Principles of Chemical Analysis ES (5) Flashcards
What is another name for the far UV region?
vacuum UV
What is the far UV region’s wavelength limits?
less than 200 nm
What are the energies involved in spectral transitions in far UV region?
greater than 50,000 cm-1
What are the near ultraviolet regions wavelength limits?
200 - 400 nm
What are the energies involved in the near UV spectral transitions?
50,000 - 25,000 cm-1
What is the UV-A region?
315 - 4000 nm
What is the UV-B region?
280-315 nm
What is the UV-C region?
< 280 nm
What are the wavelength limits of the visible region?
400 - 780 nm
What are the energies involved in the spectral transitions in the visible region?
25,000 - 12,821 cm-1
What is the range of molecular extinction coefficients seen in electronic spectra
5e5 for strongest to <1 for weakest
What is the most probable electronic transition?
HOMO to LUMO
What are the relative energy levels for the different types of transitions?
125 - 650 kJ/mol
What type of bonds do σ bonds form
single
what kind of bonds do pi electrons form
multiple
what kind of bonds do n electrons form
nonbonding using atoms right of C on the table
What is a chromophore?
group of atoms producing an electronic absorption
What are auxochromophores?
substituents that increase intensity or wavelength of principle chromophores
What are some of the typical auxochromophores?
methyl, hydroxyl, alkyl, halogen, amino groups
What is bathochromic shift?
shift in absorption maximum to longer wavelength or lower energy (red shift)
what is a hypsochromic shift?
shift in absorption maximum to shorter wavelength or higher energy (blue shift)
What is a hyper chromic effect?
increase band intensity
What is a hypochromic effect?
decrease in band intensity
In what type of electronic transitions do σ-electrons take part?
σ to σ; n to σ; σ to pi*
In what region the spectrum do σ transition occur?
outside the normal spectral range (far)
In what type of electronic transitions do π-electrons take part?
σ to π; π to π; n to π*
In what region of the spectrum do π transitions occur?
NEAR; alkenes 175 nm and alkynes 120 nm
In what type of electronic transitions do n electrons take part?
n to σ; n to π
In what region of the spectrum do these n transitions occur?
Near UV, far UV, vis
What types of transitions do saturated hydrocarbons undergo?
σ to σ*
What is the effect of unsaturation on electronic absorption spectra?
give rise to the most varied spectra
What happens when functional groups containing n electrons are added tot eh molecule?
n to σ* allows for increased wavelength of σ to σ*
What types of molecules demonstrate the most varied electronic spectra?
unsaturated
