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J. Corey, who was at that time an assistant professor at Illinois and later became a colleague at Harvard, was one of the people with whom I had dinner on a fairly regular basis at the Tea Garden, a passable restaurant in Champaign-Urbana. We often discussed recent work that we thought might be of mutual interest and one day I described the studies that I had made of vicinal coupling constants. Corey immediately recognized the possibility of using the results for structure determination and shortly published what is probably the ¿rst application in organic chemistry.

In the evolution period e one t1 section follows with a 180° pulse on the protons in the middle of t1. During t1 the term − 2 I H z I Cy develops 13C chemical shift as described by Equation (1). The 180° proton pulse p5 eliminates the J(C,H) couplings in F1 and for simplicity is not shown in the equations. (1) ȍ t1IC z − 2 I H z I C y ⎯⎯C⎯ ⎯→ − 2 I H z I C y cosȍCt1 + 2 I H z I C x sinȍ Ct1 After the chemical shift evolution an editing period in the mixing period m serves for different signs of CH and CH3 or CH2 signals.

Today, mostly a gradient-selected variant is used, with the gradients operating in the echo-antiecho method for sensitivity reasons. Additional sensitivity improvement by a factor of 2 is achieved by a double back INEPT transfer; however, this occurs only for CH groups [2-5]. In reference [6], applications for long-range spin couplings are discussed. In most cases it is desirable to obtain an editing of 2D H,X correlation spectra. This can yield a multiplicity determination in case of overlapping 13C signals, or reveal CH moieties in the presence of many CH2 groups or NH2 groups in the middle of many NH groups in proteins.

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