Exchange experiments/spectroscopy excitation

Figure 1.45 Coherence transfer pathways in 2D NMR experiments. (A) Pathways in homonuclear 2D correlation spectroscopy. The first 90° pulse excites singlequantum coherence of order p= . The second mixing pulse of angle /3 converts the coherence into detectable magnetization (p= —1). (Bra) Coherence transfer pathways in NOESY/2D exchange spectroscopy (B b) relayed COSY (B c) doublequantum spectroscopy (B d) 2D COSY with double-quantum filter (t = 0). The pathways shown in (B a,b, and d) involve a fixed mixing interval (t ). (Reprinted from G. Bodenhausen et al, J. Magn. Resonance, 58, 370, copyright 1984, Rights and Permission Department, Academic Press Inc., 6277 Sea Harbor Drive, Orlando, Florida 32887.)...

The study by Crutchley et al. demonstrates that a relatively unsophisticated level of theory in conjunction with spectroscopy may be all that is necessary to predict trends in antiferromagnetic exchange derived from frontier orbitals. However, for a quantitative understanding, it is also clear from Section 2.45.2 that ab initio Cl calculations, involving all the single and double excitations of the valence electrons, are required to get reasonable agreement with experiment. 

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