A high-resolution (13)C 3D CSA-CSA-CSA correlation experiment by means of magic angle turning

It is shown in this paper that a previously reported 90 degrees sample flipping (13)C 2D CSA-CSA correlation experiment may be carried out alternatively by employing constant slow sample rotation about the magic angle axis and by synchronizing the read pulse to 13 of the rotor cycle. A high-resolution 3D CSA-CSA-CSA correlation experiment based on the magic angle turning technique is reported in which the conventional 90 degrees 2D CSA-CSA powder pattern for each carbon in a system containing a number of inequivalent carbons may be separated according to the isotropic chemical shift value. The technique is demonstrated on 1,2,3-trimethoxybenzene in which all of the overlapping powder patterns that cannot be segregated by the 2D CSA-CSA experiment are resolved successfully by the 3D CSA-CSA-CSA experiment, including even the two methoxy groups (M(1) and M(3)) whose isotropic shifts, confirmed by high-speed MAS, are separated by only 1 ppm. A difference of 4 ppm in the principal value component (delta(33)) between M(1) and M(3) is readily obtained.