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Empirical Correlations

Empirical Correlations. for methylene of the type Y-CH 2 -X by adding D i to the chemical shift of methane ; d = 0.23 + D X + D Y. substituent constants Z i are added to the chemical shift of ethene ; d = 5.28 + Z gem + Z cis + Z trans.

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Empirical Correlations

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  1. Empirical Correlations for methylene of the type Y-CH2-X by adding Di to the chemical shift of methane; d = 0.23 + DX + DY

  2. substituent constants Zi are added to the chemical shift of ethene; d = 5.28 + Zgem + Zcis+ Ztrans

  3. substituent constants Si are added to the chemical shift of benzene; d = 7.27 + ∑Si

  4. First-Order Spin-Spin Coupling As closer the coupling nuclei as better they can interact and as higher is the coupling constant J. The number of bonds between two coupling nuclei is given as a prefix (e.g. a 3-bond coupling constant is given as 3J).

  5. -1/2 -1/2 +1/2 +1/2

  6. Each proton has a unique absorption (chemical shift d) but this absorption is altered by magnetic nuclei nearby. In 1H-NMR other protons but also any other magnetic nuclei such as deuterium, 13C, 19F, and 31P. First-order coupling is found for absorptions that satisfy Dn/J > 10 and any pair of chemically equivalent nuclei must also be magnetically equivalent.

  7. Pascal’s triangle

  8. C-H sees CH2 protons CH2 sees C-H proton (+1, 0, -1) (+1/2, -1/2)

  9. H-coupling in ethylbenzene Typical A2X3 ethyl pattern triplet quartet

  10. H-coupling and Integration (isopropylbenzene)

  11. 1H-NMR of Ethanol in CDCl3 Rapid exchange of OH: do not see coupling CH3CH2OH

  12. 1H-NMR of Ethanol in DMSO No exchange CH3CH2OH

  13. Doublet of Quartets CH3CH2OH Methylene group couples to OH and CH3;3J(CH2-OH) and3J(CH3-CH2)

  14. Benzyl Acetate Integration 5:2:3 At high resolution see multiplet

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