QUÍMICA ORGÂNICA III – UFPI/2009:2QUÍMICA ORGÂNICA III – UFPI/2009:2

Infravermelho: Infravermelho: RevisãoRevisão

Prof. Dr. Sidney Lima

The Spectrum and Molecular EffectsThe Spectrum and Molecular Effects

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Stretching FrequenciesStretching Frequencies

Frequency decreases with increasing Frequency decreases with increasing atomic weight.atomic weight.

Frequency increases with increasing Frequency increases with increasing bond energy. bond energy. =>=>

An Infrared SpectrometerAn Infrared Spectrometer

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FT-IR SpectrometerFT-IR Spectrometer

Uses an interferometer.Uses an interferometer.Has better sensitivity.Has better sensitivity.Less energy is needed from source.Less energy is needed from source.Completes a scan in 1-2 seconds.Completes a scan in 1-2 seconds.Takes several scans and averages them.Takes several scans and averages them.Has a laser beam that keeps the Has a laser beam that keeps the

instrument accurately calibrated. instrument accurately calibrated. =>=>

An Alkane IR SpectrumAn Alkane IR Spectrum

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An Alkyne IR SpectrumAn Alkyne IR Spectrum

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An Alcohol IR SpectrumAn Alcohol IR Spectrum

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An Amine An Amine IR SpectrumIR Spectrum

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A Ketone A Ketone IR SpectrumIR Spectrum

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An Aldehyde An Aldehyde IR SpectrumIR Spectrum

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O-H Stretch of a O-H Stretch of a Carboxylic AcidCarboxylic Acid

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An Amide An Amide IR SpectrumIR Spectrum

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A Nitrile A Nitrile IR SpectrumIR Spectrum

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Summary of IR Summary of IR AbsorptionsAbsorptions

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Strengths and LimitationsStrengths and Limitations IR alone cannot determine a structure.IR alone cannot determine a structure.Some signals may be ambiguous.Some signals may be ambiguous.The functional group is usually indicated.The functional group is usually indicated.The The absenceabsence of a signal is definite proof that of a signal is definite proof that

the functional group is absent.the functional group is absent.Correspondence with a known sample’s IR Correspondence with a known sample’s IR

spectrum confirms the identity of the spectrum confirms the identity of the compound. compound. =>=>

Adapted by Organic Chemistry, 5th EditionL. G. Wade, Jr.