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A detailed examination of aqueous Si complexation by alditols and aldonic acids was conducted using high-sensitivity 29Si NMR spectroscopy of isotopically enriched solutions combined with theoretical modeling. Contrary to previous thinking, we have established that aliphatic polyols do not require a threopair of hydroxy groups to form hypercoordinated Si complexes, although formation constants may be orders of magnitude higher if they are present. Thirteen distinctly different molecular assemblages containing 4-, 5-, or 6-coordinate Si centers have been identified, with significant concentrations of 5-coordinate Si bis-ligand complex being detected even under biologically relevant solution conditions.

Substituents modulate reactions, but their effects are commonly described by using proxies to their functional group properties. Substituent descriptors from the quantum theory of atoms in molecules, which are true functional group properties, are related here to these proxies, which have historically had chemically relevant meaning. Due to the large number of descriptors, multivariate analysis is used to intuit their significance. Multiple linear regression, principal component, and partial least squares regression analyses highlight that these substituent descriptors contain similar information to the proxies while being intrinsic, predictable substituent properties. Sources of error limiting quantitative reproduction of the proxy data include transferability, experimental accuracy, and solvation issues.

Extensive multireference CI calculations using a contracted 6s5p3d1fGaussian basis set on the B and N atoms indicate that the X2∑+, A2Π, and B2∑+states of BN−are bound with respect to the electron attachment BN + e−. The 14∑+, 14Δ, 14∑−, and 14Π states of BN−are resonant states, all autodetaching into neutral BN. The electron affinity X3Π → X2∑+is predicted to be 2.84 eV (with a best estimate of 3.10 eV). Other features studied for BN−include the infrared spectrum of the X2∑+ground state as well as the electronic radiative properties involving the excited states A2Π and B2∑+. The present study supports a X3Π ground state for BN, with a1∑+lying about 0.03 eV higher. As an alternative to optical spectroscopy on BN, experimental studies of the photodetachment spectrum of BN−are proposed in order to find the ordering and energetic separation of the lowest 3Π and 1∑+states of BN.

A combination of density-functional theory and natural resonance theory has been used to show that a complete description of the electronic structure of nitrilimines, R1CNNR2, requires four resonance structures propargylic, allenic, 1,3-dipolar and carbenic; appropriate substituents were shown to enhance the carbene character of nitrilimines to the point where they may be considered stable carbenes.

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