Outline why the signal at 1.0 ppm is a triplet.

Suggest why it is necessary to include an internal reference standard in a sample when its \(^{\text{1}}{\text{H}}\) NMR spectrum is being determined and why tetramethylsilane (TMS) is used for this purpose.

next to a carbon atom bonded to two H atoms/protons / OWTTE;

changes in absorption frequency (very) small / magnetic field can vary (slightly);

Accept “providing a point from which to measure the shift” / OWTTE.

only single signal / well removed from other signals / very strong absorption / chemically inert / non-toxic / easily removed from sample;

Many students recognized that the simplicity of the NMR spectrum determined which structural isomer the compound was. Sometimes students managed to identify the structure, but were unable to explain the way in which the NMR spectrum supported this. The splitting patterns were not clear as they were not necessary for identifying the compound, though one was given in part (b), with the reason it was a triplet being quite well answered. Few were aware of the problems of fluctuating fields that can require the inclusion of an internal standard, something that is unnecessary in other forms of spectroscopy, but almost all students knew an advantage of using TMS as this standard.

Many students recognized that the simplicity of the NMR spectrum determined which structural isomer the compound was. Sometimes students managed to identify the structure, but were unable to explain the way in which the NMR spectrum supported this. The splitting patterns were not clear as they were not necessary for identifying the compound, though one was given in part (b), with the reason it was a triplet being quite well answered. Few were aware of the problems of fluctuating fields that can require the inclusion of an internal standard, something that is unnecessary in other forms of spectroscopy, but almost all students knew an advantage of using TMS as this standard.