Radical potential energies

Cao, J.R. George, M. Holmes, J.L. Fragmentation of 1- and 3-Methoxypropene Ions. Another Part of the [C4HsO] Cation Radical Potential Energy Surface. J. Am. Chem. Soc. Mass Spectrom. 1992, 3,99-107. 

An intriguing competition arises in the context of cation radical cycloadditions (as in the context of Diels-Alder cycloadditions) which involve at least one conjugated diene component. Since both cyclobutanation and Diels-Alder addition are extremely facile reactions on the cation radical potential energy surface, it would not be surprising to find a mixture of cyclobutane (CB) and Diels-Alder (DA) addition to the diene component in such cases. Even in the cyclodimerization of 1,3-cyclohexadiene, syn and anti cyclobutadimers are observed as 1 % of the total dimeric product. Incidentally, the DA dimers have been shown not to arise indirectly via the CB dimers in this case [58]. The cross addition of tw 5-anethole to 1,3-cyclohexadiene also proceeds directly and essentially exclusively to the Diels-Alder adducts [endo > exo). Similarly, additions to 1,3-cyclopentadiene yield essentially only Diels-Alder adducts. However, additions to acyclic dienes, which typically exist predominantly in the s-trans conformation which is inherently unsuitable for Diels Alder cycloaddition, can yield either exclusively CB adducts, a mixture of CB and DA adducts or essentially exclusively DA adducts (Scheme 26) [59]. 

Keywords Atmospheric chemistry Water reactions Bromine atoms OH radicals Potential energy surfaces Ab initio computations... 

Figure 8.15 HBN radical potential energy surfaces and selected energy levels of 2 and II symmetry. Adiabatic (red, black) and diabatic (violet, magenta) PES. 2D cut at linear geometries, crossing seam shown as a green line ID cuts along BN stretching coordinate for / BH and 6 fixed at 2.1A and 150°, respectively. The component of the A" symmetry of the 11 state shown as a blue line. Assignment based on plots and expansion coefficients of vibrational part of wavefunctions. AU values in cm levels showing resonances are marked.

A very good correspondence is found between the nature of the unimolecular lifetime distribution and the fraction of trajectories that are quasiperiodic. Surface VA, which has the most intrinsically non-RRKM lifetime distribution, also contains the largest fraction of quasiperiodic trajectories. The fraction of quasiperiodic trajectories is negligibly small for the surfaces with intrinsically RRKM lifetime distributions. A summary of our findings is given in Table 4. The A and B surfaces are the ones with the largest number of quasiperiodic trajectories, and these surface types are most similar to the ethyl radical potential energy surface. 

C. S. Sloane and W. L. Ease, Ethyl radical potential energy surface, Faraday Disc. Chem. Soc. 62 210 (1977). 

Detailed results will be presented for the potential surfaces pertinent to these four reactions. In particular we have computed the minimum-energy pathways. A less complete description of the formyl radical potential energy surface has appeared previously. ... 

Polyethylene (Section 6 21) A polymer of ethylene Polymer (Section 6 21) Large molecule formed by the repeti tive combination of many smaller molecules (monomers) Polymerase chain reaction (Section 28 16) A laboratory method for making multiple copies of DNA Polymerization (Section 6 21) Process by which a polymer is prepared The principal processes include free radical cationic coordination and condensation polymerization Polypeptide (Section 27 1) A polymer made up of many (more than eight to ten) amino acid residues Polypropylene (Section 6 21) A polymer of propene Polysaccharide (Sections 25 1 and 25 15) A carbohydrate that yields many monosacchande units on hydrolysis Potential energy (Section 2 18) The energy a system has ex elusive of Its kinetic energy... 

FIGURE 3. Qualitative energy model of a radical-anion pair in sulfoxides where A = CH3, C2H5 B = SOCH3, "SOC2H5 u is the potential energy R(AB) is the distance between A and B. Reproduced by permission of the authors from Reference 16. 

Figure 10. Three-dimensional potential-energy surface for the H + C2H3 C2H4 addition reaction. The lower left plot is taken in the symmetry plane of the vinyl radical. The other plots are taken in parallel planes at distances of O.S. O a.u. from the symmetry plane (1 a.u. = 0.52918 A). Solid contours are positive, dashed contours are negative, and the zero-energy contour (defined to be the energy of the reactant asymptote) is shown with a heavy sohd fine. The contour increment is 1 kcalmoU. Reproduced from [57] by pentrission of the PCCP Owner Societies.

Fig. 26.—Illustrative representation of the potential energy of the radical-monomer pair as a function of their distance of separation. See text for further explanation.

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