O- NMR Flashcards
1
Q
What is chemical shift and what are its units?
A
- diff in freq betw resonating nucleus + TMS
- parts per million (ppm)
2
Q
Why do hydrogen atoms attached to different functional groups feel the magnetic field differently?
A
- nuclei shielded by diff no. of e-
3
Q
What does area under peaks (resonances) show on a NMR spectrum?
A
area ∝ no. of H atoms
4
Q
What does TMS stand for?
A
tetramethylsilane, Si(CH3)4
5
Q
Why is TMS used as a standard for chemical shift?
A
- δ value = 0ppm - calibrate spectrum (also x interfere w/ spectrum)
- unreactive
- non-toxic
- easy to remove from sample (low bp)
- gives single, intense resonance (∵12 x Hs)
6
Q
What is deuterium?
A
- D = ²₁H
- x NMR active isotope of H
7
Q
Common solvents for ¹H NMR
A
- CCl4- tetrachlromethane
- CDCl3- deuterotrichloromethane
- D2O- deuterium oxide
- C6D6
8
Q
Suggest why CDCl3 is a more effective solvent than CCl4 for polar molecules.
A
- CDCl3 - polar vs non-polar CCl4
- ~ IMF w/ polar molecules –> dissolce better
9
Q
A
