experimental determination of structure 3

Question 1

some atomic nuclei can spin about their own axes. give an exaple

Answer 1

eg the 1H nucleus (hydrogen nucleus or proton) can spin clockwise or anticlockwise. as a result protons behave as tiny magnets and when placed between the poles of a powerful magnet, some align themselves with the field of the magnet , whilst others align against it

Question 2

protons aligned with the field have a slightly _____ energy than those aligned against it

Answer 2

lower

Question 3

what does the energy difference between the two states ( hydrogen nucleus aligned against or with external magnetic field) correspond to

Answer 3

corresponds to the radio frequency region of the electromagnetic spectrum

Question 4

how does nmr work

Answer 4

1h nuclei behave like magnets, when placed in a magnetic field they can align themselves with or against. those with the field are of lower energy than those against. when radio waves energy is absorbed to promote those in the lower energy state to the higher energy state.
- as they fall back down to lower energy they emit radiation which can be detected and plotted on a spectrum

Question 5

as protons fall back into a lower energy state, what happens?

Answer 5

the same radio frequency that was absorbed is emitted

Question 6

how can the frequency emitted be measured

Answer 6

with a radio receiver , this is known as h NMR

Question 7

low resolution H NMR spectroscopy - what does it give info on

Answer 7

H NMR gives info on

• how many different chemical environments the protons in an organic molecule can exist in
• how many protons are in these environments
• the type of proton environment

Question 8

explain the protons in their specific chemical environments : ethanol

Answer 8

pg 78 brightred

Question 9

what is the small peak called TMS

Answer 9

TMS Is used as a standard against which all absorptions due to other proton environments are measured

Question 10

value of TMS (tetramethylsilane)

Answer 10

zero

Question 11

what is chemical shift
symbol
units

Answer 11

difference between protons in TMS and protons in other chemical environments

• ppm

Question 12

where can chemical shift values be found

Answer 12

data booklet ( proton NMR spectra correlation chart)

Question 13

how are high resolution / low resolution nmr spectra obtained

Answer 13

• high resolution is obtained using radio frequency of 300-500MHz (results in more detailed spectra being produced
• low resolution 90-200MHz

Question 14

what extra detail does high resolution nmr show

Answer 14

each peak can be seen in more detail and it can be seen that they are made up of multiple peaks called multiplets

Question 15

how can there be more than one peak in a given proton environment

Answer 15

• there are hydrogen atoms within that environment that are experiencing slightly different magnetic fields - these differences in chemical shift are due to the influence of the hydrogen atoms on the neighboring carbon atoms

Question 16

the splitting of the peaks into a set of more peaks is called ….

Answer 16

spin-spin splitting pattern

Question 17

analysing multiplets allows the neighboring proton environment to be identified , how can this be done

Answer 17

the splitting pattern follows the n+1 rule

• n is number of hydrogens attached to the next door carbon atom
• n+1 will be the number of peaks that will be seen in the cluster

Question 18

name of multiplet , n+1(number of peaks) and (n) number of h atoms on the next door atom

Answer 18

singlet - n+1= 1 , n=0
doublet n+1 + 2 , n=1
triplet n+1 = 3 n=2
quartet n+1 =4 n=3