Standard NMR Experiments
Detailed information on frequencies, standard und referencing is available from the IUPAC recommendations (2008).
Frequencies (BF) [MHz]
|Nucleus||AVANCE 400||AVANCE 600||Reference|
For all 13C-Experiments the concentration should be as high as possible.
In order to avoid useless 13C experiments the quality of the samples is verified by the signal-to-noise ratio of the 1H spectrum. If certain conditions are not fulfilled the 13C experiment is automatically cancelled on weekdays. Samples with low concentrations should be planned for the weekend.
Reference: 13C spectra are automatically referenced to the 13C shift of the deuterated solvent as long as the signal pattern is not disturbed too much.
|13C Chemical Shifts of Deuterated Solvents|
|Solvent||δ [ppm]||Solvent||δ [ppm]||Solvent||δ [ppm]||Solvent||δ [ppm]|
A comprehensive list of 1H and 13C chemical shifts of numerous impurities (c.f. H2O) in the common solvents is available in Organometallics 2010, 29, 2176–2179.
Standard experiments usually consist of combined series of interdependent spectra, for example
1H (PROTON) - 13C (C13CPD) - 13C (C13DEPT135p)
The proton spectrum determines the number of scans (NS) of the 13C spectrum (256, 1024 or abortion). The phase of the DEPT spectrum as well as the referencing (SR) is transferred from the preceding 13C spectrum.
Optimization of the Spectral Width SW
In case of 1D spectra, e.g. 19F or 31P spectra, a special option may be selected: A survey spectrum is recorde with reduced number of scans. Depending on the quality of the spectrum (signal-to noise ratio) the measurement is either
(b) redorded with the unchanged sweep width with a scan number increased by a factor of 4 or
(c) the spectral width (SW) is optimiized and the scan number NS is retained or decreased by a factor of 4, depending on the quality of the survey spectrum.
The additional experiments are saved with the following experiment numbers (expno):
For 19F spectra (AVANCE 400 only), there is a special sequence consisting of
(a) 19F survey spectrum,
(b) Sweep optimized 19F detail spectrum,
(c) 1H decoupled 19F spectrum with the parameters taken from (b),
(d) 19F decoupled 1H spectrum with the decoupler set to the center frequency (O1) from (b)
(e) regular 1H spectrum.