Deprotonation at the unique C-H of the cation shown with a strong base gives a neutral species. Which description of this species is correct?

AA singlet carbene, stabilised by donation of the lone pairs of both nitrogens into the empty p orbital.
BA triplet carbene with two unpaired electrons.
CA carbocation with a vacant p orbital and a positive charge.
DA carbanion with eight electrons on carbon and no empty orbital.

Answer: A

The cation shown is a tetramethylformamidinium ion; removal of H

^{+}

from its CH carbon leaves a neutral carbon with a lone pair in the sp

^{2}

orbital and a vacant p orbital, that is a carbene. Both neighbouring nitrogen atoms donate lone pairs into the vacant p orbital, which makes this singlet diaminocarbene a stable carbene. The product is neutral, so it is neither a carbanion nor a carbocation.

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Deprotonation at the unique C-H of the cation shown with a strong base gives a neutral species. Which description of this species is correct?

Answer: A

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