In contradiction of long-accepted mass spectrometric dogma, the site-specific y-hydrogen rearrangement is observed in alkylbenzenes in which both ortho positions are blocked with methyl substituents. Mass spectrometric studies of a series of five trimethyl-and three tetramethylisopentylbenzenes have shown that this rearrangement is only suppressed to a significant degree in those compounds in which all three positions ortho and para to the isopentyl group are blocked. Deuterium labelling has confirmed the y-site-specific origin of the migrating H atom while metastable studies have been used to investigate the mechanism of the rearrangement process.

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Ausgehend von der D‐Manno‐heptulose (Ia) wird entweder über die Stufen (Ib)‐(Id) oder über (IIa) und (IIb) das 7‐Phosphat (Ie) dargestellt.