Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Structure and Bonding of Radicals

Spectroscopic data can be used to distinguish between planar and nonplanar rapidly inverting radical centers. The hyperfine coupling constant a in the methyl radical is 23.0 G, which is a typical value for the splitting of an EPR signal by protons attached to a radical center. Theoretical analysis of the spectrum suggested that the methyl radical is probably flat, although a deviation from planarity of 10-15° could not be ruled out There is also spectroscopic evidence that the methyl radical in the gas phase is essentially planar. Thus, the methyl radical is conveniently described by sp hybridization with the unpaired electron located primarily in the p orbital. [Pg.109]

Not only are fluoro-substituted radicals nonplanar, but alkyl substituted radicals are also found to be nonplanar. An explanation for the nonplanar nature of hydrocarbon radicals was provided by Paddon-Row and Houk, who ascribed the pyramidalization of the radical center to two effects (i) increased staggering of [Pg.109]

When bonds break and one atom obtains both bonding electrons the process is called heterolysis and the products are ions. When bonds break and the atoms get one bonding electron each, the process is called homolysis and the products are radicals, which may be atoms or molecules, and contain an unpaired electron (Eq. (4.1))  [Pg.111]


J. M. Rawson and F. Palacio, Magnetic Properties of Thiazyl Radicals, Structure and Bonding, 100, 93 (2001). [Pg.12]

Since these basic facts became known, a tremendous amount of research has been done on the structures and behaviors of these important substances. There has also been much research on the synthesis and study of other chain polyelectrolytes, containing hydrogen-bond-forming radicals (R) more-or-less like those in the natural nucleic acids. The primary aim of this research is, of course, to relate the behavior of the synthetic materials to the behavior of the natural ones. Okubo and Ise here present an excellent discussion on this research. [Pg.192]

In recent years, the amount of research time devoted to materials chemistry has risen almost exponentially and sulfur-based radicals, such as the charge-transfer salts based upon TTF (tetrathiafulvalene), have played an important role in these developments. These TTF derivatives will not be discussed here but are dealt with elsewhere in this book. Instead we focus on recent developments in the area of group 15/16 free radicals. Up until the latter end of the last century, these radicals posed fundamental questions regarding the structure and bonding in main group chemistry. Now, in many cases, their thermodynamic and kinetic stability allows them to be used in the construction of molecular magnets and conductors. In this overview we will focus on the synthesis and characterisation of these radicals with a particular emphasis on their physical properties. [Pg.734]

Os3(CO)i2, nine products were obtained. Three of these were identified as the substituted adducts Os3(CO)12(Ph3P)i2- Gc = 1, 2, or 3), but for others, the fission of C-H and C-P bonds had occurred to yield a variety of compounds in which there were radical variations in the structure and mode of bonding of the triphenylphosphine group. Figure 29 shows details of the structures of six of these complexes. As indicated above, significant ligand rearrangements have taken place. [Pg.302]

Concerning their structure and reactions, organic radical cations have been the focus of much interest. Among bimolecular reactions, the addition to alkenes and their nucleophilic capture by alcohols, which lead to C—C and C—O bond formation, respectively have been investigated in detail. Unimolecular reactions like geometric isomerization and several other rearrangements have also attracted attention. [Pg.201]

The transfer constants for various compounds are shown in Table 3-6. These data are useful for the information they yield regarding the relationship between structure and reactivity in radical displacement reactions. Aliphatic hydrocarbons such as cyclohexane with strong C—H bonds show low transfer constants. Benzene has an even lower Cs value because of... [Pg.246]

The major carbon centered reaction intermediates in multistep reactions are carboca-tions (carbenium ions), carbanions, free radicals, and carbenes. Formation of most of these from common reactants is an endothermic process and is often rate determining. By the Hammond principle, the transition state for such a process should resemble the reactive intermediate. Thus, although it is usually difficult to assess the bonding in transition states, factors which affect the structure and stability of reactive intermediates will also be operative to a parallel extent in transition states. We examine the effect of substituents of the three kinds discussed above on the four different reactive intermediates, taking as our reference the parent systems [ ]+, [ ]-, [ ], and [ CI I21-... [Pg.105]

Extensive reviews of the effects of fluonnation on structure and bonding are available [75, 76, 77], and only the characteristic trends in bond strengths will be covered here. The bond energies cited are average values corrected for the revised heats of formation of alkyl radicals [781, but their precision is seldom better than 2 keal/mol for the fluoro compounds. [Pg.990]

The 2,2,6,6-tetramethylpiperidinoxyl radical (TEMPO) was first prepared in 1960 by Lebedev and Kazarnovskii by oxidation of its piperidine precursor.18 The steric hindrance of the NO bond in TEMPO makes it a highly stable radical species, resistant to air and moisture. Paramagnetic TEMPO radicals can be employed as powerful spin probes for elucidating the structure and dynamics of both synthetic and biopolymers (e.g., proteins and DNA) by ESR spectroscopy.19 Unlike solid-phase 1H-NMR where magic angle spinning is required in order to reduce the anisotropic effects in the solid-phase environment, solid-phase ESR spectroscopy can be conducted without specialized equipment. Thus, we conducted comparative ESR studies of various polymers with persistent radical labels, and we also determined rotational correlation times as a function of... [Pg.371]

In the following, we examine the nature of the central bond between the CX radicals in 4 and 5 (X = N, P). To what extent can this bond be considered to be a simple a electron pair bond Does it bonding make a significant contribution What exactly determines the degree to which the 2c-2e bond interferes with other electrons, and how does this affect molecular structure and bond strength The discussion of these questions is based on our DFT investiga-... [Pg.35]


See other pages where Structure and Bonding of Radicals is mentioned: [Pg.107]    [Pg.107]    [Pg.109]    [Pg.264]    [Pg.107]    [Pg.107]    [Pg.109]    [Pg.264]    [Pg.401]    [Pg.66]    [Pg.335]    [Pg.84]    [Pg.84]    [Pg.135]    [Pg.272]    [Pg.64]    [Pg.634]    [Pg.239]    [Pg.294]    [Pg.731]    [Pg.1312]    [Pg.74]    [Pg.167]    [Pg.17]    [Pg.87]    [Pg.494]    [Pg.244]    [Pg.413]    [Pg.254]    [Pg.224]    [Pg.67]    [Pg.31]    [Pg.517]    [Pg.287]    [Pg.158]    [Pg.577]    [Pg.171]    [Pg.158]    [Pg.577]   


SEARCH



Bonding and radicals

Bonds and structure

Radicals bonding

Radicals structure

Structure and bonding

© 2024 chempedia.info