absorption of radiation = to energy between electron transitions
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Absorption spectra
produces peaks when the compound absorbs rad
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transmission spectra
produces troughs when the sample absorbs rad
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Methods in spectrometry
1. single beam 2. double beam
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single beam method
rad source. monochromator, sample, detector , computer . the detector detects the diff in rad between the sample and the intial rad
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double beam method
after monochromator there is a splitter - splits into 2 beams - 1 travels to sample, the other to a control. detector analyses diff between sample and control
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Chromophore
part of molecule which is responsible for colour/ part of molecule which absorbs Uv
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in electronic spec a wavelength above what is considered visble
>400nm
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peaks in the electronic spectra indicate that the sample is
a uv active compound in solution
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process for sampling
make sample of low conc, such that Absorb< 1
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Beers law
A=Ebc
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absorbance =
-logT
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T =
P/Po
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beers law states that
linear absorbance is directly proportional to conc , untill conc gets too large then not directly prop
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normally WL < X cannot be seen
190nm
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a wl of 20nm requires
vacuum uv spec
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n--> sigma *
OHs
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pi--pi*
alkenes
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n--> pi *
carbonyls
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adjacent chromophores
exist as the same chromophore , due to conjugation- therefore will only produce 1 peak
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adjacent chromophores cause red shift by
reducing energy pi-pi* and n-pi* transitions
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if all atoms are planar then
there is overlap between p orbitals
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how to reduce conjugation
rotate single bond
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auxochromes
any group which is next to a chromophore which increases its max WL
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which molecule absorbs at longer WL
look for lowest energy absorbs at
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what type of molecules increase red shift
polycyclics and hetercycles
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IR spec - absorption due to
bending and stretching of bonds
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which type of bonds vibrate at higher wave no
shorter bonds ie double/triple
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what type of bonds vibrate at lower WN
single - i
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molecules with what mass vibrate at higher WN
low mass
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Other cards in this set
Card 2
Front
how does UV spec work
Back
absorption of radiation = to energy between electron transitions
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