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Molecular Spectroscopy

Molecular Spectroscopy. Molecular spectroscopy The study of which frequencies of electromagnetic radiation are absorbed or emitted by a particular substance and the correlation of these frequencies with details of molecular structure. we study three types of molecular spectroscopy.

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Molecular Spectroscopy

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  1. Molecular Spectroscopy • Molecular spectroscopyThe study of which frequencies of electromagnetic radiation are absorbed or emitted by a particular substance and the correlation of these frequencies with details of molecular structure. • we study three types of molecular spectroscopy

  2. Molecular vibrations • Fundamental stretching and bending vibrations for a methylene group.

  3. Molecular Vibrations • For a molecule to absorb IR radiation • the bond undergoing vibration must be polar and its vibration must cause a periodic change in the bond dipole moment. • Covalent bonds which do not meet these criteria are said to be IR inactive. • The C-C double and triple bonds of symmetrically substituted alkenes and alkynes, for example, are IR inactive because they are not polar bonds.

  4. Infrared Spectroscopy • Infrared spectrum of 3-methyl-2-butanone. Fingerprint Region: Highly Complex and Unique for Every Molecule C-H Stretching

  5. Correlation Tables • Infrared stretching frequencies of selected functional groups. More Valuable Less Valuable Potentially difficult to distinguish between one-another, but good indication of heteroatom-hydrogen bond Almost all organic molecules have C-H bonds C=C often too weak or encroaching on fingerprint region Signature Stretch. Very strong, very identifiable Buried in fingerprint region

  6. Carboxylic acids • Infrared spectrum of pentanoic acid.

  7. Amines • Infrared spectrum of 1-butanamine, a 1° amine.

  8. Hydrocarbons-Table 12.5 Difficult to distinguish between one-another

  9. Aromatics • Infrared spectrum of toluene.

  10. Hydrocarbons-Table 12.5 Can be useful. In fairly distinct regions

  11. Alkynes • Infrared spectrum of 1-octyne.

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