User:Benjah-bmm27/degree/2/CJA

NMR, CJA

edit

"Introduction to NMR Spectroscopy"

Overview

edit

Fundamentals

edit

Chemical shift

edit

NMR active nuclei

edit

Coupling

edit

Typical coupling constants

edit

One bond coupling

edit
  • e.g. 13C—1H in CHCl3:
  • 1JCH ≈ 120 Hz

Two bond (geminal) coupling

edit
  • e.g. bridgehead CH2 in norbornene:
  • 2JHH ≈ 10–18 Hz

Three bond (vicinal) coupling

edit
  • if rotation about C–C is free (e.g. e.g. H–C–C–H in ethyl iodide), 3JHH ≈ 8 Hz
  • if rotation is restricted, can predict 3JHH from dihedral angle φ with the Karplus equation: 3JHH = α cos2(φ)
  • 3JHH is maximal (i.e. 3JHH = α) where φ = 0° or 180°,

Benzene rings

edit
  • 3JHH, ortho ≈ 8 Hz
  • 4JHH, meta ≈ 2 Hz
  • 5JHH, para ≈ 0 Hz

Alkenes

edit
  • 3JHH, trans ≈ 16 Hz
  • 3JHH, cis ≈ 8 Hz
  • 2JHH, gem ≈ 5 Hz

Equivalence

edit

Fluxionality

edit

Technical details

edit

Beyond the scope of the course

edit