lecture 8 - chapter 2-9-19-05
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CHMBD 449 Organic Spectral AnalysisFall 2005Chapter 2: IR SpectroscopyAnalysisGroup Frequencies
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IR Spectroscopy
Group Frequencies and Analysissp2 and sp Nitrogen compoundsNitriles The other triple bond group observed in IR, due to the higher dipole change during the stretching vibration, this band is more intense than CCs.
Group Frequencies (cm-1):
CN2250Stretch (sym.)n sensitive to change from conjugation; usually stronger than CC
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IR Spectroscopy
Group Frequencies and Analysissp2 and sp Nitrogen compounds CarbonylsNitriles benzonitrile
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IR Spectroscopy
Group Frequencies and Analysissp2 and sp Nitrogen compoundsImines and Oximes Often referred to as derivatives of carbonyl compounds, these groups are not often encountered in routine IR obs.
Group Frequencies (cm-1):
C=N (imine and oxime)1685-1650Stretch (sym.)n sensitive to change from conjugation; usually stronger than CCO-H(oxime)3250-3150StretchH-bond effectsN-O(oxime)965-930Stretch
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IR Spectroscopy
Group Frequencies and Analysissp2 and sp Nitrogen compounds Imines and Oximes acetone oxime
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IR Spectroscopy
Group Frequencies and Analysissp2 and sp Nitrogen compoundsIsocyanates and Isothiocyanates Reactive groups, not often observed in routine qualitative IR
Group Frequencies (cm-1):
N=C=O ~2270Stretch (sym.)broad n band coupled vibrationN=C=S~2125Stretch (1 or 2 bands)broad n band coupled vibration
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IR Spectroscopy
Group Frequencies and Analysissp2 and sp Nitrogen compounds Isocyanates and Isothiocyanates tert-butyl isocyanate
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IR Spectroscopy
Group Frequencies and Analysissp2 and sp Nitrogen compoundsNitro Useful, easily incorporated group on aromatic rings, less often encountered on alkyl compounds
Group Frequencies (cm-1):
1600-15301390-1300Stretch (asymm.)Stretch (sym.)Aliphatic nitro1550-14901355-1315Stretch (asymm.)Stretch (sym.)Aromatic nitro
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IR Spectroscopy
Group Frequencies and Analysissp2 and sp Nitrogen compounds Nitro o-nitrotoluene
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IR Spectroscopy
Group Frequencies and AnalysisSulfurThiols and Sulfides Sulfur, due to its large size shifts most observed IR bands to lower frequencies often out of the observed region
Group Frequencies (cm-1):
S-H(thiol)2550Stretch (sym.)Unique region of IR spectrumC-S-CNo useful information
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IR Spectroscopy
Group Frequencies and AnalysisSulfur Thiol (Mercaptan) 1,2-ethanethiol
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IR Spectroscopy
Group Frequencies and AnalysisSulfurSulfoxides and Sulfones Oxidized sulfur, the SO bonds are useful for determining oxidation state, if the presence of sulfur is known
Group Frequencies (cm-1):
SO1050Stretch (sym.)OSO~1375~1150Stretch (asymm.)Stretch (sym.)
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IR Spectroscopy
Group Frequencies and AnalysisSulfur Sulfoxide (Mercaptan) di-butyl sulfoxideBe wary of water in the spectrum of sulfoxides
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IR Spectroscopy
Group Frequencies and AnalysisSulfur Sulfone di-butyl sulfone
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IR Spectroscopy
Group Frequencies and AnalysisSulfurSulfonic Acids, Sulfonamides and Sulfonates Sulfur equivalent of the carboxylic acid derivatives; the O or N groups act as we have observed
Group Frequencies (cm-1):
OSO~1375~1150Stretch (asymm.)Stretch (sym.)As for sulfones groups bound to sulfur identify the group, just as with the carboxylic acid derivatives differ from ketonesS-O(acid & sulfonate)1000-650StretchMay appear as several bandsO-H & N-HAs for the carboxylic acid derivatives
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IR Spectroscopy
Group Frequencies and AnalysisSulfur Sulfonamides p-toluenesulfonamide
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IR Spectroscopy
Group Frequencies and AnalysisPhosphorusPhosphines Phosphorus in its lowest oxidation state many bands that overlap with other useful regions; exercise caution in interpretation using IR
Group Frequencies (cm-1):
P-H2320-2270990-885Stretch (sym.)BendPH21090-1075840-810Bend, two bandsP-CH31450-13951350-1255Bend, two bandsP-CH2-1440-1400Bend
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IR Spectroscopy
Group Frequencies and AnalysisPhosphorusPhosphines tri-butylphosphine
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IR Spectroscopy
Group Frequencies and AnalysisPhosphorusPhosphine Oxides More common to observe these phosphorus compounds
Group Frequencies (cm-1):
Phosphate Esters, Acids and Amides Often encountered in biological systems
Group Frequencies (cm-1):
PO1210-1140Stretch (sym.)
PO1300-1240Stretch (sym.)R-O1088-920Stretch, 1 or 2 bandP-O845-725Stretch
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IR Spectroscopy
Group Frequencies and AnalysisPhosphorusPhosphine Oxides, Phosphate Esters tri-butylphosphate
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IR Spectroscopy
Group Frequencies and AnalysisHalogensFluorides and Chlorides Smaller halogen bonds to carbon in observed frequency range
Group Frequencies (cm-1):
Bromides and Iodides Not often obs. Due to low n of C-X stretch
Group Frequencies (cm-1):
C-F1400-1000Stretch (sym.)Monofluoroalkyl at lower nPolyfluoroalkyl at upper nAryl fluorides up to 1450C-Cl785-540StretchDifferent conformers may give split peaks
C-Br650-510StretchBend is obs. at ~1200C-I600-485StretchBend is obs. at ~1150
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IR Spectroscopy
End of IR Notes!!!
All Lecture notes will be consolidated into two sections theory and group frequency
Tentative Schedule:Workshop on Wednesday and Friday bring problems, or I will bring some more unknowns to work on you may bring quiet lunch
Exam is next Monday, the 26th tentatively scheduled for 5 PM in Hammermill 40 consumables will be provided
No class that day, but I will come here (Science 123) with all notes, etc. if you want more help before the exam
Office hours, Friday Noon 3 PM
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