Electromagnetic Spectrum

5.7 X X X X X Electromagnetic Spectrum (Kcal/mol)

Pi and non-bonding electrons Electromagnetic Spectrum Proton Spin Molecular Rotation Molecular Vibration and rotation nucleus valence electrons

Pi and non-bonding electrons Electromagnetic Spectrum Proton Spin Molecular Rotation Molecular Vibration and rotation nucleus NMR MicrowaveInfraredUltraviolet - Visible Mass Spectrometry X-ray diffractometry valence electrons

Infrared Spectroscopy To here!From here… Functional Groups: √ OH × C=O × C=C √ C-O Infrared (IR) Spectroscopy gives information on the functional groups within molecules

Infrared Spectroscopy

Typical stretching vibrations of a methylene group 12a–8

Different kinds of bending vibrations for a methylene group

RockingWaggingTwisting Symmetrical stretching Antisymmetrical stretching Scissoring

Schematic diagram of a typical infrared spectrophotometer

Fourier Transform Spectrometer, Interferogram and Spectrum

Factors affecting IR Stretch Frequency Masses of atoms at ends of a bond Springs connecting small weights vibrate faster than springs with large weights. H-C > C-C H-O > C-O Type of bond (force constant) Shorter, stronger springs vibrate faster than long, weak springs C ≡ C > C=C > C-C Hookes’ Law m2m2 m1m1

Fig , p. 383 A Good Guide Low EnergyHigh Energy

Infrared spectra of 1-hexyne & 1-hexene

Infrared spectra of 1-hexene & 1-hexanol

Infrared spectra of butanal and 2-butanone

A Closer Look at Carbonyl Compounds