IR_Sol - INFRARED SPECTROSCOPY 1 THE ELECTROMAGNETIC...

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INFRARED SPECTROSCOPY 1
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low high Frequency ( ν ) Energy X-RAY ULTRAVIOLET INFRARED MICRO- WAVE RADIO FREQUENCY Ultraviolet Visible Vibrational infrared Nuclear magnetic resonance 200 nm 400 nm 800 nm 2.5 μ m 15 μ m 1 m 5 m short long Wavelength ( λ ) high low THE ELECTROMAGNETIC SPECTRUM THE ELECTROMAGNETIC SPECTRUM BLUE RED 2
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Infrared Spectroscopy: An Instrumental Method for Detecting Functional Groups IR spectroscopy depends on the interaction of molecules with electromagnetic radiation. IR radiation causes atoms and groups in organic molecules to vibrate with increased amplitude about the covalent bonds. The vibrations are quantized and absorb energy in particular regions of the IR portion of the em spectrum. 3
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4 1. Infrared Spectroscopy
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( ) ν = wavenumbers (cm -1 ) ν = 1 λ (cm) λ = wavelength (cm) THE UNIT USED ON AN IR SPECTRUM IS THE UNIT USED ON AN IR SPECTRUM IS ν = frequency = ν c o c = speed of light WAVENUMBERS ( WAVENUMBERS ( ν ν ) ) c = 3 x 10 10 cm/sec wavenumbers are directly proportional to frequency = ν = or c λ 1 cm/sec cm = sec 1 λ c 5
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6 The position of an absorption band (peak) in an IR spectrum is specified in units of wavenumbers ( ) ν ν = 1 λ E = h ν E ν ν = E = c λ hc λ ( λ = wavelength in cm) (E = energy) ( ν = frequency of radiation)
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Two major types : STRETCHING BENDING C C C C C Molecular vibrations: Molecular vibrations: both of these types are “infrared active” ( excited by infrared radiation ) 7
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Molecules vibrate in variety of ways Three atoms can also undergo a variety of stretching and bending vibrations. 8
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Molecules vibrate in variety of ways Two atoms joined by a covalent bond can undergo stretching vibrations where the atoms move back and forth as if joined by a spring. 9
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HOOKE’S LAW HOOKE’S LAW x 0 x 1 x K -F = K( x) m 1 m 2 K Molecule as a Hooke’s Law device restoring force = stretch compress force constant 10
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= 1 2 π c ν K μ μ = m 1 m 2 m 1 + m 2 ν = frequency in cm -1 c = velocity of light K = force constant in dynes/cm m = atomic masses SIMPLE HARMONIC OSCILLATOR
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This note was uploaded on 03/07/2011 for the course CHEM 302A taught by Professor Chellappahchanmugathas during the Winter '11 term at California State University Los Angeles .

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IR_Sol - INFRARED SPECTROSCOPY 1 THE ELECTROMAGNETIC...

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