Computational Studies of Electron Affinities, Acidities, and Bond Dissociation Energies of Boron-Containing Species:  The CH3(CH2) n -1BH2, CH2F(CH2) n -1BH2, and CH3(CH2) n -1BHF Series

• Published in: Organometallics 2007-03, Vol.26 (7), p.1599-1606
• Main Authors: Damrauer, Robert, Pusede, Sally E, Custer, Thomas C
• Format: Article
• Language: English
• ISSN: 0276-7333; 1520-6041
• DOI: 10.1021/om0610501

Computational studies of three series of boron-containing compounds, CH3(CH2) n -1BH2, CH2F(CH2) n -1BH2, and CH3(CH2) n -1BHF, have been carried out to probe the structural characteristics of the parent compounds and the radicals and anions derived by loss of their terminal C−H. The energies of these species yield electron affinities, acidities, and bond dissociation energies that are explained in terms of the structural characteristics, which vary with the value of n. One-carbon species are considered in terms of hyperconjugative effects. The radical species with n > 1 reveal important structures with strong tendencies for termini to interact. Carbon 2p radicals and empty 2p boron centers interact to give a cyclic radical species for BH2CH2CH2 and BH2CH2CHF and bent radicals with short distances between the termini for larger values of n. The bent and zigzag BH2(CH2) n -1CH2 radicals for n ≥ 3 are quite close in energy. All anions with n ≥ 2 are cyclic and considerably lower in energy than zigzag species. Single-point energies of parent, radical, and anionic species allow the determination of electron affinities (EA), acidities (ΔH acid), and bond dissociation energies (BDE). The EAs have a noticeable break between n = 3 and 4, a consequence of the strain energy of the n = 2 and 3 anions. The ΔH acid values exhibit trends also related to the strained nature of the n = 2 and 3 anions. The values of the terminal C−H BDEs are typical of C−H bonds with the exception of the CF-substituted series, where the somewhat smaller values indicate the C−H bond-weakening effect of fluorine substitution.