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Introduction To Spectros

Spectroscopy is the study of matter through its interaction with electromagnetic radiation. It provides information about molecular structure by observing transitions between different energy levels. Common spectroscopic techniques include UV-Vis, IR, NMR, and MS. Each technique uses a different type and frequency of radiation to probe different properties of molecules such as functional groups, complexity, and quantities of atoms. Interpreting spectroscopic data requires an understanding of the underlying theory and instrumentation for each method.

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Joseph Ong
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176 views12 pages

Introduction To Spectros

Spectroscopy is the study of matter through its interaction with electromagnetic radiation. It provides information about molecular structure by observing transitions between different energy levels. Common spectroscopic techniques include UV-Vis, IR, NMR, and MS. Each technique uses a different type and frequency of radiation to probe different properties of molecules such as functional groups, complexity, and quantities of atoms. Interpreting spectroscopic data requires an understanding of the underlying theory and instrumentation for each method.

Uploaded by

Joseph Ong
Copyright
© Attribution Non-Commercial (BY-NC)
We take content rights seriously. If you suspect this is your content, claim it here.
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Chapter 1

Introduction to Spectroscopy
What is spectroscopy?
• Latin “spectron” : ghost or spirit
Greek “σκοπειν” : to see
• the study of properties of matter through its interaction
(absorption, emission, or scattering) with the different
frequency component of the electromagnetic
spectrum
Units

 Wavelength (l) in cm, m, nm


 Frequency in reciprocal seconds, s-1 or Hz
(1 s-1 = 1 Hz)
 Wavenumber in reciprocal meters, m-1
 Energy in joules, J or kcal

E=hu where C = energy in joules


h = Planck’s constant,
E=hc/l 6.63 x 10-34 J s
• With light, you aren’t looking directly at the molecule—the
matter—but its “ghost.” You observe the light’s interaction
with different degrees of freedom of the molecule.

• Each type of spectroscopy—different light frequency—gives


a different picture → the spectrum.

• Spectroscopy is a general methodology: can be


adapted in many ways to extract the information you need
(energies of electronic, vibrational, rotational states,
structure and symmetry of molecules, dynamic information)
Applications in Structure Elucidation

Radiation & Effect Information Deduced


on the Molecule

UV (190-400 nm);  Extent of p electron systems


VIS (400-800 nm)
 Presence of conjugated
- Changes in electronic multiple bonds
energy levels within the
molecule  Conjugation with nonbonding
electrons
Applications in Structure Elucidation

Radiation & Effect Information Deduced


on the Molecule

IR (MID IR) (400-4000


cm-1; 2.5-25 um)
 Detection of functional groups
-Changes in the with specific vibration
vibrational and rotational frequencies
movements of the
molecule
Applications in Structure Elucidation

Radiation & Effect Information Deduced


on the Molecule

Microwave (9.5 x 109 Hz)  Detection of free radicals


and the interaction of the
- Electronic spin electron with nearby
resonance or electron protons
paramagnetic resonance
induces changes in
magnetic properties of
unpaired electrons
Applications in Structure Elucidation

Radiation & Effect Information Deduced


on the Molecule
Radiofrequency (60-600
MHz)  Detection and quantity of
hydrogen and carbon
- Nuclear magnetic atoms in different
resonance induces environments
changes in the magnetic
properties of certain
atomic nuclei, notably
that of 1H and the 13C
isotopes
Applications in Structure Elucidation

Radiation & Effect Information Deduced


on the Molecule

Electron beam impact  Determination of molecular


(70 eV, 6000 kJ/mol) mass and deduction of
molecular structures from
- Ionization and the fragments produced
fragmentation of the
molecule into a
spectrum of fragment
ions
Essential Features in Instrumentation

 Source of radiation
 Sample holder
 Frequency analyzer (for UV,IR,NMR);
mass analyzer (for MS)
 Detector
 Recorder
Comparison among the spectroscopic methods
UV-Vis IR NMR MS

Identifies functional group + +++ ++ ++

Measures complexity + + ++ +++

Sensitivity (sample size required) +++ +++ + +++

Quantitative information +++ ++ ++ +

Interpretability of data + ++ +++ +

Theory needed to interpret spectra ++ +++ + ++

Ease of instrument operation +++ +++ ++ +

Instrument cost, running cost +++ +++ ++ +

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