Connectivities in molecules by INADEQUATE: recent developments

The INADEQUATE (Incredible Natural Abundance DoublE QUAntum Transfer Experiment) consists of a pulse sequence which eliminates the NMR signals from isolated spins (spin system A) displaying signals from coupled spins (spin system AX or higher spin systems). It is of great importance when applied to molecules with skeleton elements such as carbon, silicon or tungsten, all of which contain a small percentage of spin-1/2 isotopes embedded in magnetically inactive isotopes. Analysis of the AX type spectra gives one-bond and long-range coupling constants (see compound 6) and, most important, the connectivity pattern of the skeleton atoms in molecules of unknown structure such as the carbon compounds 1 or 2, the silicon compound 3 or the lithium compound 4b. Unfortunately, INADEQUATE is rather insensitive, in the case of carbon only one out of 104 molecules gives the desired response. Efforts to reduce this drawback are described; recently, a remarkable step forward has been made by concentrating the four lines of an AX spin system to just two signals (see Fig. 2). Copyright (C) 2001 John Wiley Sons, Ltd.