Structural Determination (IR)

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Structural Determination (IR). Lab 9. Electromagnetic Spectrum :. Electromagnetic Spectrum :. Frequency (v): the number of complete wave cycles in a second. Given in hertz(Hz) Wavelength(λ): distance between any two peaks or troughs of the wave. C: speed of light ( 3x10 m/sec ) - PowerPoint PPT Presentation

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Structural Determination (IR)

Lab 11Structural Determination(IR)Electromagnetic Spectrum :

Frequency (v): the number of complete wave cycles in a second.Given in hertz(Hz)Wavelength(): distance between any two peaks or troughs of the wave.C: speed of light (3x10 m/sec)

Energy of the waves: It is proportional to its frequency and inversely proportional to its wavelength.Electromagnetic Spectrum :8

E = ____hc

Electromagnetic Spectrum :energyInfrared Region (IR)IR photons do not have enough energy to cause electronic transition, but they can cause groups of atoms to vibrate with respect to the bonds that connect them.Each trough is caused because energy is being absorbed from that particular frequency of infra-red radiation to excite bonds in the molecule to a higher state of vibration.Molecular vibration:the covalent bond between two atoms acts like a spring.1-StretchingThe bond will stretched or compressed.

Symmetrical stretchingAsymmetrical stretchingInfrared Region (IR)2-Bending:In- plane bending (scissoring and rocking )Out of plane bending (wagging and twisting)

scissoringrockingwaggingtwisting

Infrared Region (IR)Infrared Spectra:4000-2500 cm-1 single bonds N-H, C-H, O-HN-H 3300-3500 broad with spikesO-H 3000-3600 broadC-H 2800-3300

2500-2000 cm-1 triple bonds CC ,C NCC 2100-2200 moderate or weak

2000-1500 cm-1 double bond C=C ,C=OC=O 1750C=C 1640-1680Below 1500 cm-1 fingerprint regionFingerprint region: (from 1500-500 cm)Contains very complicated series of absorptions, mainly due to all manner of bending vibrations.

Infrared Spectra:

C-H stretching (2800 3300) cm -1Alkenes : C=C (1640 1680) cm -1Alkynes : CC (2100 2200) cm -1Infrared Spectra:Infrared Spectra:

O-H alcohol:3000 - 3600 cm- broad peakInfrared Spectra:

Carbonyl compounds:C=O 1700 cm-1Ketones, aldehydes, carboxylic acidsInfrared Spectra:

Amines:N-H: 3300-3500 cm- broad with spikes.N-H2: 3300-3500 cm- fork like.Infrared Spectra:

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