text: Butyllithium converts a dibromo-cyclopropane to an allene through one of these intermediates in the Skattebøl rearrange- ment.
full_question: Butyllithium converts a dibromo-cyclopropane to an allene through one of these intermediates in the Skattebøl rearrange- ment. Reaction of a metal carbonyl complex with potassium intercalated in graphite then trimethylsilyl chloride forms these compounds in the Hegedus-Semmelhack procedure. One of these compounds is an intermediate in the stepwise mechanism of the Wolff rearrangement. Imidazole-2-ylidenes are examples of an unusually stable "n-heterocyclic" type of these compounds. A di-iodo methane complex with zinc whose reactivity resembles these compounds is used in the cyclopropanation of alkenes in the Simmons-Smith reaction. Transition metal complexes with these compounds can be either in a singlet or a triplet state, depending on whether they are of the Fischer or Shrock types. For 10 points, name these neutral carbon compounds that possess a lone pair of valence electrons.
first_sentence: Butyllithium converts a dibromo-cyclopropane to an allene through one of these intermediates in the Skattebøl rearrange- ment.
raw_answer: carbenes