EMR/UV-Vis Flashcards
Light waves are electromagnetic. True or false?
True
How is the speed of light calculated?
Wavelength x frequency
On absorption of radiation, electrons are promoted from a low energy state to a higher energy (excited state). True or false?
True
EMR is produced when excited particles return to lower-energy levels or the ground state. True or false?
True
Excitation of a molecule can be electronic, rotational or vibrational. True or false?
True
What is on the y and x axis of UV-Vis spectrums?
y - absorbance
x - wavelength
Most drugs, with the exception of _______ ones absorb UV light
coloured
Why is the UV-vis spectrum broad rather than sharp?
Because photons with slight difference in energy can still cause electronic transitions from exciting electrons from the many vibrational states
What are the three types of orbitals?
sigma
pi
n - non-bonding
When a bonding orbital is created, there is also an anti-bonding orbital created that is normally unoccupied but lies at a higher or lower state?
Higher (less stable) state
On energy level diagram, jumps from which two states are in low enough energy for pharmaceutical analysis?
pi to pi*
and n to pi*
> 200nm absorption is most common for pharmaceutical analysis. True or false?
True
What are the 3 uses of UV absorption?
Identification of drugs - by comparing spectra
Measuring reactions, ionisation
Quantification of drugs - most useful
UV absorption is mostly restricted to drug molecules with conjugated bonds. True or false?
True
What is meant by a conjugated structure?
Double bonds alternating with single bonds
Conjugated structures tend to shift absorption to a shorter wavelength. True or false?
False - longer wavelength
What is meant by a bathochromic shift?
shift to a longer wavelength
The longer the conjugated system, the less separation in energy levels and therefore the longer the wavelength. True or false?
True
Bathochromic is a red shift. True or false?
True
What colour is associated with a hypsochromic shift?
Blue
Why does conjugation shift the wavelength to red?
Because in conjugated systems, electrons are easily delocalised, making energy gaps between orbitals smaller, therefore lowering the energy needed to excite them
What is an auxochrome?
A functional group containing lone pair(s) of electrons that do not absorb appreciable amounts of UV on its own but shifts peaks to longer wavelength and makes the peak higher intensity
What is a chromophore?
Part of the molecule that absorbs UV or visible light
The amount of light absorbed is dependent on the concentration of a sample. True or false?
True
What is the equation for the Beer lambert law?
A = Ebc E = molar absorptivity (absorbance of 1M solution) b = path length of cell in cm c = conc in mol/l
What does the beer lambert law apply?
A linear relationshop between absorbance and concentration. However, in reality, this is only true if A > 1.5
In the beer lambert law, what assumptions apply for absorbance to be directly proportional to concentration?
Incidence radiation must be monochromatic
absorbance checks can be made against standards such as potassium dichromate
each molecule in solution acts as an independent absorbing species
absorption takes place in a homogenous solution
