ib chemistry on infrared spectroscopy and ir spectra analysis

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%

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Wavenumber, cm-1

Transmittance or Absorbance of IR Spectra

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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

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IR Spectra search for different Organic Molecules