Carbon tunnelling, carbene reactions

In contrast to the above examples, dihydroxycarbene 63 does not undergo a tunneling rearrangement. 63 was made by the HVFP of oxalic acid 62 (Reaction 5.12), and its structure was confirmed by the comparison of the experimental and computed (CCSD(T)//cc-pVTZ) vibrational frequencies. 63 persists for days at 11 K, as does its dideutrated analog 2-63. The carbene is stabilized by it-donation from each oxygen lone pair into the empty p-orbital on carbon. This donation manifests in the very short C-0 distance of 1.325 A in 63, compared with the C-0... 

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