4348-35-0Relevant academic research and scientific papers
Homolytic Reactions of Ligated Boranes. Part 11. Electron Spin Resonance Studies of Radicals Derived from Primary Amine-Boranes
Kirwan, J. Nicolas,Roberts, Brian P.
, p. 539 - 550 (2007/10/02)
Photochemically generated t-butoxyl radicals react with the primary amine-boranes RNH2->BH3 (R = Me or But) to form, initially, the nucleophilic amine-boryl radical RNH2->BH2, which subsequently abstracts hydrogen from the parent amine-borane to give the more stable isomeric aminyl-borane radical RNH->BH3.The amine-boryl radicals can be intercepted by alkyl bromides or chlorides or by nitriles, with which they react by halogen-atom abstraction or by addition to the CN group to give iminyl radicals, respectively.The e. s. r. spectra of the aminyl-borane radicals show the presence of extensive hyperconjugative delocalisation of the unpaired electron onto the BH3 group .Monoalkylaminyl-borane radicals react readily with alkenes, with arenes, and with conjugated or cumulated dienes to transfer a β-hydrogen atom from boron to give alkyl, cyclohexadienyl, or allyl radicals, respectively.Hydrogen atom transfer to alkenes from the electrophilic MeNH->BH3 takes place with high regioselectivity to give the more stable alkyl radical when two adducts are possible; the rate of transfer increases as the ionisation potential of the alkene decreases along the series CH2=CH2 BH3 to give the isopropyl radical was determined to be ca. 2 x 103 dm3 mol-1 s-1 at 282 K.Competition experiments have been carried out to determine the relative rates of the various reactions undergone by RNH2->BH2 and RNH->BH3.The results are interpreted with the aid of ab initio molecular-orbital calculations at the 6-31G level for RNH2->BH2, RNH->BH3, RNH2->BH3, and RNHBH2 (R = H or Me), together with similar calculations for the isoelectronic organic counterparts in which the NB moiety is replaced by a CC grouping.
Thermolysis of Highly Congested tert-Butyldialkylcarbinols with Bridgehead Substituents: Molecular Mechanics Treatment of Radical-Forming Processes
Lomas, John S.,Dubois, Jacques-Emile
, p. 4505 - 4511 (2007/10/02)
The termolysis rate constants of eight tertiary alcohols, R1R2R3COH, bearing a tert-butyl group (R3) with various combinations of tert-butyl, tert-amyl, 1-adamantyl, 1-bicyclooctyl, and 1-norbornyl substituents at the tertiary carbon have been measured in dodecane.The effects of these groups on the rate of tert-butyl cleavage are roughly additive and in quantitive agreement with their known steric requirements, exept for tert-amyl which appears to be smaller than E's would suggest.Activation energies can be interpreted in terms of strain energy changes, calculated by molecular mechanics; several different models are used to describe the reaction and, where possible, three different force fields.The most satisfactory description of the reaction is based upon Allinger's MM2 force field, with the assumption that the radical intermediate, R1R2COH, can be represented by the corresponding dialkylcarbinol.Product analysis shows that the tert-butyl radical is formed in preference to any other, except tert-amyl, but small amounts of products arising from C-Ad fission are detected in certain cases.This result, in accordance with previous molecular mechanics calculations on thermolysis rates, indicates that the radical strain energies in bridgehead systems must be slightly greater than those of the corresponding alkanes but substantially less than those of the related carbocations.
