Of course, I (everyone discussing in here) got what Dan said, and I also agree what he said.
About the triplet and singlet forms, they should be interchangable, so we can regard it as aromatic.
My bad! I just read what a couple of people wrote before I posted, dismissing the carbene as antiaromatic, and got a little bit worked up lol!
Another thing in favour of the singlet state in D, as well as the aromaticity, is the smaller bond angles in the molecule, which allow a greater space than normal for the electrons in the sp
2 orbital, so the "incentive" for the electrons to be in the triplet state is reduced further. Also, the general idea of the triplet state being favoured (due to stability) is useful, sometimes, but useless when there are electron-rich substituents on the carbene molecule, like in :CCl
2, where the electrons would be in the singlet state (but, by coincidence :CCl
2 is formed in the singlet state!).
Sorry for going on about carbenes, I just find them really interesting! [Edit: especially the Arndt-Eistert synthesis, and the Hofmann rearrangement!]
I wonder where is the source of this question!
So do I! There seems to be so many mistakes, though, in chemistry books nowadays. I've even found at least 3 'chemistry' errors in my organic chem book (the Clayden, Greeves, Warren, Wothers one), and my current A-Level book has at least 6 'chemistry' errors in it, one being half a page devoted to a mechanism (acid catalysed halogenation of acetone), which is entirely wrong! When my teacher tried to write out the mechanism out for that reaction last year he wrote the one in the book, and without reading up about this reaction I could tell it looked wrong, and suggested a mechanism which happened to be right after checking it out afterwards. Good thing you don't need to know that mechanism for the A-Level, the book was just trying to demonstrate the rate equation and its relation to the RDS.
I think there seems to be a lack of chemistry book editors- I am yet to find a chemistry book without a mistake in it!