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Benzophenone, a material that is common in biomass and coal, resists pyrolysis up to 400 °C. However, when the compound is reduced with potassium metal in tetrahydrofuran (THF) followed by solvent removal, the C−H bonds, as well as the CO bond, are activated, and the solid K+C12H10CO•–·THF salt begins to gasify at less than 250 °C. The noncondensable (at liquid nitrogen temperature) gases consist of hydrogen and methane. Condensable pyrolysis products include the following: benzene, toluene, biphenyl, xylenes, diphenylmethane, and ethylbenzene. When the temperature is raised to 380 °C and held there for several hours, CO is also liberated. Isotopic labeling studies suggest that the CH4 comes from a carbene intermediate, and the CO does not originate from the carbonyl moiety of the ketyl.

EPR studies in tetrahydrofuran, reveal that the one electron reduction of 1-(9-methyl-9H-fluoren-9-yl)-4-methylbenzene via electron transfer from cesium metal produces an anion radical that has a large affinity for the cesium cation. The affinity of this anion radical for Cs+ is so great that it will actually "suck" the Cs+ (but not Na+ or K+) right out of the grasp of 18-crown-6, leading to a cation-assisted pi-stacked complex, where the s-orbital of the metal cation is simultaneously overlapped with the pi-clouds of the phenyl and fluorenyl moieties. At ambient temperature, proton- and cesium-electron coupling constants are rapidly (on the EPR time scale) modulated as a result of the simultaneous existence of two interconverting conformers having an averaged cesium splitting (a(Cs)) of about 1.6 G. The pi-s-pi-electronic coupling can be turned on or off via the addition or removal of cesium cations. Analogous pi-s-pi-electronic coupling is observed in the 1,4-bis(9-methyl-9H-fluoren-9-yl)benzene-cesium system.

The room temperature potassium reduction of 1,2,3-triscyclooctatetraeneoxypropane, in hexamethylphosphoramide (HMPA), yields an anion radical, which disproportionates so strongly to the dianion diradical that the anion radical cannot be observed via EPR. The dianion diradical has one unpaired electron in a primary and one in a secondary ring system, and it can be readily reduced to the corresponding trianion triradical. An analogous reduction of 1,2,3,4-tetrakiscyclooctatetraeneoxybutane does produce an observable anion radical, but it also is readily reduced to the system corresponding to one electron per eight-membered ring (the tetraanion tetraradical). These results and those obtained from systems containing two cyclooctatetraene (COT) moieties are explained in terms of the geometry changes COT undergoes upon one-electron reduction, the interactions between reduced and adjacent unreduced ring systems, and the electron- electron repulsion present in the polyanion polyradicals.

The anion radical of mono-bromo-[8]annulene was generated in the absence of ion association, and the EPR-measured spin densities can be explained in terms of the odd electron occupying MOs: Ψ4‘ = [2√(n2 + 1)]-1(ψ1 + nψ2 − ψ3 − nψ4 + ψ5 + nψ6 − ψ7 − nψ8) and Ψ5‘ = [2√(n2 + 1)]-1(ψ1 − nψ2 − ψ3 + nψ4 + ψ5 − nψ6 − ψ7 + nψ8) where n > 1. This anion radical subsequently disproportionates to its corresponding dianion and neutral molecule. The dianion then undergoes a loss of Br-, leaving the [8]annulenyl carbanion, which can abstract a proton from either HMPA or liquid ammonia. The pseudo-ortho-bromo-[8]annulenyl carbanion also loses Br- to give [8]annulyne, which can be stabilized in the form of its anion radical. The g value of the anion radical of [8]annulyne indicates that the extra strain energy due to the presence of the triple bond causes the two highest occupied MOs (degenerate in the anion radical of [8]annulene) to be slightly split.

The low-temperature (-100 degrees C) dehydrohalogenation of bromocyclooctatetraene followed by immediate electron-transfer yields a stable solution of the [8]annulyne anion radical. If the unstable [8]annulyne is reacted with itself, cyclobutadiene, or benzyne, the respective bi-[8]annulenylene, [6]annuleno[8]annulene, or [6]-[8]annulenylene can be trapped as their anion radicals via one-electron transfer. These condensation products were all obtained from simple [2 + 2] cycloaddition reactions. B3LYP/6-31G geometry optimizations were carried out, and the calculated spin densities were compared to the EPR spectral results obtained for the anion radicals of [6]annuleno[8]annulene, [8]annulyne, bi[8]annulenylene, and [6]-[8]annulenylene, and excellent agreement has been realized. This simple "one-pot" approach should be applicable to a wide range of such systems.

Electron paramagnetic resonance (EPR) studies have revealed that the steric interaction between the methyl hydrogens on a tert-butoxy substituent and the cyclooctatetraene (COT) ring system sterically induces a puckering of the eight-membered ring in the anion radical of tert-butoxy-COT. The induced nonplanarity of the COT ring system causes a large attenuation of the EPR coupling constants. Since the C-D bond length is slightly shorter than is the C-H bond length, replacement of the tert-butyl group with a tert-butyl-d(9) group results in less steric interaction and measurably larger electron proton coupling constants. The oscillation between the two close to planar alternating bond length (ABL) D(2d) conformers of the COT moiety was found to be extremely rapid (k10(12) s(-1)) and quantum mechanical tunneling is proposed to be involved.

The anion radicals of [18]annulene and of [6]annulene undergo Jahn-Teller distortions from the D 6 h conformations of their respective neutral molecules. The conformation of lowest energy for the anion radical of benzene has a C 2 e symmetry, and that for the anion radical of [18]annulene is D 2 h . The very rapid pseudo-rotation of the benzene C 2 r system causes the six protons of the benzene anion radical to appear as if they were equivalent in the EPR experiment. Fast pseudo-rotation rendering the uniform distribution of spin density in the [18]annulene anion radical system is prevented by the nonplanarity of the radical. Hence, the EPR spectrum of the [18]annulene anion radical must be interpreted in terms of a static (on the EPR time scale) D 2 h conformation, which pseudo-rotates over a C 2 h transition state. B3LYP calculations support these conclusions.

In contrast to the thermolysis of p-benzoquinone, which does not decompose until the temperature is over 800 degrees C, and then primarily yields vinylacetylene, the corresponding anion radical, precipitated from liquid ammonia [Na(+)(NH(3))C(6)H(4)O(2)(*-)], decomposes at 380 degrees C and fragments primarily into phenol, hydroquinone, ammonia, methane, carbon monoxide, hydrogen, and minor amounts of other simple compounds. When the benzoquinone is replaced with perdeuteriobenzoquinone, deuterium and hydrogen are randomly scrambled into the products, and both ND(3) and CH(4) are formed. When the hot pyrolysis container is completely sealed, preventing the escape of volatile materials, p-aminophenol, as opposed to phenol, is the major liquid product.

The anion radical of cyclooctatetraene (COT) must undergo a Jahn−Teller distortion from its ideal D8h symmetry. Both B3LYP/6-31+G* calculations and EPR observation have shown that the COT moiety in the anion radical of 1,2-dicarbo-tert-butoxycyclooctatetraene exists in a pair of degenerate D4h alternating bond angle conformations (a b1g distortion). The rapid (k = 3 × 107 s-1) interconversion between the two identical conformations leads to specifically predicted line width alternation effects in the EPR spectrum. The COT ring system in the 1,2-dicarbomethoxycyclooctatetraene anion radical [(CH3OOC)2COT-•], on the other hand, has a ground state with alternating bond lengths. Since this b2g distorted (COT-•) system has a plane of symmetry that can be drawn through the molecule and between the two substituents, no line width alternation effects can take place. However, in this system, the B3LYP/6-31+G* calculations predict an energy difference between the b1g and b2g distorted COT-• ring systems of less tha...

The C−O and C−H bonds of 18-crown-6 are activated when 18-crown-6 is complexed with the potassium salt of the benzene anion radical. Evacuated glass bulbs containing the solid anion radical salt of potassium 18-crown-6 benzene anion radical were plunged into a bath at 320 °C, resulting in mini-explosions and generating a series of compounds including dioxane, 2-methyl-1,3-dioxolane, divinyl ether, hydrogen, methane, and 15-crown-5. Deuterium labeling studies proved that all of these compounds originated from the 18-crown-6. Further, these labeling studies were an aid in discerning the mechanism of the decomposition. Benzene, 1,4-cyclohexadiene, and cyclohexene were also generated. The last two originated from the reaction of the anion radical of benzene with hydrogen.

The solid dianion salt of 1,2-di-13C-cyclooctatetraene was synthesized in order to measure the first 13C−13C NMR coupling in an aromatic annulene other than benzene and to find out if this dianion will undergo high-temperature automerizations analogous to those previously observed in the benzene system. The solid potassium salt was heated to over 600 °C for 2 h, and although decomposition with H2 and CH4 evolution takes place, there is no observable scrambling of the 13C's. The positions of the 13C's were monitored via NMR, which necessitated a rather complete understanding of the NMR couplings for the cyclooctatetraene dianion system. Interestingly, the 1JCH and 1JCC couplings for the aromatic COT2- system of 145.9 and 55.8 Hz are all quite comparable to those recently reported for the 1,2-di-13C-benzene system (158.6 and 55.8 Hz, respectively).

The solid potassium salts of the nitrobenzene anion radical [K+C6H5NO2•-(solid)] and all three nitrotoluene anion radicals were generated via the potassium reduction of the nitroaromatic in liquid ...

The very reactive Rieke cadmium metal was allowed to react under vacuum with benzoquinone in tetrahydrofuran. This resulted in the formation of several different paramagnetic species whose EPR spectra prove them to have doublet multiplicities. The tetrahedral coordination sphere of each of these species consists of three THF molecules and an anion radical that is either asymmetrically coordinated or symmetrically coordinated to the metal dication. This latter species yields a 'IlCd hyperfine splitting of 6.86 G. The second anion radical lies outside this coordination sphere, and it can be either asymmetrically ion associated with or dissociated from the tetrahedral metal complex. All species have the general formula [Cd(CBH402'-)(~3]+,CsH402'or ([Cd(CsH402*-)(THF)31+ + C6H40;-}.

A series of electron transfer competition reactions between several isotopically different benzophenones was established in liquid ammonia. The resulting electron transfer (A .- +B=A+B .- ) equilibrium constants were determined via EPR studies and via the physical separation of the anion radical phase from the neutral molecule phase. This anion radical-neutral molecule separation leads to a partial separation of the isotopic isomers involved due to the deviation of the equilibrium constants from unity

The solid potassium salts of the nitrobenzene anion radical [K+C6H5NO2•-(solid)] and all three nitrotoluene anion radicals were generated via the potassium reduction of the nitroaromatic in liquid ...

EPR analysis shows that the anion radical of 2,6-dinitrotoluene (DNT) in liquid ammonia exists with the counterion (either K+ or Na+) associated with one of the two nitro groups. This tight association (−NO2•-M+) persists after solvent removal, and it renders the anion radical very susceptible to loss of metal nitrite. The slightest agitation of the solid potassium salt of DNT•- leads to detonation, and formation of KNO2 and polymer (in the solid phase) and CH4, HCN, H2, and N2O (in the gas phase). Trapping experiments suggest that the methane comes from carbenes, and it is suggested that the HCN comes from an anthranil radical intermediate. The potassium anion radical salts of 1,3-dinitrobenzene, 2,6-dinitrotoluene, 1,3,5-trinitrobenzene, and 2,4,6-trinitrotoluene all readily lose KNO2, and the ease of C−NO2•-M+ bond rupture increases with the degree of nitration. In the cases of the two trinitrated systems dissociation takes place immediately upon anion radical formation in liquid ammonia. This observat...

Alkali metal over-reduction of an electron acceptor in the presence of a hydrogen atom donor, in hexamethylphosphoramide (HMPA), results in a radical that is not simply the anion radical of the acceptor. This new species exhibits an enigmatic EPR pattern. Using 15N and 2H labeling studies, the "HMPA degradation product" was found to be the anion radical of N,N'-dimethyl-1,4-diazabutadiene. DFT calculations support this assignment and a mechanism for its formation.

Solutions of 1,4-bis(dihydroquininyl)-anthraquinone {(DHQ)2AQN} in either hexamethylphosphoramide (HMPA) or liquid ammonia undergo a photoinduced electron transfer from the solvent to the (DHQ)2AQN. The resulting anion radical {(DHQ)2AQN•-} yields coupling to the six (3 sets of 2 equivalent) protons on the anthraquinone moiety upon EPR analysis. The same anion radical can be generated via alkali metal reduction in tetrahydrofuran. Further exposure of the HMPA solution to visible light causes the anion radical to undergo a conformational change. The photorearranged product allows delocalization of spin into the γ proton on the sp3 hybridized alkoxy carbon. In NH3(liq) and THF, hydrogen bonding and ion association prevents this photorearrangement, respectively.

When a cold (200 K) THF solution of 1,6-heptadiyne is exposed to potassium tert-butoxide, in the presence of 18-crown-6, a green, EPR active solution is spontaneously formed. The intensity of the EPR signal can be augmented by exposure to alkali metal. Analysis of the EPR splitting pattern indicates that the signal originates from the anion radical of 7,14-di-trans-1,5- [14]annuldiyne. Allowing the green-colored solution to warm to ambient temperatures causes an immediate color change (to deep purple) and loss of the EPR activity. Reduced pressure distillation of the solution affords a colorless THF solution containing (spiro[2.6]nona-2,6,8-triene), which is only the second spirocyclopropene compound reported. The base condensation of the diyne is of a general nature as the same spirocyclopropenyl system is obtained from 1,6-heptadiyne, 1,7-octadiyne, and 1,8-nonadiyne. Laser irradiation (337 nm) of tungsten hexacarbonyl in the presence of the spirocyclopropenyl compound yields the stable organometallic: eta2-olefin pentacarbonyl complex.

Electron paramagnetic resonance spectroscopy has been used to discriminate between the R- and S-forms of the anion radical of camphorquinone. In a chiral solvent [SS- or RR-2,3-dimethoxy-1,4-bis(dimethylamino)butane saturated with sodium iodide], ion association between the semidione and Na+ takes place. PM3 calculations suggest that the complex relationship between the solvent, anion, and cation varies sufficiently with changes in the chiral nature of the solvent or anion radical to alter the appearance of the EPR signal allowing EPR chiral discrimination.

The one-electron reduction of neutral pi-stacked di- and trifluorenes (F-2 and F-3) in HMPA, where ion association is absent, results in the formation of anion radicals in which the odd electron resides predominantly on just one of the external fluorene moieties, as established by EPR spectroscopy. However, in the case of tetrafluorene, introduction of a single electron leads to a kinetically controlled anion radical F-4(int)*- in which the odd electron undergoes rapid exchange between two central fluorene rings, where the anionic charge is partially shielded from solvation due to the presence of external fluorene rings. On a time scale of minutes, anion radical F-4(int)*- converts to a thermodynamically stabilized anion radical F-4(ext)*-, with the electron exhibiting coupling from the protons on an external fluorene moiety. The charge and spin residing on an external moiety allow efficient solvation of the anionic charge. A similar fast exchange of a single electron (probably with the involvement of quantum mechanical tunneling) among three and four internal fluorene moieties is initially observed via EPR spectroscopy in the penta- and hexafluorene derivatives, F-5 and F-6, respectively.

A series of N-methylated polyarylurea oligomers have been reduced with potassium metal in HMPA. These reductions result in the transient formation of arylurea anion radicals, which undergo reductive elimination of the urea linkages. The aryl moieties appear in the products as the anion radicals of oligoaryl systems. The reaction is intramolecular, and the sequencing in the polyaryl anion radical remains the same as in the polyarylureas due to the urea-enforced pi-pi stacking interactions.

[reaction: see text] Low temperature (-100 degrees C) dehydrohalogenation of 1,2,5,6,9,10-hexabromocyclododecane (a common fire retardant) with potassium tert-butoxide in THF followed by one-electron reduction yields the anion radical of the di-trans form of [12]annulene. This system yields a well-resolved EPR signal that reveals that most of the spin density resides on one side (the planar side) of the anion radical. Five of the carbons in this [12]annulene system are twisted from the plane of the remaining seven carbons, and the rate of rearrangement between the degenerate conformations is on the EPR time scale (k = 10(6)-10(7) s(-1)). Warming of the solution results in the formation of a sigma-bond between the two internal carbons, loss of molecular hydrogen, and consequent generation of the anion radical of heptalene. Tractable quantities of neutral heptalene can be obtained via the reoxidation of this anion radical with iodine.

The anion radicals of alkoxy-substituted cyclooctatetraenes in hexamethylphosphoramide spontaneously dimerize to form the dianions of dialkoxy-[16]annulenes. The dianions reveal the expected high-field NMR resonance for the internal protons. After electron transfer, the EPR spectra of the corresponding anion radicals reveal that only the 1,5-dialkoxy systems are formed. Further, the measured proton and (13)C spin densities show that the odd electron resides in a molecular orbital with six hydrogens in "deep" nodal positions that completely hide them from EPR detection. This MO corresponds to the nonbonding (singly occupied) MO of higher energy after splitting of the degenerate nonbonding MOs by the two-electron-withdrawing substituents. The surprising electron-withdrawing nature of the alkoxy substituents is attributed to a rather strong mixing of the sigma and pi systems in [16]annulene.

Ninhydrin (the fingerprint developing agent) spontaneously dehydrates in liquid ammonia and in hexamethylphosphoramide (HMPA) to form indantrione, which has a sufficiently large solution electron affinity to extract an electron from the solvent (HMPA) to produce the indantrione anion radical. In liquid NH(3), the presence of trace amounts of amide ion causes the spontaneous formation of an anion radical condensation product, wherein the no. 2 carbon (originally a carbonyl carbon) becomes substituted with -NH(2) and -OH groups. In HMPA, the indantrione anion radical spontaneously forms condensation products with the HMPA to produce a variety of zwitterionic radicals, wherein the no. 2 carbon becomes directly attached to a nitrogen of the HMPA. The mechanisms for the formation of the zwitterionic paramagnetic condensation products are analogous to that observed in the reaction of ninhydrin with amino acids to yield Ruhemann's Purple, the contrast product in fingerprint development. The formation of anion and zwitterionic radical condensation products from ninhydrin and nitrogen-containing solvents may represent an example of a host of analogous polyketone-solvent reactions.

The solid anion radical salts resulting from the reductions of naphthalene, pyrene, perylene, benzo[k]fluoranthene, and biphenyl with lithium, cesium, and potassium metals were either pyrolyzed at 200-380 degrees C or irradiated with a pulsed frequency doubled Nd:YAG laser (532 nm wavelength). For both the pyrolytic and laser photolytic studies the only volatile products were hydrogen and methane. The hydrogen originated from the anionic polymerization of the anion radical. Evidence is presented that suggests that the methane results from a carbene intermediate, which in turn reacts with the H(2). Consistent with the H(2) formation, MALDS mass spectral analysis revealed the presence of dimers, trimers, and higher polymers of the polyaromatic hydrocarbon in the remaining nonvolatile products. There were considerably fewer low molecular weight oliomers produced via the laser photolysis than via the thermolysis.