WM3: Infrared Spec. Flashcards
Why do molecules absorb only specific frequencies of IR radiation?
Energy is quantised, molecules take a set value of definitive energies rather than the ability to have any energy.
Why do molecules absorb infrared radiation?
It makes the bonds vibrate and stretch
What is the equation that links speed of light, frequency and wavelength?
speed of light = frequency x wavelength
What is the equation that links energy, plancks constant and frequency?
energy = plancks constant x frequency
Where do you find the IR frequencies of molecules?
Data sheet!
What region is called the finger print region?
1500cm-1 to 600cm-1
Why is the finger print region important?
It is a complex region where it is difficult to assign specific bonds but is unique to each molecule!
How would you calculate the wavenumber
1/wavelength in cm
What would you expect to see for butane?
Strong absorption between 2850-2950
What would you expect to see for methylbenzene?
Peaks at above 3000 for the benzene ring, peaks just below 3000 for the methyl group, absorption pattern around 700 typical of a mono-substituted benzene ring
Why do we usually use IR with other spectroscopic techniques?
Gives us a variety of evidence for structure beyond functional groups present
e.g.
Mass spectrum - mass
NMR - C and H environments
