Ultra-Visible Spectroscopy Flashcards
What is a spectrophotometer?
Which is an instruemtent measures transmission or absorbance of light through a sample
UV-Vis light source
deuterium discharge tube for the UV
Tungsten filament lamp for the visible light
Parts of spectrophotometer
Light source
monochromator
beam chopper
sample
detector
amplifier
display
UV Theory
UV-Vis spectroscopy measures the amount of light absorbed at a wavelength ranges of about 100 to 800 nm.
This absorbtion of ultra violet or visisble light by molecules leads to electronic transtions.
Each electronic state in a molecule will contain vibrational states, which contain rotational states.
The Molecular Orbital Model
MO describes covalent bonds in terms of molecular orbitals.
MO are mathemtamical eqautions that describe the region in a molecule where there is a high probability of finding electrons.
Bonding molecular lower in energy than the atomic orbitals from which it is composed.
Antibonding moleculat orbitals (sigma star or pi star) higher in energy than the atomic orbtitlas from wich it is composed
Electronic Molecular Energy Levels
THe most common electronic transitions are:A n —> pi* and pi—> pi*
Functional Groups Effects
The absorbing group in a molecule is called a Chromophore.
The absorbance of a molecule may be altered by a group called an auxochrime.
Conjugated chromophores results in a bathochromic shift or red shift in the absorption spectrum.
Molecules with more then eight conjugated double bonds absorb light in the visible region of the spectrum
HOMO vs LUMO
HOMO is the highest Occupied molecular orbtials
LUMO is the lowest Unoccupied Molecular orbital
Beer’s Law
Absorbanace is proportional to the concentration of light absorbing molecules in the sample.
Spectrophotometric analysis with visible radiation is called Colorimetry.
For a compound to be analyzed by spectrophotomerty it must absorb electromagnetic radiation.
Isobestic Point
Is the point in which the absorbtion of a solution is the same as the other solutions with in the sample. However the absorbance is found by a combination of beers law for each compound
Application of UV
Qualitative analysis: different molecules has different max wlenths
Quantitive analysis we can fix the max wavelneth and measure the absorbance vs concentraion.
Uses of Quantitative analysis of UV
Used in determination of the concentration of organic, inorganic, and biochemical
Used in enevirmonmetal chemesity to determine the concentration of metal ions
HLPC
Two types if UV damaging Rays
UV-A (315-400) UV-B (280-315)
How is sunscreen used to prevent UV light from causing damge to the structure of DNA and what are the two main types.
inorganic and organic
Inorganic sunscreens contain salts like titanium dioxide or zinc oxide. and these salts block and scatter the UV rays.
Organic sunscreens are conjuaged systems that absorb UV rays like a sponge before they can damage your skin
How does bleach work on clothes?
Bleach works by oxidaiozing or reducing a chromophore thus disrupting the conjugation
The changed chromophore molecules either reflect no colour or a colour outside teh visblie spectrum
