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Chapter 15. Heteronuclear 2D Experiments

Chapter 15. Heteronuclear 2D Experiments. 15.0 Introduction 15.1 Heteronuclear correlation (HETCOR) and its variants (COLOC, HMBC etc) 15.2 Heteronuclear multiple-quantum coherence (HMQC) 15.3 Heteronuclear single-quantum coherence (HSQC). Introduction.

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Chapter 15. Heteronuclear 2D Experiments

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  1. Chapter 15. Heteronuclear 2D Experiments 15.0 Introduction 15.1 Heteronuclear correlation (HETCOR) and its variants (COLOC, HMBC etc) 15.2 Heteronuclear multiple-quantum coherence (HMQC) 15.3 Heteronuclear single-quantum coherence (HSQC)

  2. Introduction • The availability of other (“hetero”) nuclei than proton for multi-dimensional NMR spectroscopy is extremely useful, particularly, for macromolecules (of synthetic or biological origin) because the connectivity between protons and heteronuclear spins can be established in addition to the homonuclear multi-dimensional spectra. • Like homonuclear 2D spectroscopy, the central task in heteronulcear 2D experiments is to select proper coherence pathways so that the desired interaction can be elucidated. Heteronuclear 2D experiments can be more diverse because, e.g., the data acquisition can be carried out on heteronuclei (C-13, N-15 etc) or on protons (inverse detection).

  3. Heteronuclear correlation (HETCOR) and its variants

  4. During t1, the carbons that are coupled to protons are selected so that only those carbons are “visible” in the detection period. The choice of two fixed delays Δ1 and Δ2 is determined by smallest J-coupling we want to observe, i.e., when long- range coupled carbons (in addition to directly bonded carbons) are also to be observed: Δ1=1/2Jmin, Δ2=1/3Jmin.

  5. ωI ωS Enhanced Heteronuclear Correlation S(δI, δS)

  6. COrrelation via LOng-range Coupling(COLOC) The choice of two fixed delays Δ1 and Δ2 is determined by smallest J-coupling we want to observe, i.e., when long- range coupled carbons (in addition to directly bonded carbons) are also to be observed: Δ1=1/2Jmin, Δ2=1/3Jmin.

  7. Heteronuclear Multi-Bond Correlation (HMBC)

  8. Inverse Detection

  9. HSQC

  10. Points a-d (INEPT)

  11. Points e-g (Reversed INEPT)

  12. Phase Cycling

  13. HMQC

  14. Difference of HMQC and HSQC(I)

  15. Difference of HMQC and HSQC(II)

  16. 2D J Spectroscopy 2D methods that show coupling multiplets versus chemical shift. There is both a homonuclear and a heteronuclear version. Both methods are useful for resolving overlapping multiplets. They are also used to measure coupling constants. These sequences allow both J coupling and chemical shift evolution but re-focus the chemical shifts like a spin echo sequence (90 - - 180 -- acq).

  17. t1: J; t2: J+CS t1: JIS, t2: JIS+CSS

  18. Summary HETCOR, COLOC HMBC HSQC/HMQC J spectrosc. HSQC is now a “platform” for many more complicated pulse sequences.

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