Proton NMR Flashcards
1
Q
Why is proton NMR used over 13C NMR?
A
- nearly all hydrogen atoms are `1H
- So it is easier to get a spectrum
2
Q
What causes the hydrogen atoms to resonate at different frequencies?
A
- different functional groups
- nuclei with more electrons around them are more shielded
3
Q
What is significant about the size of the peak>
A
- areas under the peak are proportional to the number of hydrogen atoms in that environment
4
Q
WHat effects the size of the chemical shift value?
A
- further away a hydrogen atom is from an electronegative atom, the smaller its chemical shift
5
Q
What is the intergration trace?
A
- area under curve proportional to number of hydrogen atoms producing
- can be difficult to evaluate by eye, so the instrument produces a line called an intergration trace
- the relative heights of the steps of this trace give the relative number of each type of hydrogen
6
Q
What does the chemical shift value show?
A
- tells you about its environment - the type of functional group it is part of
7
Q
What is the structure of TMS? What is TMS?
A
- tetramethylsilane, Si(CH4)4
- chemical shift value for these hydrogen atoms is zero by definition
#
8
Q
How is the spectrum calibrated>
A
- liquid TMS added to samples before NMR run
- give a peak at a δ value of zero ppm
- modern techniques do not require this
9
Q
What are the other reasons for using TMS?
A
- inert
- non-toxic
- easy to remove from the sample
