Extracting specific long range carbon - proton coupling constants is quite tedious. One way to simplify matters and obtain specific carbon - proton coupling constants is to apply the selective 2D heteronuclear J-resolved technique first introduced by Bax and Freeman in 1982 (JACS 104, 1099). This method employs a 13C spin echo with a selective 1H 180° pulse applied simultaneously with the 13C nonselective 180° pulse. A version of this sequence is shown in the figure below with a shaped adiabatic 13C 180° pulse.
In this sequence one obtains a 2D spectrum with 13C in the F2 domain and the long range couplings to the selectively inverted proton in the F1 domain. An example is shown in the figure below for toluene where the methyl protons were selectively inverted with a 20 msec Gaussian pulse.
All of the carbons coupled to the methyl protons are split into quartets in the F1 domain and the long range coupling constants which were very difficult to obtain from the coupled 13C spectrum can simply be read directly from the 2D spectrum.