For proton NMR spectra, does a peak at 0 ppm indicate anything significant or is it likely to be a signal arising from a solvent?
A peak at 0 ppm in proton NMR spectra is usually an indication of the solvent used rather than a signal from the compound being analyzed. This peak arises due to the reference compound used in NMR experiments, typically tetramethylsilane (TMS), which is assigned the chemical shift of 0 ppm. TMS is used as a reference because it has a predictable and stable chemical shift.
To obtain this reference, a small amount of TMS is added to the sample being analyzed. The TMS molecules, having a different chemical environment than the sample molecules, produce a distinct peak at 0 ppm. This peak is used to calibrate the chemical shift scale of the spectrum, allowing for accurate assignment of other peaks in the spectrum.
So, if you observe a peak at 0 ppm in a proton NMR spectrum, it is typically just an artifact of the solvent and the reference compound, and not an indication of any significant signal from the compound of interest. The main focus should be on the peaks that are observed at different chemical shifts, as these provide valuable information about the structure and chemical environment of the molecule being analyzed.