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Hello, why choloroform gives a negative triplet instead of a positive(just one hydrogen on the carbon) in DEPT 135. Can you give me an explanation |
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From what you have described, it sounds like you have run a DEPTQ experiment. Check the pulse sequence for your experiments (typical Bruker pulse sequences for DEPTQ are deptqsp, deptqgpsp, and deptqgpsp.2). Glenn Facey has done a comparison of DEPT-135 and DEPTQ experiments on his blog (http://u-of-o-nmr-facility.blogspot.com.au/2007/11/dept-and-deptq.html). Thanks, the link is really helpfull. - zikoooo (Jul 29 '14 at 01:20) |
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Is it deuterated chloroform? In that case it should give a 1:1:1 intensity triplet in 13C spectrum, and shouldn't give any signal in dept. There is probably a misadjustment of pulse length, or you didn't do a multiple of 32 scans for phase cycling in your dept expt. Actually, I found this signal 1;1;1 in all my spectra. I am using a Bruker 400Mhz. Which parameters should I change to get a "normal" positive signal for the chloroform which is a impurity in the deuterated solvent(chloroform). Cheers, - zikoooo (Jul 28 '14 at 06:16) I am doing 256 scans each. - zikoooo (Jul 28 '14 at 09:14) |
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Perhaps it is not chloroform. If you see a triplet with 1:2:1 intensities, that would suggest there is a CH2 group, which yields negative amplitude in DEPT 135. If the intensities are 1:1:1, that would be deutero-chloroform. Ideally it should not appear at all (no H, therefore no H-C transfer). If it does appear, it may be because the recycle delay is too short (first scan gives larger signal which defeats the phase cycling). Try a longer recycle delay, or use some dummy scans, and it should disappear. Note added soon after posting: I see that Anne Baudouin responded similarly while I was typing. Actually, I found this signal 1;1;1 in all my spectra. I am using a Bruker 400Mhz. Which parameters should I change to get a "normal" positive signal for the chloroform which is a impurity in the deuterated solvent(chloroform). Cheers, - zikoooo (Jul 28 '14 at 06:16) |
Actually, I found this signal 1;1;1 in all my spectra. I am using a Bruker 400Mhz. Which parameters should I change to get a "normal" positive signal for the chloroform which is a impurity in the deuterated solvent(chloroform). Cheers, - zikoooo (Jul 28 '14 at 01:48)