Ch.17 Specroscopy

molecular ion peak (M^+) will be the clear peak at the highest m/z value

a small peak after the M^+ peak that occurs due to small percentages of other isotopes

when molecular ions break down into fragments produces a + charged ion and a chargless radical the other peaks on a mass spectrum are the fragment ions

the IR gets absorbed by the covalent bonds they can vibrate in 2 ways . stretch - distance between the 2 atom increases and decreases in a straight line . bend - bond angle changes heavier atoms vibrate slower stronger bonds vibrate faster

used to identify functional groups in organic molecules IR is passed through the sample molecule absorbs some frequencies emerging beam of light is analysed to identify frequencies absorbed each peak (dip) in the graph is related to a particular bond in the molecule

under 1500 cm-1 can be used to determine the molecule however difficult to determine without computer above 1500 cm-1 clearer

3200-3600

1630-1820

2500-3300

monitor gasses from car exhausts and Breathalyzers to measure ethanol

IR travels through atmosphere and gasses do not absorb as they don’t have the same frequency as the natural bond frequency most is absorbed by the earths surface but some IR is re emitted as longer-wavelength IR which is absorbed by the gasses increasing there vibrations re emmitingf energy in the form of heat

elemental analysis - % comp data to determine empirical formula mass spectrometry - molecular ion peaks to determine mr and fragment ions to identify sections infrared spectroscopy - absorption peaks on an infrared spectrum to identify bonds and functional groups