1. Introduction to NMR Spectroscopy and Imaging Lecture 07 Basic Heteronuclear 2D Experiments (Spring Term, 2011) Department of Chemistry National Sun Yat-sen University 核磁共振光譜與影像導論

2. Basic Heteronuclear 2D Experiments Introduction Heteronuclear correlation (HETCOR) and its variants (COLOC, HMBC etc) Heteronuclear multiple-quantum coherence (HMQC) Heteronuclear single-quantum coherence (HSQC)

3. 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).

6. Heteronuclear correlation (HETCOR) and its variants

7. 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=1/2J min, Δ2=1/3J min.

8. Enhanced Heteronuclear Correlation S(δ I, δ S ) ωIωI ωSωS

11. 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=1/2J min, Δ2=1/3J min.

13. Heteronuclear Multi-Bond Correlation (HMBC)

18. Inverse Detection

19. HSQC

21. Points a-d (INEPT)

22. Points e-g (Reversed INEPT)

23. Phase Cycling

28. HMQC

36. Difference of HMQC and HSQC(I)

37. Difference of HMQC and HSQC(II)

38. 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).

39. t1: J; t2: J+CS t1: J IS, t2: J IS +CS S

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