tag:blogger.com,1999:blog-3300702123878659843.post4590312418493319060..comments2024-03-26T05:25:50.831-04:00Comments on University of Ottawa NMR Facility Blog: Weak One-bond or Multiple Bond Correlations in 1H / 13C HMQC / HSQC SpectraGlenn Faceyhttp://www.blogger.com/profile/05146575170575279335noreply@blogger.comBlogger4125tag:blogger.com,1999:blog-3300702123878659843.post-15287618126592577952012-04-19T15:06:17.411-04:002012-04-19T15:06:17.411-04:00Dear Ray,
The reason behind the observations you ...Dear Ray,<br /><br />The reason behind the observations you make in your HMQC spectrum is that there is a delay in the HMQC sequence which is set based on the reciprocal of an "average" one-bond carbon-proton coupling constant. Your sample gives very weak correlations for the terminal alkynes because the one-bond carbon-proton coupling constants are much different than the average and the delay in the pulse sequence is not appropriate for your sample. Adjusting the delay in the HMQC will give you much stronger signals.<br /><br />I have aslso made similar observations in DEPT spectra (see: http://u-of-o-nmr-facility.blogspot.ca/2007/11/why-does-my-quaternary-alkyne-carbon.html ). The explanation is much the same. There is a delay in the sequence based on the reciprocal of the "average" one bond coupling constant.<br /><br />GlennGlenn Faceyhttps://www.blogger.com/profile/05146575170575279335noreply@blogger.comtag:blogger.com,1999:blog-3300702123878659843.post-49618788785618715712012-04-18T16:38:49.350-04:002012-04-18T16:38:49.350-04:00Hi Glenn,
I was searching for some info about thi...Hi Glenn,<br /><br />I was searching for some info about this and found your blog. This particular case happened to me as well. I just measured the HMQC of my compound which has two terminal alkyne groups. I noticed the unusually weak one-bond correlation between the terminal proton and the terminal carbon, also the two-bond correlation of the proton with the other alkyne carbon. Do you know or do you have any paper or any theory that can explain why this happens?<br /><br />Also, I measured the DEPT 90 and 135 for this compound, interestingly both alkyne carbons (terminal and the other) shows up in DEPT 90. In DEPT 135, both carbons also shows up in the positive signal region (CH). And the peaks for both carbons in both spectra are quite strong! Again, do you have any paper or theory as why this can happen?<br /><br />Cheers,<br />Ray<br />PhD studentray_ap88https://www.blogger.com/profile/10401052277788668123noreply@blogger.comtag:blogger.com,1999:blog-3300702123878659843.post-22658637490160880902009-10-27T08:27:13.244-04:002009-10-27T08:27:13.244-04:00Elizabeth,
Most Bruker HMQC or HSQC pulse program...Elizabeth,<br /><br />Most Bruker HMQC or HSQC pulse programs calculate the delay, d2 in the program based on a constant, CNST2, where CNST2 is typically set to a value of 145 (the average 1 bond proton carbon coupling constant). If you wanted to optimize your HMQC or HSQC sequence of 250 Hz coupling, simply type "CNST2 250" before you start collecting data.<br /><br />GlennGlenn Faceyhttps://www.blogger.com/profile/05146575170575279335noreply@blogger.comtag:blogger.com,1999:blog-3300702123878659843.post-62423356673175880392009-10-26T16:28:02.246-04:002009-10-26T16:28:02.246-04:00Hello Glen F.
My name is Elizabeth and I have a...Hello Glen F. <br /><br />My name is Elizabeth and I have a little problem, I work whit a Bruker Avance 300 MHz but, change J it isn´t easy for me, How may I do it?, How may change the delays for change J=145 Hz, J=250 etc.<br /><br />I am beginning, could you helpme?<br /><br />thanks..Unknownhttps://www.blogger.com/profile/04217988224108954306noreply@blogger.com