UV spectroscopy Flashcards
What is a chromophore?
A covalently unsaturated group responsible for electronic absorption.
What is an auxochrome?
A saturated group with nonbonded electrons.
What happens when an auxochrome is attached to a chromophore?
It can increase the wavelength and the intensity of absorption of the UV rays.
What is a bathochromic shift?
When the maximum absorption gets shifted to a longer wavelength.
What is a hypsochromic shift?
When the maximum absorption gets shifted to a shorter wavelength.
What is the hyperchromic effect?
An increase in absorption intensity.
What is the hypochromic effect?
A decrease in absorption intensity.
How do you calculate wavenumber?
wavenumber = 1/wavelength
How do you calculate velocity?
velocity = frequency x wavelength
How do you calculate absorbance?
absorbance = lg ( incident light / transmitted light)
OR
absorbance = lg (1/ transmittance)
What is molar absorptivity?
The absorbance at a particular wavelength of a 1 mol/l solution in a 1cm cell.
What is the equation for Beer - Lambert law?
Absorbance = molar absorptivity x path length x concentration of solute in mol/l
OR
Absorbance = specific absorbance x path length x concentration of solute in g/100ml
What is path length?
The distance the light travels through the sample.
What is specific absorbance?
The absorbance of a 1g/100ml solution in a 1cm cell
What is the relationship between absorbance and concentration according to the Beer-Lambert law?
They have a linear relationship
How does conjugation affect the wavelength of maximum absorption?
More conjugation = greater wavelength
What is lambda max?
The wavelength at which a substance has its strongest photon absorption
What does the reference cell contain?
Pure solvent (so it doesn’t absorb a significant amount of light in the interested range)
What is the relationship between wavelength, frequency and energy?
Higher wavelength = lower frequency = lower energy
What is a homoannular and heteroannular diene?
Homoannular: both double bonds present in the same ring
Heteroannular: the double bonds are present in 2 different rings
What is one property of the chemicals present in sunscreens?
They are highly conjugated so they can absorb UV, preventing it from getting into the skin
