Download - IR and NMR spectroscopy
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Presented by:Asif Mohammad Salehin
Jatan TanchangyaSulov Saha
Md. Mohsin Ali
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SpectroscopyDefinition: Spectroscopy is the study of of the interaction between matter and electromagnetic radiation.
Types of spectroscopy:• Absorption spectroscopy – uses electromagnetic spectra
in which a substance absorbs: IR, NMR
• Emission spectroscopy – uses electromagnetic spectra in which a substance emits: Luminescence
• Scattering spectroscopy – measures the amount of light that a substance scatter at certain wavelengths, incident angles and polarization angles: Raman
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Infrared Spectroscopy
• IR spectroscopy is concerned with the study of absorption of infrared radiation, which causes vibrational transition in the molecule.
• IR spectra mainly used to identify functional groups present in molecules.
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Infrared Molecular vibration
Infrared spectrosco
py
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Principle of IR spectroscopy
• Molecules are made up of atoms linked by chemical bonds. The movement of atoms and the chemical bonds like spring and balls (vibration).
• This characteristic vibration are called Natural frequency of vibration.
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• When energy in the form of infrared radiation is applied then it causes the vibration between the atoms of the molecules and when,
Applied infrared frequency = Natural frequency of vibration
Then, absorption of IR radiation takes place and a peak is
observed.
Different functional groups absorb characteristic frequencies of IR
radiation. Hence gives the characteristic peak value.
Therefore, IR spectrum of a chemical substance is a finger
print of a molecule for its identification.
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Criteria for a compound to absorb IR radiation
• Correct wavelength of radiation A molecule to absorb IR radiation, the natural frequency of vibrations of some part of a molecule is the same as the frequency of incident radiation.
• Change in dipole moment A molecule can only absorb IR radiation when its absorption cause a change in its electric dipole.
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Types of Molecular Vibrations
1.Stretching
Symmetrical
Asymmetrical
2.Bending
In plane
Out plane
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a) Symmetrical stretching:
2 bonds increase or decrease in length simultaneously.
H
H
C
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b) Asymmetrical stretching: In this, one bond length is increased and other is decreased.
H
H
C
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a) In plane bending: i. Scissoring ii. Rocking
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b) Out plane bending:i. Wagging
ii. Twisting
H
H
CC
H
H
CC
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Instrumentation
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Interpreting an Infrared Spectrum
• Ethanoic acid (it contains C-C, C-H, C=O, C-O and O-H bonds.)
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Fig: IR Spectra of common functional groups
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Applications• Identification of functional group and structure
elucidation• Identification of substances• Studying the progress of the reaction• Detection of impurities• Quantitative analysis
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Pros and Cons of IR Spectroscopy
Largely qualitative Difficult to analyze complex solutions in infraredSimilar infrared spectra can misidentify the fingerprint region
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NMR Spectroscopy
The study of absorption of radiofrequency
radiation by nuclei in a magnetic field is called
Nuclear Magnetic Resonance.
• NMR spectroscopy is commonly used technique for organic compound structure determination.
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Radiowaves
Nuclear spin
NMR spectrosco
py
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Principle of NMR spectroscopy
• A spinning charge creates a magnetic moment, so these nuclei can be thought of as tiny magnets.
• If we place these nuclei in a magnetic field, they can line up with or against the field by spinning clockwise or counter clockwise.
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NMR active nuclei
Number of nucleons-Must be odd for residual magnetism For e.g. Hydrogen exhibits, Deuterium does not1H, 13C and 15N nuclei-have a very small magnetic moment: “half integer spin”
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Resonance condition
• Transition from low to high energy state occurs
• hע = gßH
• Either a constant magnetic field is applied and appropriate region of radio frequency is swept
• Or a constant frequency is employed & the external magnetic field is swept
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Chemical shifts- Arises from applied field inducing secondary fields at the proton by interacting with adjacent bonding electrons- Is measured in ppm relative to an internal standard – TMS- Trimethylsilane (TMS) is the accepted internal standard for calibrating chemical shift for 1H, 13C and 29Si NMR spectroscopy in organic solvents.
H
3.6 ppm
1.2 ppm
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Splitting or MultiplicityScalar coupling constants- Protons on adjacent carbons will interact and “split” each others resonances into multiple peaks (multiplets)- Measured in Hz (“Hertz”, s-1) - Caused by different spin states of neighboring spins (parallel or antiparallel)
H
- Equivalent protons do not show spin-spin coupling- Doublet: 1 coupling partner- Triplet: 2 coupling partners- Quartet: 3 coupling partners
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When energy in the form of radiofrequency is applied
When applied frequency is equal to processional frequency
Absorption of energy occurs
Nucleus is in resonance
NMR signal is recorded
Steps involved in the process
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Instrumentation
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• Fourier Transform NMR Instrument
• Continuous Wave NMR Instrument
Two types of NMR spectroscopy instruments
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1H NMR Spectroscopy
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Study of 1H NMR Spectra
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13C NMR Spectroscopy
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Interpretation of NMR Spectrum
Number of main signal = number of equivalent protons in unknown compound
Chemical shift indicates the type of H atoms. E.g. methylene, methyl groups, etc.
Spin-spin splitting ---- arrangement of groups in the molecule.
Area of peaks ---- no. of H nuclei present in each group. For e.g. relative areas of methyl peaks in propane would be 6:2. In butane it would be 6:4
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E.g. of ethanola) Low resolution spectrum b) High resolution
spectrum
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Applications• To study molecular structure and interactions• For determining 3D structure of proteins and
other macromolecules• Solid-state NMR is used to study variety of
materials• Magnetic Resonance Imaging (MRI)• Oil and natural gas exploration • Polymer production, cosmetics and food
manufacturing
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ppm
H2O
Protein NMR
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MRI
Eliminates risk of X-radiation
Excellent and contrast resolution
Detecting disease at earlier stages
Magnetic resonance imaging (MRI) is a noninvasive medical test that physicians use to diagnose and treat medical conditions.
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Pros and Cons of NMR Spectroscopy
Provides high resolution informationDoes not require a protein crystal and is not affected by crystal contactsCan be used to study flexible proteinsReflects conformational averaging
Requires high concentrations of soluble proteinCan not be applied to large proteins (800kD max so far)Can not be used with amyloid fibrils
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