Homolysis

About: Homolysis is a research topic. Over the lifetime, 4305 publications have been published within this topic receiving 91400 citations.

Transition-metal-centered radicals in organic synthesis. Titanium(III)-induced cyclization of epoxy olefins

Abstract: We wish to report a solution to this problem which allows the direct synthesis of functionalized cyclopentane derivatives. This new reaction is based on an analogy to the extremely facile rearrangement of cyclopropylmethyl radical to homoallyl radical (eq 2). A a-complex of an epoxide with a paramagnetic transition metal4 having a half-filled (*-symmetry) d orbital represents an electronic analogue of the cyclopropylmethyl moiety. By analogy to eq 2, release of ring strain might be expected to drive the homolytic C-0 bond cleavage in eq 3.

An unusually stable thionitrite from N-acetyl-D,L-penicillamine; X-ray crystal and molecular structure of 2-(acetylamino)-2-carboxy-1,1-dimethylethyl thionitrite

Abstract: N-Acetyl-D,L-penicillamine (1) was converted by HNO2 into a thionitrite (3) which was stable as a solid and atypically so even in solution; X-ray structural parameters are given for (3), and both homolytic and heterolytic reactions are described.

Study of the solvent effect on the enthalpies of homolytic and heterolytic N–H bond cleavage in p-phenylenediamine and tetracyano-p-phenylenediamine

Abstract: In this article, we have studied p-phenylenediamine (PPD) and tetracyano-p-phenylenediamine (TCPPD) molecules in order to study the effect of CN groups and the solvent effect on the enthalpies of homolytic and heterolytic N–H bond cleavage. Geometries of the molecules and reaction enthalpies related to hydrogen atom transfer, single electron transfer–proton transfer (SET–PT) mechanism and sequential proton loss electron transfer (SPLET) mechanisms were studied using DFT/UB3LYP/6-31++G∗∗ method. Ab initio MP2/6-31++G∗∗ method was used as the reference for the geometry calculation of the two molecules in vacuum. Solvent contribution to the enthalpies was computed employing integral equation formalism IEF-PCM method. Obtained results show that solvent is able to cause significant change in the reaction enthalpies of the stepwise SET–PT and SPLET mechanisms of hydrogen splitting-off from NH2 group. This may result in the change in thermodynamically preferred mechanism. Solvents also attenuate the CN-substituent effect in the case of SET–PT and SPLET mechanisms.

Ab initio evaluation of the thermodynamic and electrochemical properties of alkyl halides and radicals and their mechanistic implications for atom transfer radical polymerization.

Abstract: High-level ab initio molecular orbital calculations are used to study the thermodynamics and electrochemistry relevant to the mechanism of atom transfer radical polymerization (ATRP). Homolytic bond dissociation energies (BDEs) and standard reduction potentials (SRPs) are reported for a series of alkyl halides (R−X; R = CH2CN, CH(CH3)CN, C(CH3)2CN, CH2COOC2H5, CH(CH3)COOCH3, C(CH3)2COOCH3, C(CH3)2COOC2H5, CH2Ph, CH(CH3)Ph, CH(CH3)Cl, CH(CH3)OCOCH3, CH(Ph)COOCH3, SO2Ph, Ph; X = Cl, Br, I) both in the gas phase and in two common organic solvents, acetonitrile and dimethylformamide. The SRPs of the corresponding alkyl radicals, R•, are also examined. The computational results are in a very good agreement with the experimental data. For all alkyl halides examined, it is found that, in the solution phase, one-electron reduction results in the fragmentation of the R−X bond to the corresponding alkyl radical and halide anion; hence it may be concluded that a hypothetical outer-sphere electron transfer (OSET) in ...