Electromagnetic Radiation and Spectroscopy

Radiowaves

Nuclear spin

Nuclear Magnetic Resonance Spectroscopy

• Organic structure determination • MRI and body scanning

Infra Red

Molecular vibration

Infra Red Spectroscopy

UV or visible

Transition of outer most valence electrons

• Organic structure determination • Functional gp determination • Measuring bond strength • Measuring degree unsaturation in fat • 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

• Spectroscopy measures the interaction of the molecules with electromagnetic radiation

• Particles (molecule, ion, atom) can interact/absorb a quantum of light

Picture from: http://www.lpi.usra.edu/education/fieldtrips/2005/activities/ir_spectrum/

Spectroscopy

Electromagnetic

Radiation

Nuclear spin

High Energy Radiation

Gamma/X ray

Transition of inner electrons

UV or visible

Transition of outer most valence electrons

Infra Red

Molecular vibration

Microwave

Molecular rotation

Radiowaves

Low Energy Radiation

Infra Red Spectroscopy Nuclear Magnetic Resonance Spectroscopy

Ultra Violet Spectroscopy

Atomic Absorption Spectroscopy

For a molecule to absorb IR • Vibration within the molecule must cause a net change in dipole moment of molecule

• Frequency of radiation matches the vibrational natural frequency of the molecule, then radiation will be absorbed, causing a change in amplitude of molecular vibration. • A permanent dipole is not necessary, only a change in dipole moment • Not all bond absorb at IR wavelength. For IR absorption a bond must have an electric dipole (bond polarity) that changes as it vibrates. • Molecules absorb IR – cause changes in modes of vibration (stretching/bending)

http://catalog.flatworldknowledge.com/bookhub/4309?e=averill_1.0-ch02_s01

http://chemwiki.ucdavis.edu/Organic_Chemistry/Organic_Chemistry_With_a_Biological_Emphasis/Chapter__4%3A_Structure_Determination_I/Section_4.2%3A__Infrared_spectroscopy

Infrared Spectroscopy and Molecular Vibration

Molecular Vibration

Stretching Mode Bending Mode

Symmetric Stretching • change in bond length • bond become shorter/longer • IR ACTIVE (change in dipole) • IR INACTIVE (No change in dipole)

Asymmetric Stretching • change in bond length • bond become shorter/longer • IR ACTIVE (change in dipole) • IR INACTIVE (No change in dipole)

Symmetric Bending • change in bond angle • bond angle bigger/smaller • IR ACTIVE (change in dipole) • IR INACTIVE (No change in dipole)

Asymmetric Bending • change in bond angle • bond angle bigger/smaller • IR ACTIVE (change in dipole) • IR INACTIVE (No change in dipole)

Diatomic molecule of same element DON’T absorb IR • Symmetrical diatomic bond will not absorb IR • No change in dipole moment as molecule vibrate • No absorption of IR

Dipole change

No change in dipole moment

Molecular Vibration

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 • Absorb IR

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

Diatomic Molecules

Vs

http://backreaction.blogspot.kr/2009/01/water-is-blue-because-water-is-blue.html

http://giantsoftheinfinitesimal.com/goi-education.htm

Molecular Vibration

Stretching Mode Bending Mode

Symmetric Stretching • change in bond length • bond become shorter/longer • change in dipole moment • Absorb IR at 3652 • IR ACTIVE

Asymmetric Stretching • change in bond length

• bond become shorter/longer • change in dipole moment • Absorb IR at 3756 • IR ACTIVE

Symmetric Bending • change in bond angle

• bond angle bigger/smaller • change in dipole moment • Absorb IR at 1595 •IR ACTIVE

Molecular Vibration for Water and IR Spectrum.

IR spectrum for water

http://backreaction.blogspot.kr/2009/01/water-is-blue-because-water-is-blue.html

http://giantsoftheinfinitesimal.com/goi-education.htm

Molecular Vibration

Stretching Mode Bending Mode

Symmetric Stretching • change in bond length • bond become shorter/longer • change in dipole moment • Absorb IR at 1150 • IR ACTIVE

Asymmetric Stretching • change in bond length

• bond become shorter/longer • change in dipole moment • Absorb IR at 1360 • IR ACTIVE

Symmetric Bending • change in bond angle

• bond angle bigger/smaller • change in dipole moment • Absorb IR at 540 •IR ACTIVE

Molecular Vibration for Sulfur Dioxide and IR Spectrum.

IR spectrum for sulfur dioxide

http://backreaction.blogspot.kr/2009/01/water-is-blue-because-water-is-blue.html

http://giantsoftheinfinitesimal.com/goi-education.htm

Molecular Vibration

Stretching Mode Bending Mode

Symmetric Stretching • change in bond length • bond become shorter/longer • Bond polarity cancel out • NO change in dipole moment • IR INACTIVE

Asymmetric Stretching • change in bond length

• bond become shorter/longer • change in dipole moment • Absorb IR at 2349 • IR ACTIVE

Symmetric Bending • change in bond angle

• bond angle bigger/smaller • change in dipole moment • Absorb IR at 667 • IR ACTIVE

Molecular Vibration for Carbon Dioxide and IR Spectrum.

IR spectrum for carbon dioxide

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

Spectra difference between Acid and Ester

Ethyl ethanoate (CH3COOCH2CH3) • (2840-3000) → C-H stretch • (1680-1740) → C=O stretch • (1000-1300) → C-O stretch

Methanoic acid (CH3COOH) • (3230-3550) → O-H stretch • (2840-3000) → C-H stretch • (1000-1300) → C-O stretch • (1680-1740) → C=O stretch

Methanoic acid (CH3COOH) • (3230-3550) → O-H stretch • (2840-3000) → C-H stretch • (1000-1300) → C-O stretch • (1680-1740) → C=O stretch

Methanoic acid

Methanoic acid

Spectra difference between Acid and Alcohol

Methanol (CH3OH) • (3230-3550) → O-H stretch • (2840-3000) → C-H stretch • (1000-1300) → C-O stretch

Ethyl Ethanoate

Methanol

Vs

Vs

Propan -2-ol CH3CH(OH)CH3

Spectra difference between Alcohol and Ketone

Propanone CH3 CO-CH3

Hexan-1-ol CH3(CH2)4CH2OH Hexan-2-one CH3CO(CH2)3CH3

http://chemwiki.ucdavis.edu/Organic_Chemistry/Organic_Chemistry_With_a_Biological_Emphasis/Chapter__4%3A_Structure_Determination_I/Section_4.2%3A__Infrared_spectroscopy

IR spectra of organic compounds with different functional groups

OH

↓

C - H

↓

C - H

↓

C - H

↓

C=O → ← C-H bend

C-H bend →

← C-H bend

C-H bend →

Alcohol Ketone

Vs

Vs

http://chemwiki.ucdavis.edu/Organic_Chemistry/Virtual_Textbook_of_OChem/Spectroscopy/Infrared_Spectroscopy

Match the functional groups with its correct Spectra

2 methylpropanal (Aldehyde) Butan-2-one (Ketone)

2 methylpropen-1-ol ( Alcohol + Alkene) Cyclobutanol (Alcohol)

← C-H stretch

← C-H stretch

← C-H stretch

← C-H stretch

← C=O stretch C=O stretch →

O-H

↓

O-H

↓

← C-H bend

← C-H bend

C-H bend →

C-H bend →

C=C stretch →

Finger printing

region

Finger printing

region

Finger printing

region

Finger printing

region

2 methylpropanal (Aldehyde) Butan-2-one (Ketone) Cyclobutanol (Alcohol) 2 methylpropen-1-ol ( Alcohol + Alkene)

Click here to animated Spectra Click here to search IR spectra

IR Spectra search for different Organic Molecules