Bond distances radicals

Are the carbon-carbon bond distances in allyl cation, allyl radical allyl anion all similar, or are they significantly... 

Use of the Hammond Postulate requires that the reverse reactions both be fast. Obtain energies for the transition states leading to 1-propyl and 2-propyl radicals ipropane+Br end and propane+Br center), and draw a reaction energy diagram for each (place the diagrams on the same axes). Is use of the Hammond Postulate justified Compare the partial CH and HBr bond distances in each transition state to the corresponding distances in propane and hydrogen bromide, respectively. Does the Hammond Postulate correctly predict which bond distances will be most similar Explain. 

Examine the electrostatic potential map and spin density surface of Q radical anion (Q ). Draw all of the resonance contributors needed to account for these data. Examine the CO bond distances and spin density surface of QH radical (QH ). Draw all of the resonance contributors needed to account for these data. 

Molecular orbital calculations, whether by ab initio or semiempirical methods, can be used to obtain structures (bond distances and angles), energies (such as heats of formation), dipole moments, ionization energies, and other properties of molecules, ions, and radicals—not only of stable ones, but also of those so unstable that these properties cannot be obtained from experimental measurements." Many of these calculations have been performed on transition states (p. 279) this is the only way to get this information, since transition states are not, in general, directly observable. Of course, it is not possible to check data obtained for unstable molecules and transition states against any experimental values, so that the reliability of the various MO methods for these cases is always a question. However, our confidence in them does increase when (1) different MO methods give similar results, and (2) a particular MO method works well for cases that can be checked against experimental methods. ... 

The second case is illustrated in Figure 6, where the total energy dependences on the C—C bond distance in ethylene radical ions are presented. 

Another example of rr-delocalized radical is cyclopentadienyl 43, which was reported by Sitzmann et al. to be rendered persistent and crystalline by derivatization with /io-propyl groups as in radical 44 (Fig. 7.19). ° "° An interesting feature in the X-ray structure of 44 is that the /io-propyl groups adopt a paddlewheel-like conformation, also showing disorder in the crystal. The bond distances show that the radical is not Dsh symmetric, but that it is slightly distorted (C1-C2 = 1.412 A, C2-C3 = 1.401 A). Radical 44 also packs in a columnar motif with rings eclipsing each other... 

The lattice-stabilization effects allow the isolation of [MF6]- salts (M=As, Sb) of [S3N2]2+ in the solid state from the cycloaddition of [SN]+ and [S2N]+ cations in S02.66 The S-S and S-N bond distances in the planar, monomeric dication are shorter than those in the dimeric radical cation dimer, as anticipated for the removal of an electron from a n orbital. 

Figure 16. Structural data of [Cr(LBuMel)]° and [Cr(LBuMet )]+ showing the C—C and C—O bond distances in angstroms of (a) the coordinated phenolato groups and (b) the coordinated phenoxyl in [Cr(LBuMet )]+ (154). In (c), the calculated metrical details of the freep-methoxyphenoxyl radical (157) are displayed.

In theoretical work, the initial steps in the polymerization of 1,1-dicyano-, 1,1-difluoro-, and 1,1-dimethyl-cyclopropanes by reaction with H, OH, and Me have been modelled by ab initio methods. " Other ab initio MO calculations for the reactions of H, Me, Ft, j-Pr, and r-Bu with a variety of silanes and germanes have been carried out. The results indicate that the attacking and leaving radicals adopt an almost co-linear arrangement. Bond distances and energy barriers were predicted for the reactions studied. 

The results of the careful hypersurface calculations were surprising hydrazine with its dihedral angle ui=90° and an NN bond distance of 145 pm, on loss of one out of its 14 valence electrons, should form a completely planar (D2h) radical cation with the NN bond length shrinking by 17 pm ( ) to 128 pm ( ). Luckily enough, we dared to publish this hard-to-believe result (23), which a few months later has been completely confirmed by S.F. Nelson and collaborators (25), who succeeded in isolating crystals of the tetraalkyl hydrazine radical cation (3) and obtaining its X-ray structure, which exhibits an NN bond distance of 127 pm, i. e. close to the hypersurface prediction ... 

For this reaction, the reaction coordinate is simply the Si-H bond distance. Since the reverse of this reaction is radical-radical recombination and should have no activation energy barrier, the E for forward reaction would be expected to be AH,. 

As seen, cyclophane structures shown in Schemes 1.4b through 1.4e have the following unique feature The through-bond distance within the paracyclophane fragment is held constant, whereas the spatial distance between the ion-radicalized and neutral moieties is changed. Therefore, the relative importance of through-bond and through-space mechanisms for intramolecular electron transfer can be learned directly from experimental data on these molecules. 

It is well known that crystal and electronic structures are interdependent and define the reactivity of chemical substances. In Section 1.4.2, it was noted that copper-porphyrin complex gives cation-radicals with significant reactivity at the molecular periphery. This reactivity appears to be that of nucleophilic attack on this cation-radical, which belongs to n-type. The literature sources note, however, some differences in the reactivity of individual positions. A frequently observed feature in these n-cation derivatives is the appearance of an alternating bond distance pattern in the inner ring of porphyrin consistent with a localized structure rather than the delocalized structure usually ascribed to cation-radical. A pseudo Jahn-Teller distortion has been named as a possible cause of this alternation, and it was revealed by X-ray diffraction method (Scheidt 2001). 

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