11B Double Quantum - Single Quantum Correlation Spectroscopy

The 2D ¹³C INADEQUATE method provides double quantum - single quantum (DQ/SQ) correlations and enables one to determine the carbon - carbon skeleton of small organic molecules.  The method is quite insensitive for ¹³C since the natural abundance of ¹³C is only 1.1% and the chance of having two adjacent ¹³C nuclei is only 1 in 8264.  For spins other than ¹³C, for which the natural abundance is high, one expects the sensitivity of DQ/SQ correlation spectroscopy to be much higher.  ¹¹B has a natural abundance of 80.42% and the chance of having two adjacent ¹¹B nuclei in compounds with boron-boron bonds is 1 in 1.55.  ¹¹B NMR spectra are often sufficiently broad due to efficient quadrupolar relaxation such that homonuclear ¹¹B - ¹¹B J coupling is unresolved however the T₂'s are long enough to allow the collection of  2D ¹¹ B COSY and 2D DQ/SQ data.  The figure below shows the 2D ¹¹B DQ/SQ correlation spectrum of ortho-carborane.  The ¹¹B bonding connectivity can be determined easily from the spectrum.