Day 2
Information in 1D 1 H NMR Observable Feature in Spectra Structural or purity characteristics 1. number of peaks 1. number of different types of protons 2. chemical shift (ppm) 2. chemical environment of proton 3. integration of peaks 3. ratio of different types of protons 4. splitting pattern 4. number of adjacent protons of (singlet, doublet etc.) different types 5. coupling constants 5. relative orientation of adjacent protons 6. peak shape (sharp or broad) 6. exchangeable protons 7. presence of other peaks 7. purity
4. Splitting Patterns number of peaks = n + 1 n = number of adjacent (equivalent) nuclei H H H H C C C NO 2 H H H 2.144 2.024 5 4 3 2 1 0 1 4 6 4 1 1 3 3 1 H H H H H H H H H quartet (q) quintet frequency frequency
Coupling (Splitting) Pascal’s triangle singlet 1 doublet 1 1 triplet 1 2 1 quartet 1 3 3 1
Splitting by two different types of adjacent protons doublet of doublet J 1 J 2 10 50 10 40 10 30 10 20 10 10
Splitting by two different types of adjacent protons
Splitting by two different types of adjacent protons X X X X Y X Y X Y X Y X
Information in 1D 1 H NMR Observable Feature in Spectra Structural or purity characteristics 1. number of peaks 1. number of different types of protons 2. chemical shift (ppm) 2. chemical environment of proton 3. integration of peaks 3. ratio of different types of protons 4. splitting pattern 4. number of adjacent protons of (singlet, doublet etc.) different types 5. coupling constants 5. relative orientation of adjacent protons 6. peak shape (sharp or broad) 6. exchangeable protons 7. presence of other peaks 7. purity
5. Coupling constants 1 - 3 Hz J 1,3 J vicinal J geminal J 1,2 7 - 9 Hz H H H H H H H J 1,4 0 Hz 12 - 15 Hz 7 Hz cis 8 Hz 10 Hz H ax H H H eq 0 - 2 Hz 5 Hz C C H eq H H N H ax 17 Hz trans axial to axial 8 - 10 Hz equat. to axial 2 - 3 Hz equat. to equat. 2 - 3 Hz
Karplus Equation (viscinal coupling) cinal coupling partners, coupling constant is measure of dihedral angle
Karplus Equation (geminal coupling) 10 - 12 Hz H H H 0 - 2 Hz H 12 Hz • coupling constant is measure of bond angle
Long-Range Coupling !ccurs through multiple bonds or 345 conformation. 4 J = 1.5 Hz H H CH ; 4 J = 2 Hz ! H H H H H ! H H Cl <r 4 J = 7.4 Hz H 4 J = 3 Hz
Coupling (Splitting) A Little Bit About J • Coupling constant J is same in both directions for a coupled pair. J ba = J ab same J H H H H a b a b ! (H a ) ! (H b ) • Coupled peaks are “tipped” toward each other 3.83 1.49 O Cl 0.90 3.65 3.37 4 2 0 4 3 2 1 0
Magnetic Inequivalence and Splitting Magnetic and chemical e.uivalence are different: Protons are chemically equivalent, so they don’t H b H b split one another. Molecule gives 2 H multiplets. H a H a But, the equivalent protons have different geometric relationships with other protons. So they are Cl Cl magnetically inequivalent, and split other protons differently. (Each signal is a dd .) a b a’ b’ H a H b Non-first order behavior
Putting it all together (Example 1) 7 Hz 7 Hz 7 Hz 18 Hz 18 Hz 12 Hz 12 Hz
Example 2 8 4 6 1 3 7 9 5 OH 10 2 1H 1H 1H 1H 2H 3H 2H 3H 1H 3H
Example 2 cont. 8 4 6 9a 1 3 7 H 5 1 OH 200 MHz H NMR spectrum of linalool, H 10 9b 2 5-6 ppm region. 5.071 5.077 5.239 5.245 Coupled to: Coupling constant (J): 5.151 Proton 5.017 5.159 5.830 5.023 8 9a 10.6 Hz 5.884 17.2 Hz 9b 5.917 5.970 5.115 5.109 10.6 Hz 9a 8 1.4 Hz 9b 5.101 9b 17.2 Hz 8 1.4 Hz 9a 4 1.4 Hz 5 (x2) 6.0 5.5 5.0 ppm 22.77 77.23 1 200 MHz H NMR spectrum of linalool, 5-6 ppm region.
Example 3
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