Conjugate: compounds radicals

Alkali metal reduction is a widely employed method for the preparation of radicals derived from various classes of conjugated compounds such as hydrocarbons, heterocycles, nitro compounds, quinones, and nitriles. For... 

Uv-absoiption of carbonyl compound radical-anions and values of pK, for their conjugate acids... 

Conjugated compounds undergo a variety of reactions, many of which involve intermediates that retain some of the resonance stabilization of the conjugated system. Common intermediates include allylic systems, particularly allylic cations and radicals. Allylic cations and radicals are stabilized by delocalization. First, we consider some reactions involving allylic cations and radicals, then (Section 15-8) we derive the molecular orbital picture of their bonding. 

Cyclopropyl ketones (29) behave as weakly conjugated compounds, with significant orbital overlap between one ty-bond (or sometimes two) of the cyclopropane ring and the jr-orbital of the carbonyl group (p. 242). The three-membered ring is reduced by lithium in liquid ammonia, with rupture of whichever cr-bond most effectively overlaps the carbonyl tt-orbital [280]. The reduction probably involves transfer of an electron to the jS -carbon atom of this cr-bond, so that conjugative overlap can be maintained during a smooth transition to the species (30) which is both a carbanion and a resonance-stabilised enolate radical. A second electron trans-... 

Electrochemical modulated infrared (ir) spectroscopy has been used to obtain in situ spectra of the radical anion of benzophenone [5], There is a red shift of the vibrational modes of the benzene rings and considerable loosening of the carbonyl bond. Carbonyl compound radical anions are protonated on the oxygen center. The conjugate acids of alkanones and alkanals have pKg values [6] in the range 11-12, while those from conjugated aromatic carbonyl compounds [7] are in the range 8-10. 

Expected stationary state may be good approximation for calculation of kinetics of reaction flow. Mechanism of inhibition by azomethine conjugated compounds is accompanied by the break of multiple carbon-nitrogen bond and addition of radical. In the case of low-molecular azomethines separation of hydrogen atom and addition of radical to a -carbon atom take place ... 

Oxidation causes the formation of hydroperoxides and conjugated compounds, which by cleavage give aldehydes, alcohols, ketones, lactones, acids, esters, and hydrocarbons. Radical mechanisms lead to the formation of dimers, other oligomers, and oxidized TAG. The latter have one or more acyl group with an extra oxygen (hydroxy, keto, epoxy derivatives). Other oxidation products are TAG with short-chain fatty acyl and n-oxo fatty acyl groups. 

TREPE represents the conjugation stabilization or destabilization that one r-electron contributes to the molecular r-system. TRE values were computed for a large variety of conjugated compounds, including conjugated ions, radicals, and ion radicals, coumarins, thiocoumarins, and bridged heteroannulenes. Selected TRE and TREPE values for conjugated hydrocarbons are presented in Table 14. 

Considerable attention has been paid to nonclassical thermal cyclization of enediynes leading to high-aromatic rr-conjugated molecules. These reactions include cyclization promoted by organometallic compounds, radicals, electrophiles, and nucleophiles. 

It resembles tetracyanoethylene in that it adds reagents such as hydrogen (31), sulfurous acid (31), and tetrahydrofuran (32) to the ends of the conjugated system of carbon atoms suffers displacement of one or two cyano groups by nucleophilic reagents such as amines (33) or sodiomalononittile (34) forms TT-complexes with aromatic compounds (35) and takes an electron from iodide ion, copper, or tertiary amines to form an anion radical (35,36). The anion radical has been isolated as salts of the formula (TCNQ) where is a metal or ammonium cation, and n = 1, 1.5, or 2. Some of these salts have... 

Reduction of a conjugated enone to a saturated ketone requires the addition of two electrons and two protons. As in the case of the Birch reduction of aromatic compounds, the exact order of these additions has been the subject of study and speculation. Barton proposed that two electrons add initially giving a dicarbanion of the structure (49) which then is protonated rapidly at the / -position by ammonia, forming the enolate salt (50) of the saturated ketone. Stork later suggested that the radical-anion (51), a one electron... 

In order to understand the physical properties and reactivity patterns of S-N compounds it is particularly instructive to compare their electronic structures with those of the analogous organic systems.On a qualitative level, the simplest comparison is that between the hypothetical HSNH radical and the ethylene molecule each of these units can be considered as the building blocks from which conjugated -S=N- or -CH=CH-systems can be constructed. To a first approximation the (j-framework of... 

---