Bao cao UV/VIs

Group 5
Chapter 9
Ultraviolet and visible absorption
spectrocopy
Content
UV /Vis spectral region
The UV/Vis spectrum
Electronic transition of organic compound
Chromophore groups
Solvent effects: Solvatochromism
Fieser – Woodward rules
Instrumentation in the UV/Visible
UV/Vis Spectrophotometer
Quantitative analysis: law of molecules obsorption
Methods in quantitative analysis
UV /Vis spectral region
UV /Vis spectral region

Violet:   400 - 420 nm

Indigo:   420 - 440 nm

Blue:   440 - 490 nm

Green:   490 - 570 nm

Yellow:   570 - 585 nm

Orange:   585 - 620 nm

Red:   620 - 780 nm

The UV/Vis spectrum

Transmittance (T)
The transmittance (T) is a fraction of incident rations transmitted by the solution.
T = I / I0
I: Transmitted light
I0: Incident light
T is often expressed as percentage
%T = I / Io x 100

The UV/Vis spectrum

Absorbance: (A)

Is the logarithmic ratio of intensity of incident light to that of transmitted light
A = log Io/ I
A = - log 10 T
It is also known as optical density (O.D.)


Electronic transition of organic compound


Electronic transition of organic compound

There are several types of electronic transitions available to a molecule including:
σ to σ* (alkanes)
σ to π * (carbonyl compounds)
π to π* (alkenes, carbonyl compounds, alkynes, azo compounds)
ή to σ * (oxygen, nitrogen, sulfur, and halogen compounds)
ή to π * (carbonyl compounds)

Example
Chromophore groups

Chromophore: A covalently unsaturated group responsible for electronic absorption. Or Any group of atoms that absorbs light whether or not a color is thereby produced. Eg C=C, C=O, NO2, amine.
There are two types of chromophore
Independent chromophore: single chromophore is sufficient to import color to the compound eg. Azo group
Dependent chromophore: When more then one chromophore is required to produce color. Eg acetone having 1 kentone group is colorless where as diacetyl having two kentone group is yellow

Chromophore groups

Conjugated chromophore system

Azo Compound