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IB Chemistry on Infrared Spectroscopy and IR Spectra analysis
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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
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
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
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
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
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
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
IR spectroscopy for Alcohol Level Detremination
Uses of IR Spectroscopy
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
IR spectroscopy for Functional group Determination
Uses of IR Spectroscopy
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
IR spectra of organic compounds with different functional groups
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
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
Click here to animated Spectra Click here to search IR spectra
IR Spectra search for different Organic Molecules