| Abstract
| - The bicyclic alkenylidenes 9 (bicyclo[3.2.1]oct-2-en-8-ylidene) and 17 (bicyclo[3.3.1]non-2-en-9-ylidene)were claimed to be stabilized foiled carbenes. Our B3LYP and MP2 computations confirm previousexperimental data. Moreover, they show that these carbenes are very reactive and rearrange rapidly,mainly through a 1,2-vinyl shift by overcoming a low barrier (1.2 to 5.4 kcal/mol). This is in contrast tothe high barriers (up to 30 kcal/mol) predicted for the same type of rearrangements in norborn-2-en-7-ylidene derivatives. In 17 and bicyclo[4.1.1]oct-2-en-7-ylidene (23), the divalent carbon atom is evenbent away from the double bond!
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