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Velocity of light (c ) = frequency (f) x wavelength (λ) • c = f λ
• All electromagnetic waves travel at the speed of light (3.00 x 108ms-1)
• Radiation with high ↑ frequency – short ↓ wavelength • Electromagnetic radiation has a particle nature and each photon carry a quantum of energy given by h = plank constant = 6.626 x 10-34 Js c = speed of light = 3.00 x 108ms-1
f = frequency λ = wavelength
hcE Short ↓ λ, Higher ↑ frequency, Higher Energy ↑ E = hf
Electromagnetic Radiation
Picture from :http://www.azimuthproject.org/azimuth/show/Blog+-+a+quantum+of+warmth
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Electromagnetic Radiation and Spectroscopy
Radiowaves
Nuclear spin
Nuclear Magnetic Resonance Spectroscopy
• Organic structure determination • MRI and body scanning
Infrared
Molecular vibration
Infra Red Spectroscopy
UV or visible
Transition of outer most valence electrons
• Organic structure determination • Functional gp determination • Measuring bond strength • Measuring level of alcohol in breath
Electromagnetic Radiation
UV Spectroscopy Atomic Absorption Spectroscopy
• Quantification of metal ions • Detection of metal in various samples
Electromagnetic Radiation Interact with Matter (Atoms, Molecules) = Spectroscopy
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Dipole change
Vibrational motion -result in a change dipole moment – IR active
Polar molecule will absorb IR • H-CI, as bond stretches, distance between atoms increases, results in change in dipole moment
Condition for molecular vibration to absorb a photon /IR
• Vibration causing oscillation in developing a change in dipole
bet opposite charged centres • Vibration of bond in HCI will cause the dipole in bond to oscillate • Causes a change in dipole moment Oscillation of bonds - Lead to oscillation of dipole - lead to change in dipole moment
Molecular Vibration
Change in dipole moment
IR frequency = Natural frequency for bond – Resonance will happen. • HCI bond has natural vibrational frequency • IR frequency match the vibrational frequency in HCI, then IR is absorb and molecule excited to vibrational state • IR absorb by bond will result in greater vibration in amplitude
IR frequency = Natural frequency for bond – Resonance will happen
IR frequency is applied
IR absorption due to molecular Vibration
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IR radiation absorbed by molecule is converted into vibrational energy within the molecule. IR frequency match the natural vibrational frequency of molecule , then IR is absorbed and resonance happen (excited vibrational state). Absorption on Y-axis and wavenumber on the X-axis. Absorption plotted two ways. • Transmittance, % (T) and Absorbance (A) • Transmittance of 100% means IR Absorbance of 0% . • Transmittance of 0% means IR Absorbance of 100%
Tran
smit
tan
ce /
%
Ab
sorb
ance
Wavenumber, cm-1
Transmittance or Absorbance of IR Spectra
Click here to view
Wavenumber, cm-1
Transmittance is Low ↓
Absorbance is High ↑
Transmittance is 100%
Absorbance is Low
IR radiation absorbed Bonds undergo Resonance
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Infra Red Spectroscopy
• Fingerprinting region (400- 1500)cm-1 – due to vibration of entire molecule, not independent functional gp • IR active – it must have an electric dipole that changes as it vibrates • IR does not have enough energy to excite electrons, only causes molecular vibration • Wavenumber = Reciprocal of wavelength (1/λ) , Unit = cm-1
• Wavenumber = 1/ Wavelength = number of waves cycles in one centimeter • Wavenumber α frequency • Wavenumber used in IR spectroscopy • Higher Wavenumber ↑ = Lower wavelength ↓= Higher ↑ frequency = = Greater Energy ↑
Infrared wavelength from (2500 – 25000)nm → Convert to wavenumber (400– 4000)cm-1
Wavenumber between 400cm-1 – 4000cm-1 Wavelength, λ = 2500nm (convert to cm) → λ = 0.00025cm → Wavenumber = 1/λ = 1/0.00025 = 4000 cm-1
Wavelength, λ = 25000nm (convert to cm) → λ = 0.0025cm → Wavenumber = 1/λ = 1/0.0025 = 400 cm-1
Wavelength, λ low ↓ → Wavenumber, 1/λ is High ↑ Speed of light, c = fλ, f = c/λ → c x 1/λ Wavenumber, 1/λ is High ↑ → f = c x 1/λ → f is High ↑ (cause 1/λ is high) → Energy = hf High ↑
Wavenumber bet 400cm-1 – 4000cm-1 IR absorption by different functional gps
Fingerprinting region
Infrared Spectroscopy
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Operating Principle of a Double Beam Infrared Spectrometer
Double beam splitter
• Directs half radiation through sample and other half through reference
• Allow radiation passing through sample and compare it with reference • Two beams recombined at detector. • Signal from sample/reference are compared to determine if sample absorb radiation emitted from source
Reference • Solvent used to dissolve sample • Reference use to eliminate instrument fluctuation, absorption due to impurities in solvent and all interferences. • Absorption of IR is only due to solute using the reference
Monochromator • Allow radiation of a particular wavelength to pass through
Fourier transformation • Allow several wavelength through the sample at the same time and analyse the results • Using mathematical techniques to determine the amplitude/intensity of each single frequency • Fourier transformation- Intensity of IR radiation at each frequency determined separately
Recorder/Output •Scanning wavenumber from 400cm-1 to 4000cm-1 • Spectrum of Abs/Trans against frequency/wavenumber is produced
Light Source • Provide IR radiation
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Strength of bond Single, Double, Triple Bonds
Mass of atoms
Lighter/Lower Mass atom • Higher energy frequency for vibration
Stretching Vibration Vs Bending Vibration
IR absorption frequency depends
Heavier/Higher Mass atom • Lower energy/frequency for vibration
Bending Vibration • Less energy needed for resonance • Lower frequency/wavenumber needed
Stretching Vibration • More energy needed to stretch bond • Higher frequency/wavenumber needed
Stronger bond • Higher energy needed for resonance • Higher frequency/wavenumber absorbed
Weaker bond • Lower energy needed for resonance • Lower frequency/wavenumber absorbed
IR absorption frequency
Strong bond
Weak bond
C- H = 2840cm-1
C- CI = 600cm-1
C- H stretch = 2840cm-1
C- H bend = 1400cm-1
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IR spectroscopy for Alcohol Level Detremination
Uses of IR Spectroscopy
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IR Spectroscopy on Alcohol Level Determination
Major absorption for alcohol
• 3230cm-1 – (O-H) stretch
• 2950cm-1 – (C-H) stretch
• 1400cm-1 – (C-H) bend
• 1200cm-1 – (C-O) stretch
• Alcohol concentration cannot be measured from O-H vibration (3230cm-1) due to water vapour present in atmosphere and breath • C-H vibration ( 2950cm-1 ) is used • Propanone, ketone bodies which is produced by diabetic patients also absorb at 2950cm-1 • A second sensor to detect propanone was used. (To eliminate the absorption due to propanone)
Sample cell
Reference cell
Breath sample out Breath sample in Infrared
Intoximeter – Measure the alcohol content in breath
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IR spectroscopy for Functional group Determination
Uses of IR Spectroscopy
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Different bonds absorb IR radiation at frequency/wavenumber . Use IR to identify the bonds and the functional group in a molecule. Common functional groups • (COOH), (O-H), (C=O), (C=C), (C-O), (C-H)
IR spectra of organic compounds with different functional groups
IR Absorption by different types of bonds/functional gps
IR spectrum with different functional gps and fingerprint region
Fingerprinting region • Range from (1500- 400cm -1) • Specific to each molecule
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IR spectra of organic compounds with different functional groups
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Propanal (CH3CH2CHO) • (2840-3000) → C-H stretch • (2720) → C-H stretch of CHO • (1680-1740) → C=O stretch
Hex-1-ene CH2=CH(CH2)3CH3 • (2840-3000) → C-H stretch • (1610-1680) → C-C stretch • (1200- 1400) → C-H bend
Hex-1-yne CH2≡CH(CH2)3CH3 • (3350) → C≡ C stretch • (2840-3000) → C-H stretch • (1200- 1400) → C-H bend
IR spectra of organic compounds with different functional groups
Chloromethane CH3CI • (2840-3000) → C-H stretch • (1200-1400) → C-H bend • (700-800) → C-CI stretch
Halogenoalkane Aldehyde
Alkene Alkyne
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IR spectra of organic compounds with different functional groups
Methanol (CH3OH) • (3230-3550) → O-H stretch Broad Absorption due to H bonding between molecules • (2840-3000) → C-H stretch • (1000-1300) → C-O stretch
Ethanol(CH3CH2OH) • (3230-3550) → O-H stretch Broad Absorption due to H bonding between molecules • (2840-3000) → C-H stretch • (1000-1300) → C-O stretch • (1200- 1400) → C-H bend
Phenol (C6H5OH) • (3230-3550) → O-H stretch Broad Absorption due to H bonding between molecules • (2840-3000) → C-H stretch • (1400-1500) → C=C aromatic stretch • (1000-1300) → C-O stretch
Benzoic acid (C6H5COOH) • (3230-3550) → O-H stretch Broad Absorption due to H bonding between molecules • (2840-3000) → C-H stretch • (1400-1500) → C=C aromatic stretch • (1000-1300) → C-O stretch • (1680-1740) → C=O stretch
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Click here to animated Spectra Click here to search IR spectra
IR Spectra search for different Organic Molecules