Analysis of IR Spectra - Altervista · Characteristic IR Absorptions 4000–3200 cm–1:...
Transcript of Analysis of IR Spectra - Altervista · Characteristic IR Absorptions 4000–3200 cm–1:...
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Analysis of IR Spectra
• identification of functional groups present (analysis of absorption bands)
• identification of unknown compounds (spectrum matching–fingerprint region)
• account for the wavenumber, intensity, and shape of the absorption bands
• usually not practical (or possible) to assign every observed band in the spectrum
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Characteristic IR Absorptions
4000–3200 cm–1: 3000–2700 cm–1:
• O–H stretch (alcohols)
• N–H stretch (amines)
• C–H stretch (alkynes)
3200–3000 cm–1:
• =C–H stretch (alkenes)
• =C–H stretch (aromatics)
• O–H stretch (–CO2H)
• C–H stretch (alkanes)
• C–H stretch (aldehyde C–H)
2700–2000 cm–1:
• CΞN stretch (nitriles)
• CΞC stretch (alkynes)
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Characteristic IR Absorptions
2000–1600 cm–1: 1300–1000 cm–1:
• C–C–O stretch (alcohols)
• C–O–C stretch (ethers)
• C=O stretch (carbonyls)
• C=C stretch (alkenes)
• N–H bend (–NH2)
1600–1200 cm–1:
• C=C stretch (aromatics)
• C–H bend (alkanes)
1000–500 cm–1:
• C–H rock (alkanes)
• =C–H bend (alkenes)
• =C–H bend (aromatics)
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functional group region
4,000–1,500 cm–1
fingerprint region
1,500–400 cm–1
• assign all bands to functional groups
• spectrum matching
• assign only intense and broad bands
–OH–CH
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The 3,000 cm–1 Line
• divides the C–H stretching bands for saturated and unsaturated hydrocarbons
saturated
below 3,000 cm–1
unsaturated
above 3,000 cm–1
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The 3,000 cm–1 Line
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IR Spectrum of Hexane
CH3 CH2 CH2 CH2 CH2 CH3–C–H stretches
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IR Spectrum of 1-Hexene
CH2 CH CH2 CH2 CH2 CH3
=C–H stretch C=C
stretch
=C–H bends –C–H stretches
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Alkene Out-of-Plane =C–H Bends
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IR Spectrum of Toluene
CH3
=C–H stretch
out-of-plane C–H bends
ring C=C stretches
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Aromatic Out-of-Plane C–H Bends
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out-of-plane C–H bends
745 cm–1
740–770 cm–1
770, 690, cm–1
760–810 cm–1
680–710 cm–1
800 cm–1
800–855 cm–1
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IR Spectrum of Toluene
CH3
overtone bands
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Aromatic Overtone Bands