IR spectroscopy and mass spectroscopy

covalent bonds in molecules….

possess energy and vibrate naturally about a central point

stretch (type of covalent bond vibration)

rhythmic movement along line between atoms so that distance betweeen 2 atomic centres increases and decreases

bend (type of covalent bond vibration)

results in a change in bond angle

how does mass of atoms in a bond affect strecthing and bending

heavier atoms vibrate more slowly than lighter atoms

how does bond strength affect stretching and bending

stronger bonds vibrate faster than weaker bonds

how does ir radiation affect covalent bonds

makes them bend and stretch more

what type of radiation can bonds absorb

radiation with same frequency as natural bond frequency

how IR spectroscopy happens

beam of IR in range 200-4000cm^-1 passed through sample in spectrometer, molecule absorbs some IR frequencies, emerging beam analysed to identify frequencies absorbed by the sample

fingerprint region (below 1500cm^-1)

unique for every compound, can be used to check if compound is pure

identifying pollutants with IR spectroscopy

uses IR spectral fingerprints which are analysed by remote sensors, measure co2, co and hc emissions, helps monitor localised pollution

breathalysers using IR spectroscopy

pass IR beam through captured breath, characteristic ethanol bonds detected, more IR absorbed=higher reading=more alc in breath

sequence when identifying unknown compound

elemental analysis with percentage composition, mass spectrometry, IR spectroscopy

how does mass spectrometry work

sample vapourised, high energy fast moving es knock es out of sample to form +ve ions, electric field accelerates +ve ions to contant speed, magnetic field deflects charged ions (deflection depends on mass of ions)

relative intensity in mass spectrometry

height of peaks in mass spectrum, shows abundance of ions of each mass

meaning of m/z in mass spectrometry

mass/charge, assume it is same as mr because most ions have 1+ charge

bease peak in mass spectrometry

tallest peak with relative intensity at 100%, usually most stable ion formed

m+1 peak in mass spectrometry

molecular ion with mass 1 unit heavier than normal molecular ion, caused by presence of carbon-13 isotope with 1.1% abundance