Flashcards in IR spectroscopy Deck (31):
IR energy is too low to cause electronic transitions. True or false?
Molecules remain in ground state even after absorbing IR. True or false?
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
At the lower energy end of the spectrum there is a vibration every ____ femto seconds
What are the two types of vibrations?
Stretching and bending
An asymmetrical stretch takes more energy than a symmetrical stretch. True or false?
What are the two types of in-plane bending?
What are the two types of out of plane bending?
Only vibrations that result in net change in polarity of a bond, give rise to IR bands, True or false?
Symmetrical bonds with no dipole moments (e.g. N2, O2) give no IR peaks. True or false?
Symmetrical stretches give no rise to peaks but asymmetrical do. True or false?
In order for IR to be active, a vibration must cause a change in _____ ______ of the molecule
Molecular asymmetry by stretching and/or bending is a requirement for excitation by IR. True or false?
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?
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
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?
Stronger bonds require more energy to vibrate and so are at a higher frequency. True or false?
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?
A primary amine gives a _____ peak with _____ sharp spikes
A secondary amine gives a ______ peak with _____ sharp spike
Alcohol OH bond is a _____ peak
What are the two types of instrumentation for IR spec?
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?
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