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At low temperature the four terminal methyl groups contain 12 equivalent protons and the two bridging methyls contain six, giving the $2:1$ pair of singlets. On warming, terminal and bridging positions interchange rapidly on the NMR timescale. A methyl group then samples both environments during the observation, producing a single population-weighted resonance, ${\delta }_{\mathrm{av}}=(2{\delta }_{\mathrm{term}}+{\delta }_{\mathrm{bridge}})/3$. This Chemical exchange in NMR is not merely faster rotation of each methyl about its own Al–C direction, which cannot turn a terminal site into a bridge.

The concentration independence argues against a rate-limiting collision between two intact dimers. An intramolecular bridge-opening and reclosing rearrangement can exchange which methyls are bridges; a unimolecular dissociation followed by rapid reassociation is another mechanism whose observed rate could be concentration independent. The spectra establish rapid site exchange, but not a unique elementary exchange pathway. A variable-temperature line-shape analysis or exchange experiment would be needed to distinguish detailed mechanisms. Primary organoaluminium studies describe the same low-temperature resolution and warm-temperature averaging, while considering dimer dissociation.^[ref]