Lecture 1 Proton NMR Flashcards
What does NMR stand for
Nuclear magnetic Resonance
What is NMR
analysing a nucleus within a molecule
What does NMR generate
A magnetic field
are all nuclei NMR active
No
Each nuclei in a molecule can behave differently what are the two ways ?
observed independently and identified
What type of molecules are the most useful for NMR
organic molecules
How does a proton behave
as a tiny magnet
How do protons react in a magnetic field
they align 50/50 paralell and antiparalel
Which proton has the most energy out of parallel and antiparallel and why?
Antiparallel -its less stable
What is the equation including Btotal
πΈ=βπ_π βπΎ/2π π_πππ‘ππ
When shining a light to a proton what happens
The sign of the proton can flip
Why do protons absorb the EMR at different wavelengths
Because each proton experiences a specific magnetic field
What 3 components composes Btotal
B0 Be and Bn
Equation for Btotal
(π΅_πππ‘ππ) =π΅0βπ΅πΒ±π΅π
Whats B0
magnetic field applied by instrument
Whatβs B e
Opposing magnetic field created by circulating electrons around nucleus. It reduces the magnetic field experienced by the protons, hence the negative sign.
Whatβs Bn
As neighbouring protons behave like magnets, they generate their magnetic field Bn that is felt by the considered proton. It can increase or decrease the overall intensity B, hence the Β± sign.
What is sigma
shielding constant
What would be the Btotal of a naked nucleus and why
zero because there is no electrons and no neighbours
Why does sigma vary
due to resonance and inductive effects
If theres an EDG inductive effect on a proton this means
Thereβs an increase in electron density therefore sigma will increase . The proton is shielded
What is spin spin coupling responsible for
for the shape of the signals
Whatβs the word used to describe the shape of the signals
Multiplicity
What does parallel pairing do to the magnetic field
adds to it increasing btotal
What does antiparallel pairing do to the magnetic field
Bo-Be decreases
What causes the addititve and subtractive effects on spin coupling
orientation
