C JMOD APT Experiment

The J-MODulated (JMOD) C experiment, also known as Attached Proton Test (APT) was the first and simplest way to determine C multiplicities. In contrast to DEPT no polarization transfer is included in the pulse sequence (Fig. 3.16) and as a consequence the signals of quaternary carbons are visible in the spectrum, but the sequence is far less sensitive than DEPT or INEPT. The value of D2 is used to differentiate between the different carbon multiplicities. The signal intensities of quaternary carbons are not influenced by the value of D2 for D2 equal to 1 CH and CH, groups have maximum negative intensity and CHj has maximum positive intensity. For D2 equal to 1 /C2 J, ) only the signals of quaternary carbons are visible. 

JMOD (APT) is usually performed with broadband H decoupling and is relatively sensitive to the precise matching of the delay D2 to the J,., coupling constant, and so is less easier to use than the polarization techniques DEPT and INEPT. On the other hand, only one single experiment is necessary to measure the signals of all carbon multiplicities. 

The experiment is used for solving simple structural problems, for the evaluation of chemical shifts and the determination of the multiplicities of individual carbon signals (including quaternary centres). 

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