0
|
Hello, could you tell me which HSQC and E-HSQC program are recommendable ? These are Bruker HSQC pulse programs: hsqcph, hsqcphpr, hsqcphps, hsqcgpph. hsqcgpph2. hsqcetgp. hsqcetgpsp. hsqcetgpsp.2. hsqcetgpsp.3, hsqcetgpsi. hsqcetgpsi2. hsqcetgpsisp. hsqcetgpsisp2. hsqcetgpsisp.2. hsqcetgpsisp2.2, hsqcdhetgpsp, and so on. There are Bruker E-HSQC pulse programs: hsqcedgpph, hsqcedetgp, hsqcedetgpsp, hsqcedetgpsp.3, hsqcedetgpsisp, hsqcedetgpsisp.2, hsqcedetgpsisp2, hsqcedetgpsisp2.2, hsqcedetgpsisp2.3, and so on. I have a few mg of my sample to be determined but it probably has one insensitve carbon on 1D-13C experiments. I would like to find and assign this carbon with HSQC or E-HSQC. Thanks. |
|
1
|
The basic scheme of the HSQC involves the transfer of magnetization via the 1JCH-bond. Mostly, the value for this heteronuclear coupling is set to an average 1JCH of 145 Hz. However, the size of 1JCH is correlated closely with the hybridization of the C-H bonding orbital so 145 works fine for sp3 and sp2. The value of 145 Hz for 1JCH my be not correct for sp hybridization (ca. 250 Hz) or increased size of the coupling for electronegative substituents (or decreased for electropositive substituents). Many examples can be found in references whioch might explain why some correlations may seem insensitive! |
|
0
|
Two good answers already - the answer is that it depends on your particular molecule and situation. My favourite for general use is the sensitivity improved, edited, gradient experiment with adiabatic pulses. In Bruker terms, "hsqcedetgpsisp2.2" or the 2.3 version. As for the "insensitive carbon" - why is it insensitive? Is it broad? HSQC is pretty sensitive so I am surprised if you don't see a signal... |
|
0
|
Hey, I don't know what do you mean by "insensitive carbon". It's relaxing too fast or too slow ? Maybe some kind of quadrupolar neighbour ? Please tell me something more about it. I'm using "hsqcedetgp" for typical measurments. |
|
0
|
Hello, the answer is quite difficult. Akadiusz is right, ... what do you want to "see"/detect? This is also the main reason to get no ONE HSQC, instead you get a bunch of HSQC's ... Do you have a z-gradient in your probe? HSQC uses phase cycling and this takes time, and is very sensitive also. If you switch to the gHSQC branch, there you can you use PulseFieldGradients to select your correct signals, ... less artefacts but also slightly less sensitive than the other one. gHSQC with "AD" there are adabatic shaped pulses used, ... broader decoupling window for carbons, but slightly less than, ... BRUKER has it's own slang in nameing these different versions of HSQC. What do you want to detect and separate in your spectra? This is the main question. Ulrich Haunz |
|
0
|
In addition, I do prefer the hsqcedetgp for compounds containing CH, CH2 and CH3's, e.g. steroids. With CH and CH3 having the same phase and CH2 of opposite phase, one can easily distinguish geminal protons from others. For most compounds, the hsqcetgp works really fine. |
