I've just been using a pulse sequence for long-range C-H correlation (HMBC)
described in '100 and More Basic NMR Experiments'. This was experiment 10.13,
which has a low-pass filter, a BIRD sandwich, and is phase-sensitive using
TPPI. (All the bells and whistles!)
The result is very clean, with almost no 1JCH breakthrough, but it has a
puzzling feature: the only reasonable phase correction has some of the peaks up
and some of the peaks down. What _does_ this mean? Unfortunately the compound
is an unknown so I don't know what the answer should be.
Is the phase difference giving me more information? Is it an artefact which
depends on how the refocussing cycle matches the coupling constants? If so,
should some peaks be missing? Is it something else entirely? Any suggestions
would be welcome.
The experiment was done using Bruker's sequence invblrndtp.mo, with the long-
range nJCH set to 5Hz, on a DPX400 without gradients.
Alan
----------------------------------------------------
Dr A S F Boyd Chemistry Department
NMR Spectroscopist Heriot-Watt University
phone: +44-131-451 3214 Riccarton
fax: +44-131-451 3180 Edinburgh
a.s.f.boyd@hw.ac.uk EH14 4AS
http://dava.che.hw.ac.uk/ Scotland
----------------------------------------------------