August 2010

Hexapentaenylidene (H2C6)

Hexapentaenylidene (H2C6) was observed in 1996 by Langer et al. in TMC-1 using the NASA Deep Space Network 70 m antenna in Goldstone, California. Two additional studies published in 1997 by McCarthy et al. (1, 2) provide further details about the laboratory measurements for H2C6.

H2C6 is a cumulene carbene. Other H2Cn molecules that have been observed in space include propadienylidene (H2C3) and butatrienylidene (H2C4). The C5 member of the family, pentatetraenylidene (H2C5), has not been observed to date in the interstellar medium.

In H2Cn molecules, only the terminal C atom is divalent instead of tetravalent. The double bonding looks like this, with the π bonds alternating in and out of the plane defined by the H atoms:

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