cause: double bond containing aromatic or hetero-
aromatic molecules.
Intensity: more than R-band.
Solvent effect: hyperchromic shift in heterocyclic
aromatic compounds.
Examples: benzene, styrene phenol etc.
11/16/201
7
9

10. TABLE 3:B-BAND TRANSITION
compound transition max max
Benzene   * 255 215
Styrene   * 282 450
Toluene   * 262 174
Phenol   * 270 1450
Acetophenone   * 278 1110
11/16/2017 10

11. E-BANDS.
Transition:   *.
Cause: double bonds in benzenoids.
Characterised by E1 and E2 bands.
• E1-lower wavelength.
• E2-longer wavelenth.
11/16/201
7
11

12. TABLE 4: E-BAND TRANSITION.
max
(mm)
max max
(mm)
max
Benzene 184 50000 204 7900
Napthalene 221 133000 286 9300
Anthracene 256 180000 375 9000
Pyrrole 234 10800 288 760
Thiophene 270 6300 294 600
compounds E1-band E2-band
11/16/201
7
12

13. Summary of UV- Absorption Bands.
Band Transition Example Cause/Source  (m) log max
---   * hexane alkanes (sat’d HC’s) < 200
E   * C2H4, 1,4-
pentadiene
unconjugated, unsaturated
cpds.
<200 variable
K   * 1,3-pentadiene conjugated systems 210 -250 3.7 - 4.7
B   * benzenes double bonds in benzenoids 230 -280 2.3 - 3.3
E1   * benzenes double bonds in benzenoids 180 -
190
variable
E2   * benzenes double bonds in benzenoids ~ 200 variable
--- n  * CH3NH2, CH3OH,
CCl4
most heteroatoms in
saturated cpds.
160 -
190
2.3 - 4.0
R n  * acetone, MEK heteroatoms in unsaturated
cpds.
> 250 1.0 -1.7
11/16/201
7
13

14. THANKS TO ALL……..
11/16/2017
14