Lecture 9

1. Lecture 9 NMR: Splitting Patterns/Coupling, Integration, Coupling Constants This week in lab: • Ch 6: Procedure 1 & PreLab Due; Quiz 3 • Due: Chapter 4 Final Report. Please do question #9 INSTEAD OF question #8!! Next week in lab: • Ch 6: Procedure 2 • Due: Chapter 5 Final Report

2. Spin-Spin Splitting (Coupling) • General rules: • Neighboring, non-equivalent protons split each other’s signals. Nuclei • “communicate” via bonding electrons. • Neighboring Equivalent protons do not split each other’s signals • Use the n + 1 rule to predict the splitting pattern of a proton’s signal • Protons that reside on heteroatoms (O, N) do not get involved • with spin-spin splitting with neighboring protons. n + 1 rule The signal of a proton with n neighboring protons (equivalent to each other*) is split into a multiplet of n + 1 peaks. *Note: It’ll appear that there are exceptions to this!

3. Spin-Spin Splitting (Coupling) Determine the splitting patterns for the signals in the 1H NMR spectra of the following compounds. First need to know about equivalency!

4. Spin-Spin Splitting (Coupling) Determine the splitting patterns for the signals in the 1H NMR spectra of the following compounds. First need to know about equivalency! n + 1 rule The signal of a proton with n neighboring protons (equivalent to each other*) is split into a multiplet of n + 1 peaks. *Note: It’ll appear that there are exceptions to this; see examples above!

5. Aromatics: Long-Range Coupling H’s on aromatic rings may couple with non-neighboring protons due to long-range coupling. You will see this in lab! Why? Nuclei “communicate” via bonding electrons - p electrons that are in resonance will allow non-neighboring H’s to “communicate” and couple/split. This leads to complex splitting.

6. Splitting Summary # of neighboring H’sMultiplet of Signal 0 Singlet (s) 1 Doublet (d) 2 Triplet (t) 3 Quartet (q) 4 Pentet (Quintet or Multiplet) (p, m) 5 Sextet (Multiplet) (m) 6 Septet (Multiplet) (m)

7. Nuclear Magnetic Resonance Use: To assist in the elucidation of a molecule’s structure Information Gained: • Different chemical environments of nuclei being analyzed (1H nuclei): chemical shift • The number of nuclei with different chemical environments: number of signals in spectrum • The numbers of protons with the same chemical environment: integration • Determine how many protons are bonded to the same carbon: integration • Determine the number of protons that are adjacent to one another: splitting patterns • Determine which protons are adjacent to one another:coupling constants

8. Integration • Area underneath signal; NMR machine will give integrals • First, gives the relative ratio of different types of protons in compound • Second, allows determination of actual ratio of different types of protons Measure the length of the integral with a ruler Establish a relative ratio of protons (divide each length by the lowest number)

9. Coupling Constants (J) Protons that split each other’s peaks will have the same coupling constant or J value.