NMR
Experiment times
NMR times is
always limited. The following should represent best practice for the
analysis of the majority of samples:
(a) Obtain proton spectrum.
(b) If the proton is clean and shows sufficient concentration then obtain COSY and/or HSQC.
(c) If the structure still cannot be confirmed then obtain 13C and/or HMBC spectra – Overnight.
(d) If the structure still cannot be confirmed consider specialist experiments (TOCSY, NOESY etc).
(An HSQC will provide the chemical shifts of C-H, CH2 and CH3 carbons with CH2 carbons shown with a different phase to CH and CH3) and this is usually a faster alternative to a DEPT).
Approximate times for default experiments on the Open Access instruments are shown below:
| |
Default Exp Time |
Scans (increments) |
Day / Night |
|
1H |
2 mins |
8 |
Day |
|
13C |
20 mins |
400 |
Night |
|
COSY |
5-7 mins |
1 scan (x256inc NUS50%) |
Day |
|
Fast HSQC |
5-7 mins |
2 scans (x256inc NUS50%) |
Day |
|
High Res HSQC |
15 mins |
2 scans (x512 NUS50%) |
Night |
|
HMBC |
25 mins |
4 scans (x512 NUS50%) |
Night |
|
DEPT |
20 mins |
400 |
Night |