Interpreting NMR

Question 1

What happens to the chemical shift of hydrogens next to electronegative atoms?

Answer 1

1. electronegative atoms pull electron density towards then
2. this reduces the electron density around the hydrogen atoms nearby
3. the hydrogens are less shielded
4. they will have a higher ppm

Question 2

In proton NMR what are the 3 kinds of data we must consider?

Answer 2

1. chemical shift data
2. integrals
3. coupling

Question 3

What does chemical shift data tell us about?

Answer 3

what types of protons we have

Question 4

What do integrals tell us about?

Answer 4

the ratios of each kind of proton in the sample

Question 5

What does coupling tell us?

Answer 5

about the protons near to our proton of interest

Question 6

What happens if there is an element of symmetry in a molecule?

Answer 6

the symmetric atoms are chemically equivalent and also CHEMICAL SHIFT equivalent

Question 7

What is the rule for splitting?

Answer 7

if a proton has n neighbouring protons that are equivalent - that proton will be split into n+1 lines

Question 8

When do protons NOT split each other?

Answer 8

when two protons appear at the same chemical shift
for example, in EtBr, (CH3CH2Br), each proton of the CH3 group is ONLY coupled to the protons of the CH2 group, not the other CH3 protons because they all come at the same chemical shift!