User:Benjah-bmm27/degree/2/CJA
Appearance
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