The absorption band

PRESENTATION ON
TYPES OF ABSORPTION BANDS
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PRESENTED BY:
Khondaker Afrina Hoque .
ID: 1114015 , Reg:900048
Sesssion: 2011-2012.
Department of chemistry.
Comilla University.
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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.
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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.
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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.
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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
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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)
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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
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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.
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TABLE 3:B-BAND TRANSITION
compound transition max max
Benzene   * 255 215
Styrene   * 282 450
Toluene   * 262 174
Phenol   * 270 1450
Acetophenone   * 278 1110
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E-BANDS.
Transition:   *.
Cause: double bonds in benzenoids.
Characterised by E1 and E2 bands.
• E1-lower wavelength.
• E2-longer wavelenth.
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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
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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
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THANKS TO ALL……..
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