polymers of life

How does mass spec work

an organic compound is bombarded with electrons causing it to break up into different fragments some of these fragment are charge ions and are picked up by a mass spec and create a fragmentation pattern

what happens with the fragmentation pattern

the pattern is recorded on a mass spec with the mass/charge ion on the x axis and the abundance of each ion on the y axis

what does the fragmentation pattern tell us

can be used to determine the structure

if the charge of the fragment is +1 it will be equal to the mass of the fragment

what does the largest peak mean

the largest peak is the molecular mass of the whole organic molecule

what is the M+1 peak

the peak caused by the small proportion of organic molecules in a sample with cause carbon-13

what could peaks higher than M+1 mean

depend on isotopes in a compound

for example chlorine has to isotopes of 35Cl and 37Cl

what doesn’t mass spec detect

uncharged particles and particles that are two unstable and break down to quickly

how do you find the ‘lost fragments‘

by looking at the difference between two peaks and subtracting the smaller one from the bigger one

(Remember this wont have a charge)

what is different about high resolution mass spec

m/z values are given to 4 or more decimal places

why is high resolution mass spec useful

allows you to compare elements with similar Mrs as only carbon 12 is a whole number

or when several different molecules could have caused the same peak

how would you lay out mass spec in the exam

what is nuclear magnetic resonance (NMR) spectra

an analytical technique used to work out the structure

• a sample of the compound is exposed to to a range of frequencies and wave lengths

• how much is absorbed depends on the environment its in

• the pattern can tell you about where it is

what happens to carbon in different environments

a nucleus is partly shielded from the radiation depending on what is around it so it absorbs different frequency

to be in the same environments carbons must be bonded to the same things in the entire molecule

what does the number of peaks tell you

the number of carbon environments there is

what is the chemical shift used for

to show what carbon environments there is

how would i show this in an exam

• a grid with one row for the type of environment and another for the ppm

• Write the number of carbons and the number of peaks

• write about symmetry (if there is 4 carbons and two carbon enviroments)

what 4 things do we look for in proton NMR (H1 NMR)

• number of peaks=number of H environments’

• ratio of peak areas (relative intensity)= number of H in each environment

• chemical shift value = type of H environment

• splitting pattern = number of H on next door carbon

what is splitting

tells us how many hydrogens are on the neighbouring carbon

O-H don’t get split or cause splitting

how would i show HNMR in and exam

• relative intensity

• type of environment

• ppm

• splitting

• coupled to