Spin-Polarized Conceptual Density Functional Theory Study of the Regioselectivity in Ring Closures of Radicals (original) (raw)

A theoretical study on the internal rotation and hyperfine structures of the ethyl radical (CH3-CH2)

Chemical Physics, 1991

It is contirmed by the UMP2/6-3 IG** level of calculation, that the zero-point vibrational energy dominates in determining the conformational preference and the extremely low barrier to internal rotation in the ethyl radical. The isotropic hypertine coupling constants of hydrogens and carbons of the ethyl radical have been calculated using an extended ab initio single-or multi-reference CI wavefunction (SR-CI or MR-CI). The spin density at each nucleus of interest has been calculated as a function of the basis sets and the CIdimensions. The influence of the internal rotation of the methyl group and the inversion of the methylene group on the hyperflne coupling constants has also been studied. Furthermore, the anisotropic hypertine coupling constants (dipolar term) have been calculated and compared with available experimental values.

The Degree of Rotation Independence of Conjugation of S−N Bonds

The Journal of Physical Chemistry A

The electron delocalization in π-electron systems is frequently described qualitatively by the concept of conjugation between formal double bonds separated by a formal single bond. In carbon compounds the optimum conjugation usually requires a rather strict, geometrical condition: the exact or near coplanarity of the participating carbon atoms. However, the geometrical conditions are much less strict for third-row atoms if the bonding involves valence-shell d orbitals. In some sulfur compounds, such as N-sulfonylsulfilimines, the conjugation is almost unaffected within large ranges of bond-rotation angles, which amounts to rotationindependent conjugation. On the basis of the indications of earlier, limited studies using only minimal basis set and no geometry optimization, in the more extensive present study Density Functional Theory B3LYP calculations using 6-31G* basis set provide more reliable evidence for such flexible conjugation in some sulfur compounds and give an explanation for the experimentally observed interconversion of chiral conformers of N-sulfonylsulfilimines.

1 1 7 M ay 1 99 7 Precision D eterm ination ofthe N eutron Spin Structure Function g

2021

K .Abe,T.Akagi,B.D.Anderson,P.L.Anthony,R.G .Arnold,T.Averett,H.R.Band,C.M . Berisso,P.Bogorad,H.Borel,P.E.Bosted,V.Breton,M .J.Buenerd,G .D.Cates,T.E.Chupp,S. Churchwell,K .P.Coulter,M .Daoudi,P.Decowski,R.Erickson,J.N.Fellbaum ,H.Fonvieille,R. G earhart,V.G hazikhanian,K .A.G ri oen ,R.S.Hicks,R.Holm es,E.W .Hughes,G .Igo,S.Incerti,J. R.Johnson,W .K ahl,M .K hayat,Yu.G .K olom ensky,S.E.K uhn,K .K um ar,M .K uriki,R. Lom bard-Nelsen,D.M .M anley,J.M arroncle,T.M aruyam a,T.M arvin,W .M eyer,Z.-E.M eziani,D. M iller,G .M itchell,M .O lson,G .A.Peterson,G .G .Petratos,R.Pitthan,R.Prepost,P.Raines,B. Raue,D.Reyna,L.S.Rochester,S.E.Rock,M .V.Rom alis,F.Sabatie,G .Shapiro,J.Shaw,T.B. Sm ith,L.Sorrell,P.A.Souder,F.Staley,S.St.Lorant,L.M .Stuart,F.Suekane,Z.M .Szalata,Y. Terrien,A.K .Thom pson,T.Toole,X.W ang,J.W .W atson,R.C.W elsh,F.W esselm ann,T.W right, C.C.Young,B.Youngm an,H.Yuta,W .-M .Zhang,and P.Zyla 1 Am erican University,W ashington,DC 20016

Application of electron spin resonance spectroscopy to problems of structure and conformation. XXVII. Cyclohexanone iminoxy radicals

Journal of the American Chemical Society, 1974

An analysis of long-range esr hyperfine splittings for a series of cycloheptane-1,2-semidiones allows the chair conformation to be assigned. Extended Hiickel calculations support the experimental hfs assignments. Numerous rigid biand tricyclic derivatives of cycloheptanesemidione showing long-range splittings in their esr spectra are described particularly in the bicyclo[3.2.l]octane-6,7-semidione, bicyclo[3.2.2]nonane-6,7-semidione, bicyclo[3.3.2]decane-9,lO-semidione, and bi-cycl0[4.2.1 ]nonane-3,4-semidione series. The possible conformations of bicyclo[4.l .O] heptane-3,4-semidione, bicyclo-[ 3.2.01 heptane-6,7-semidione, and bicycle[ 3.2.01 heptane-2,3-semidione are considered, and conformational assignments are made for bicyclo[4.2.l]nonane-3,4-semidione, bicyclo[3.2.2]nonane-6,7-semidione, and bicyclo[3.3.2]decane-10,1 l-semidione, all of which possess the cycloheptene ring in a boat conformation. Bicyclo[3.2.2]nonane-2,3-semidione appears to have a symmetrical conformation. The relative magnitudes of nonbonded interactions in bicyclic semidiones are discussed and compared.

Spin density distributions in some radical anions exhibiting restricted rotation about a carbon-carbon bond

Theoretical Chemistry Accounts, 1971

In the radical anions of styrene, 4-vinyl pyridine and p-fluoro-styrene it has been found earlier by ESR experiments that the two ortho protons, as well as the two meta protons of the six-membered ring are not equivalent. We have made a systematic theoretical study of these systems by using the unrestricted Hartree-Fock method. Satisfactory agreement with the experimental results has been obtained without invoking the so called “α effect” or “β effect”.

The Triplet–Singlet Gap in the m -Xylylene Radical: A Not So Simple One

Journal of Chemical Theory and Computation, 2014

or m-xylylene provides a model for larger organic diradicals, the triplet−singlet gap being the key property. In the present work this energy difference has been the object of a systematic study by means of several density functional theory-based methods including B3LYP, M06, M06-2X, HSE and LC-ωPBE potentials and a variety of wave function-based methods such as complete active space self consistent field (CASSCF), Multireference second-order Møller−Plesset (MRMP), difference dedicated configuration interaction (DDCI), and Multireference configuration interaction (MRCI). In each case various basis sets of increasing quality have been explored, and the effect of the molecular geometry is also analyzed. The use of the triplet and broken symmetry (BS) solutions for the corresponding optimized geometries obtained from B3LYP and especially M06-2X functionals provide the value of the adiabatic triplet−singlet gap closer to experiment when compared to the reported value of Wenthold, Kim, and Lineberger, (J. Am. Chem. Soc. 1997, 119, 1354 and also for the electron affinity. The agreement further improves using the full π-valence CASSCF(8,8) optimized geometry as an attempt to correct for the spin contamination effects on the geometry of the BS state. The CASSCF, MRMP, and MRCI, even with the full π valence CAS(8,8) as reference and relatively large basis set, systematically overestimate the experimental value indicating either that an accurate description must go beyond this level of theory, including σ electrons and higher order polarization functions, or perhaps that the measured value is affected by the experimental conditions.