IR spectroscopy (+ mass spectrometry)

compare the e^- process, types of compounds and method of the 2 types of ionisation techniques in mass spectrometry:

compare the type of mass spectrometer, resolution of Mr and what this shows of the 2 types of mass spectrometry:

electron impact, electrospray (respectively)

why is it useful to have Mr s at high resolutions?

some compounds w/ diff molecular formulae may have the same Mr at a low resolution but different Mr s at a high resolution

what are the different types of bond vibration?

• stretching (symmetric/assymetric)

• bending

what does the frequency at which bonds vibrate at depend on?

• mass of atoms

• bond strength

• type of vibration in bond

how does infreread (IR) spectroscopy work?

• vibrating bonds can absorb radiation at the same frequency as the bond vibration - for organic molecules, the radiation lies in the IR region of the EM spectrum

• when the molecules absorb IR radiation, the degree of stretching/bending increases, meaning the bonds absorb specific frequencies when IR radiation is passed through them

• this allows an IR absorption spectrum to be formed

what are wavenumbers? how can they be calculated?

• used as a measure of the freq of the absorption\

• measured in cm^-1

what is a wavenumber above 1500 cm^-1 used for?

to identify functional groups

what is a wavenumber below 1500 cm^-1 used for?

fingerprinting

what is the ‘fingerprint’ section and what is its significance?

• part of the spectrum which is unique for every molecule

• allows identification of a molecule by comparison of spectra

• can be used to check for impurities as extra peaks in this region indicate the presence of impurities

which functional group does this peak indicate?

alcohol -OH

which functional group does this peak indicate?

C=O (carbonyl)

which two functional groups do these peaks indicate?

respectively:

• acid -OH

• C=O

• (→ carboxylic acid)

which functional group does this peak indicate?

C=C