NMR Spectroscopy (Organic) (complete)

Question 1

When does nuclear spin occur and what can it produce in NMR Spectroscopy?

Answer 1

• Occurs when the number of protons and neutrons in an element don’t match.
• Can produce/generate a small magnetic field.

Question 2

What are the conditions for the solvents used during H NMR?

Answer 2

liquid at room temp, non-polar (some exceptions), no nuclear spin.

Question 3

What is used to calibrate a H NMR spectrum and why?

Answer 3

• Tetramethylsilane (TMS)
• Only gives one signal
• Non-toxic
• Inert
• Low boiling point so can be easily removed from sample afterwards
• give a signal that is further right than most of the signals from organic compounds.

Question 4

What are the spectra recorded on in H NMR?

Answer 4

• Chemical shift - how far the signal is away from the signal for TMS (ppm)

Question 5

Give the equation from chemical shift.

Answer 5

( (Field for TMS - Field measured) / Field for TMS ) x 10^6

Question 6

What do the vertical and horizontal scale/axis mean on a chemical shift spectrum?
(H NMR)

Answer 6

vertical = intensity of absorption
horizontal = how far each signal is shifter away from that for TMS

Question 7

Give the calculation for working out the number of lines for the splitting pattern on a H NMR spectrum

Answer 7

no lines = 1 + number of inequivalent H atoms on adjacent C atoms.

Question 8

Give the similarities and differences between H NMR and C NMR

Answer 8

Both - have one signal for each set of equivalent H or C atoms, and the closer the atom to a very electronegative atom and/or double bond, the grater the chemical shift.
H NMR - relative area of signals related to relative number go H atoms, and the signal can be split by H atoms on adjacent atom.
C NMR - no link between area of signals related to number of C atoms, and no splitting (all singlets)