One-Dimensional Experiments Utilizing J-Couplings

Homonuclear decoupling is presently not as popular as it used to be because of the relative ease with which we can now carry out 2-D experiments to obtain comparable information. 

Two important 1-D experiments that make use of J-couplings are the attached proton test (AIT) and the distortionless enhancement through polarization transfer (DEPT) experiment. Both the APT and DEPT experiments provide information about whefber or not the observed nucleus—virtually always —is protonated, and if so, 

imagine a mefbine signal fbat is on-resonance. Now split fbe mefbine C s into two populations Let be those mefbine C s 

Because only one resonance can be on-resonance, a slight modification to the pulse sequence is in order if we are to determine whether or not each is protonated. This modification allows the experiment to work for resonances that are off-resonance, and is accomplished with what is called a chemical shift refocusing pulse. If, after the first x, we simultaneously apply both a 180° and 180° pulse, we will (1) change the spin state of the H s boimd to the C s, and (2) flip the vectors so that after the x period they will refocus along either the +y- or —y-axis of the rotating frame. 

When we use the APT pulse sequence, methylene groups behave like the nonprotonated (Cup) groups, and methyl groups behave like the methine groups. 

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