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Calculated NMR Parameters (Chemical Shifts and Coupling Constants) of Cyclic C4

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Calculated NMR Parameters (Chemical Shifts and Coupling Constants) of Cyclic C

4

H

2

and C

4

H

4

Molecules Containing Carbene Centers, and of Some of their Boron Analoga, Using Density Functional Theory (DFT)

Bernd Wrackmeyer

Anorganische Chemie II, Universit¨at Bayreuth, D-95440 Bayreuth, Germany Reprint requests to Prof. Dr. B. Wrackmeyer. E-mail: b.wrack@uni-bayreuth.de Z. Naturforsch. 59b, 37 – 43 (2004); received October 24, 2003

Singlet state structures of small, cyclic hydrocarbons which can result from the addition of molec- ular dicarbon (C2) to ethyne (HC≡CH) or ethene (H2C=CH2) have been calculated (B3LYP/6- 311+G(d,p) level of theory), and were found to contain carbene centres. Some structures of analogous boranes (replacement of the carbene centers by BH fragments) were also calculated. The computa- tion of NMR parameters such as chemical shiftsδ13C andδ11B, and coupling constants1J(13C,1H),

1J(11B,1H), J(13C,13C) and J(13C,11B) shows that these data can be used for the discussion of the bonding situation. The presence of inverted carbene centers is clearly indicated by the increased13C nuclear magnetic shielding. Scalar13C-13C spin-spin coupling involving carbene centers are fre- quently dominated by spin-dipole and spin-orbital interactions.

Key words: Carbenes, Cyclic Hydrocarbons, Boranes, MO Calculations, NMR Parameters

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