Construction Principles of "Hyparenes": Families of Molecules with Planar Pentacoordinate Carbons
Zhi-Xiang Wang,*
Paul von
Ragué Schleyer
Density-functional theory calculations predict that three
borocarbon units with planar pentacoordinate carbons
C3B3,
C2B4, and
CB5, can replace the (CH)3
subunits in aromatic or even in antiaromatic hydrocarbons to construct
"hyparenes" (families of molecules with planar pentacoordinate
carbons). These borocarbon units contribute two, one, and zero
electrons, respectively, to the parent pi system. Depending on the
choice of these units, the hyparenes (judging from computed
proton and nucleus-independent chemical shifts), can maintain or can
interconvert the aromatic or antiaromatic character of the parent
compounds. The hyparenes are low-lying local minima with normal
carbon-boron, boron-boron, and carbon-carbon bond lengths. The
multicenter bonding in the hyparenes involves contributions of partial
sigma and partial pi bonds to the planar pentacoordinate carbons; the
octet rule is not violated. Borocarbon species, for which there is some
mass spectrometric evidence, might be observed and identified, for example, in matrix isolation by vibrational spectroscopy.
Center for Computational Quantum Chemistry, Computational
Chemistry Annex, University of Georgia, Athens, GA 30602-2525, USA.
*
Permanent address: Graduate School at Beijing, University of
Science and Technology of China, Academia, Sinica, Beijing 10039, People's Republic of China.
To whom correspondence should be addressed. E-mail:
schleyer{at}chem.uga.edu
