The absorption band

The absorption band

1. PRESENTATION ON TYPES OF ABSORPTION BANDS 5/9/2016 1

2. PRESENTED BY: Khondaker Afrina Hoque . ID: 1114015 , Reg:900048 Sesssion: 2011-2012. Department of chemistry. Comilla University . 5/9/2016 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. 5/9/2016 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. 5/9/2016 4

5. K* bands. Transition   *. Examples : 1 ) dienes, polyenes, enones etc conjugated system containing compounds. 2) Aromatic compounds substituted by chromophores. Intensity : 10 4 . Solvent effect : ‘ e nes’ and ‘enones’ are effected differently by changing the polarity of the solvent . Enones show red shift with increasing the polarity of the solvent. 5/9/2016 5

6. TABLE1:K* BAND TRANSITION compound transition  max  max Acrolein    210 11500 Styrene    214 12000 Acetophenone    240 13000 Butadiene 1,3    217 21000 2,3- dimethyl butadiene    226 21400 5/9/2016 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) 5/9/2016 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 5/9/2016 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. 5/9/2016 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 5/9/2016 10

11. E-bands. Transition :    *. Cause : double bonds in benzenoids . Characterised by E 1 and E 2 bands. E1-lower wavelength. E2-longer wavelenth. 5/9/2016 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 5/9/2016 12

13. Summary of UV- Absorption Bands. Band Transition Example Cause/Source  (  m) log  max ---    * hexane alkanes ( sat’d HC’s) < 200 E    * C 2 H 4 , 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 E 1    * benzenes double bonds in benzenoids 180 - 190 variable E 2    * benzenes double bonds in benzenoids ~ 200 variable --- n   * CH 3 NH 2 , CH 3 OH, CCl 4 most heteroatoms in saturated cpds. 160 - 190 2.3 - 4.0 R n   * acetone, MEK heteroatoms in unsaturated cpds. > 250 1.0 -1.7 5/9/2016 13

14. THANKS TO ALL…….. 5/9/2016 14