1. Lecture 3 NMR Spectroscopy: Spin-spin Splitting in 1 H NMR Integration Coupling Constants 13 C NMR Sample Preparation for NMR Analysis Due: Lecture Problem 1

2. 1 H NMR Spectrum of Ethanol: Spin-Spin Splitting ppm (  ) CH 3 CH 2 O H TMS a - triplet b - quartet c - singlet a a b b c c downfield upfield

3. Spin-Spin Splitting CH 3 CH 2 O H a - triplet b - quartet c - singlet a b c General rules: Neighboring, non-equivalent protons split each other’s signals Equivalent protons do not split each other’s signals Use the n + 1 rule to predict the splitting pattern of a proton’s signal n + 1 rule The signal of a proton with n equivalent neighboring protons is split into a multiplet of n + 1 peaks. In ethanol, a neighbors b; they split each other’s peaks. Note that b neighbors c and no splitting occurs between the two; b is only affected by a. In general, protons that reside on heteroatoms (O, N) do not get involved with spin-spin splitting with neighboring protons. Thus, c appears as a singlet.

4. Spin-spin Splitting

5. Spin-Spin Splitting Determine the splitting patterns for the signals in the 1 H NMR spectra of the following compounds.

6. Complex Spin-Spin Splitting Consider the 1 H NMR spectrum of a substituted alkene:

7. Spin-Spin Splitting

8. Determine the splitting patterns for the signals in the 1 H NMR spectra of the following compounds.

9. 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 1. Measure the length of the integral with a ruler 2. Establish a relative ratio of protons (divide each length by the lowest number)

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

11. 1 H NMR Spectrum of a Taxol Derivative Taken from Erkan Baloglu’s Masters Thesis

12. Nuclear Magnetic Resonance Information Gained: Different chemical environments of nuclei being analyzed ( 1 H nuclei): chemical shift The number of different types of H’s: number of signals in spectrum The numbers of protons with the same chemical environment: integration The number of protons are bonded to the same carbon: integration The number of protons that are adjacent to one another: splitting patterns The exact protons that are adjacent to one another: coupling constants

13. 13 C NMR Spectroscopy Information Gained: Different chemical environments of carbons in molecule: chemical shift The number different types of C’s: number of signals in spectrum Differences from 1 H NMR: No splitting of signals (proton-decoupled); thus, only singlets No integration ppm scale ranges from 0 to 220 ppm

14. 13 C NMR Chemical Shifts Like with 1 H NMR, the more shielded the carbon nuclei, the more upfield its signal will appear and vice versa. downfieldupfield

15. 13 C NMR Spectrum of Chlorohexane

18. 13 C NMR Correlation Chart

19. NMR Sample Preparation & CDCl 3 Sample Prep: Dissolve ~32 mg of sample in CDCl 3 in an NMR tube. Why use CDCl 3 ? Deuterated solvents are necessary in NMR because deuterium is NOT NMR active and will not interfere with your sample’s spectrum. CDCl 3 is 98-99% pure with a trace amount of CHCl 3. You will see a small solvent peak at ~7.26 ppm due to CHCl 3 ( 1 H NMR); see a triplet at 77 ppm 13 C NMR. This peak serves as a reference peak; DO NOT count it as one of your sample’s signals!