CHMBD 449 Organic Spectral AnalysisFall 2005Chapter 2: IR SpectroscopyAnalysisGroup Frequencies

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

IR Spectroscopy

Group Frequencies and Analysissp2 and sp Nitrogen compounds CarbonylsNitriles benzonitrile

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

IR Spectroscopy

Group Frequencies and Analysissp2 and sp Nitrogen compounds Imines and Oximes acetone oxime

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

IR Spectroscopy

Group Frequencies and Analysissp2 and sp Nitrogen compounds Isocyanates and Isothiocyanates tert-butyl isocyanate

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

IR Spectroscopy

Group Frequencies and Analysissp2 and sp Nitrogen compounds Nitro o-nitrotoluene

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

IR Spectroscopy

Group Frequencies and AnalysisSulfur Thiol (Mercaptan) 1,2-ethanethiol

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.)

IR Spectroscopy

Group Frequencies and AnalysisSulfur Sulfoxide (Mercaptan) di-butyl sulfoxideBe wary of water in the spectrum of sulfoxides

IR Spectroscopy

Group Frequencies and AnalysisSulfur Sulfone di-butyl sulfone

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

IR Spectroscopy

Group Frequencies and AnalysisSulfur Sulfonamides p-toluenesulfonamide

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

IR Spectroscopy

Group Frequencies and AnalysisPhosphorusPhosphines tri-butylphosphine

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

IR Spectroscopy

Group Frequencies and AnalysisPhosphorusPhosphine Oxides, Phosphate Esters tri-butylphosphate

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

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