Correct way to draw a carbene What is the correct way to draw a carbene? On most/all material I have seen, both singlet and triplet carbenes are depicted as so:



With 2 "dots" representing the non-bonding electrons on either a singlet or a triplet carbene.

However in a class today my tutor was adamant that a singlet carbene should be drawn with a positive and a negative sign on the carbon. His argument as such was that "you have an empty and a full orbital and so the empty orbital corresponds to the positive sign, the full orbital corresponds to the negative sign".

So my question is - How is a carbene correctly drawn? As above or with a carbon bearing both a positive and a negative sign?
Put simply, there's no precedent for this unusual depiction of a singlet carbene.

Your comment about most carbene depictions, for both singlet and triplet carbenes is true, but a bit lazy. Yes, many chemists, frequently just draw two electrons as a lone pair on the carbon for both. In principle, with a moment's thought, you can often deduce the likely spin state.

As described, by the comment above, the standard for 2D chemical structure depiction is the IUPAC guide Graphical representation standards for chemical structure diagrams



In short, there's a difference in representing a triplet (two unpaired electrons), which should show preferably two separate electron "dots."

For a singlet, the lone pair is indicated, emphasizing the connection between the electron spins.