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Friday, November 16, 2007

DEPT and DEPTQ

Many of you run both standard 13C and 13C DEPT-135 spectra of your compounds. This may take a considerable period of time (and cost a considerable amount of money) if your sample is dilute. You can run a single DEPTQ-135 spectrum of your compound and get the same amount of information. This may save a great deal of spectrometer time. A DEPTQ-135 spectrum is the same as a DEPT-135 spectrum except the quaternary carbons are present and 180 degrees out of phase with respect to the CH and CH3 carbons. Note also that the commonly used deuterated solvents will show up in a DEPTQ spectrum and can be used for chemical shift referencing. Below is the standard 13C spectrum, the DEPT-135 spectrum and the DEPTQ-135 spectrum of ethylbenzene.

2 comments:

Steven said...

I was told DEPTQ-135 less sensitivity than routine carbon. Is this true. My understanding, DEPTQ-135 should almost the same sensitive as DEPT-135, which almost 4 times more sensitive than routine carbon. Is this true?

Glenn Facey said...

Dear Steven,

Thank you for your question. The answer is not as simple as you may think. The sensitivity of the DEPTQ vs the DEPT or 13C with 1H decoupling depens on the multiplicipy of the carbon and the recycle delay however the dependaence is not the same for each experiment. The protonated carbons are significantly enhanced in both a DEPT and DEPTQ experiment relative to a standard 13C spectrum with proton decoupling due to magnetization transfer from protons. The sensitivity per unit data collection time is also increased in both the DEPT and DEPTQ as the repetition rate depends on the T1 for the protons rather than the T1 for the carbons. It is true however that the sensitivity for quaternary carbons is greater in a standard 13C spectrum with proton decoupling. For more information see the following reference:

R. Burger and P. Bigler, J. Mag. Res. 135, 529 (1998).