The mass spectrum of n-octane shows a prominent molecular ion peak (m>z 114). There is also a large peak at m>z 57,but it is not the base peak. The mass spectrum of 3,4-dimethylhexane shows a smaller molecular ion, and the peak atmass 57 is the base peak. Explain these trends in abundance of the molecular ions and the ions at mass 57, and predict theintensities of the peaks at masses 57 and 114 in the spectrum of 2,2,3,3-tetramethylbutane.

SPECTROSCOPY 4. a) Symmetry: Provide the number of expected signals (ignore splittings) in the 'H and 13C NMR spectra of the following compounds: 1H NMR: 13C NMR: 1H NMR: 13C NMR: N

Analysis of a sweet-smelling, neutral compound of carbon, hydrogen and oxygen produced the following results: %C = 54.5; %H = 9.1. From its mass spectrum, the molecular ion had a mass/charge ratio of 88. Its infra-red spectrum showed a prominent peak at 1735 cm–1. Figure below shows the NMR spectrum of the compound. Suggest a structural Formula for this compound.

8. Sketch the off-resonance-decoupled 1³C spectra of the following compound. H H C C-H H The splitting pattern of off-resonance decoupled spectrum indicates the number of protons attached to the carbon. 13C nuclei are split only by the protons attached directly to them. The N + 1 rule applies: a carbon with N number of protons gives a signal with N + 1 peaks (e.g. carbon atom with one proton appears as a doublet; carbon with two attached protons gives a triplet etc.) • Carbon atoms with more hydrogens absorb more strongly.