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High-level ab initio calculations (MP4sdtq/6-31 l+G**//MP2/6-31G*) predict classical stmctures for monomeric lithioborane and the dimethyl, diamino, and difluoro derivatives. A structure with the lithium cation bridging one boron oxygen bond is computed as the most stable structure for dihydroxylithioborane. For this compound, an "inverted" structure is indicated to be viable. The singlet state of the boryl anion is only marginally more stable than the triplet at levels up to CCSD(T)/6-311 +G(3df,2pd), but interaction with a lithium cation stabilizes the singlet more than the triplet by about 20 kcal/mol. Reaction of lithioboranes with formaldehyde, as a model for carbonyl compounds, is predicted to proceed via nucleophilic attack of the boryl anion moiety, through a very early transition structure, to give a B-C-O three-membered-ring product.

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