IR spectroscopy Flashcards
IR energy is too low to cause electronic transitions. True or false?
True
Molecules remain in ground state even after absorbing IR. True or false?
True
What is on the x and y axis of IR spectrums?
y - % transmittance
x - wavenumber
At the higher energy end of the spectrum, there is a vibration every ____ femto seconds
8
At the lower energy end of the spectrum there is a vibration every ____ femto seconds
50
What are the two types of vibrations?
Stretching and bending
An asymmetrical stretch takes more energy than a symmetrical stretch. True or false?
True
What are the two types of in-plane bending?
Scissoring
Rocking
What are the two types of out of plane bending?
Wagging
Twisting
Only vibrations that result in net change in polarity of a bond, give rise to IR bands, True or false?
True
Symmetrical bonds with no dipole moments (e.g. N2, O2) give no IR peaks. True or false?
True
Symmetrical stretches give no rise to peaks but asymmetrical do. True or false?
True
In order for IR to be active, a vibration must cause a change in _____ ______ of the molecule
dipole moment
Molecular asymmetry by stretching and/or bending is a requirement for excitation by IR. True or false?
True
A molecule has dipole moment if?
The centre of positive charge is different to the centre of negative charge
Dipole moment = separation x charge. True or false?
True
How does dipole moment affect intensity of absorption?
The bigger the electronegativity difference, the greater the dipole moment and the higher the intensity
The absorption of IR for a given bond depends on what 3 things?
the mass of the atom connected to the bond
strength of the bond
dipole moment
Why does the mass of an atom connected to the bond have an effect on absorption of IR?
Because heavier atoms make it harder to stretch the bond
Stretching requires less energy than bending. True or false?
False
Stronger bonds require more energy to vibrate and so are at a higher frequency. True or false?
True
What are the uses of IR spectroscopy?
Identification of bonds
Obtain structural information about functional groups of drug molecule
Detecting polymorphs of drugs
Complete structure of drug can be assigned from IR. True or false?
False
A primary amine gives a _____ peak with _____ sharp spikes
broad
two
A secondary amine gives a ______ peak with _____ sharp spike
broad
one
Alcohol OH bond is a _____ peak
rounded
What are the two types of instrumentation for IR spec?
Dispersive instrument
Fourier Transform instrument
The cells in the dispersive instrument have to be made of a certain material which are inactive in the region. True or false?
True
For non-aqueous samples, what cell types are used?
KBr, NaCl, CaF2
For aqueous samples, what cell types are used?
non-hygroscopic material - diamond, AgCl
What are the applications of near IR (NIR)?
Quality control, particle size i.e. physical properties of formulation
