NMR Spectroscopy: The n + 1 Rule and Spin-Spin Splitting

The n + 1 Rule

• Used to predict the number of peaks in an NMR spectrum for a given signal.
• Rule: If a proton has 'n' neighboring protons, expect 'n + 1' peaks.
• Applies only when the neighboring protons are chemically equivalent.

Example Analysis

• Red Proton:
  • Neighboring protons: 1
  • Peaks: 1 + 1 = 2
  • Result: Doublet
• Blue Proton:
  • Neighboring protons: 1
  • Peaks: 1 + 1 = 2
  • Result: Doublet
• Magenta Protons:
  • Neighboring protons: 0
  • Peaks: 0 + 1 = 1
  • Result: Singlet

Further Examples

Example 1

• Red Protons:
  • Neighboring protons: 1
  • Peaks: 1 + 1 = 2
  • Result: Doublet
• Blue Proton:
  • Neighboring protons: 2
  • Peaks: 2 + 1 = 3
  • Result: Triplet

Example 2: Bromoethanes

• Three Protons:
  • Neighboring protons: 2
  • Peaks: 2 + 1 = 3
  • Result: Triplet
• Two Protons:
  • Neighboring protons: 3
  • Peaks: 3 + 1 = 4
  • Result: Quartet

Example 3

• Red Protons:
  • Neighboring protons: 1
  • Peaks: 1 + 1 = 2
  • Result: Doublet
• Blue Proton:
  • Neighboring protons: 6
  • Peaks: 6 + 1 = 7
  • Result: Septet

Spin-Spin Splitting

• Occurs when protons are in different environments.
• No Splitting: Chemically equivalent protons do not show splitting.

Splitting Scenarios

• Adjacent Protons: Red and Blue protons split each other if in different environments.
• Separated by a Carbon: Typically no splitting occurs.
• Same Carbon: Can lead to splitting if protons are in different environments.

Key Takeaways

• Chemically equivalent protons don't show spin-spin splitting.
• Simple NMR spectra focus on adjacent protons for splitting.
• Protons on different carbons further apart generally do not cause splitting.