, 2552 (1984). Quantitative measures of electron detachment from anthracene and various meso-substituted derivatives (D) are examined in the gas phase and in solution. The photoelectron spectra show well-resolved bands for El corresponding to the first ionization (i.e., D -+ Df + e) from a T-molecular orbital (HOMO) with maximum electron density at the 9,10-positions. The same series of anthracenes form 1: 1 electron donor-acceptor complexes with tetracyanoethylene [D,TCNE], which exhibit distinctive colors associated with charge transfer transitions hvcT to the ion pair [Df,TCNE7]. These measures of the gas phase energetics of electron transfer from the anthracenes are compared with their standard oxidation potentials E:, determined from the reversible cyclic voltammograms in methylene chloride and trifluoroacetic acid solutions. Although there are direct, linear free energy relationships between E l and hum as well as E l and E:,, the best correlation is observed between E:, and hvCT. The validity of the latter is discussed in terms of offsetting effects arising from differences in solvation energy and steric effects attendant upon 9,10-substitution in anthracenes. [Traduit par le journal]

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Electron donor-acceptor (EDA) complexes have been observed experimentally3 and have been proposed as intermediates in many types of chemical reactions.4 56Among the earliest and most important examples are the 1:1 EDA complexes of various dienes and dienophiles involved in the Diels-Alder reaction,5,6 Indeed, theoretical studies have delineated the importance of chargetransfer (CT) interactions in thermal [4 + 2] as well as [2 + 2] cycloadditions.7 Experimental support for such formulations is found in the observation of a direct relationship between the second-order rate constant (log k) for the Diels-Alder cycloaddition and the CT transition energy {hvcf) for the EDA complexes of various anthracenes with tetracyanoethylene.8 9"10The EDA complex consisting of either 9-cyanoanthracene (CNA) or indene (IN) with tetracyanoethylene (TCNE) is ideally (1) Bell Laboratories.

135as primary reaction products. VOC2H4+ then reacts rapidly to form VOC4H6+ and VOC4H8+. The VOC4H6+ ion has a VO+-butadiene structure, while the VOC4Hs+ ion is a bis(ethene) species, as is shown by the CID spectra of the two species. VOC4H6+ regenerates VO+ as the primary CID product, while VOC4H8+ produces predominately VOC2H4+ at low CID energies and VO+ at high energies. With cyclopentane, both single and double dehydrogenations are seen with VO' , while V+ produces only the double dehydrogenation product. The product ions formed with VO+ do react further to form VOCIOHI2+, the bis-(cyclopentadiene) product, and only a trace of VOCloHlo+, while the V+ products react to produce exclusively the bis(cyc1opentadienyl) product. Cyclohexane undergoes one, two, and three dehydrogenations with VO+, while V+ induces a minimum of two. Finally, VO+ produces, again, products corresponding to one, two, and three dehydrogenations with methylcyclohexane, in addition to formation of VOC6H6+, while V+ forms only VC7Hs+ and VC&+. None of the product ions from vo+ react further with cyclohexane or methylcyclohexane, while secondary reactions are observed with V+, again suggesting that the presence of the oxygen ligand reduces the number of coordination sites, preventing further interactions. ConclusionsThe V+ ion reacts with hydrocarbons primarily by insertion into C-H bonds inducing dehydrogenation. In contrast to some of the later first-row transition-metal ions, such as Fe' , Co' , and Ni+,2b formation of secondary reaction products occurs with all of the hydrocarbons studied save for the largest linear alkanes.Addition of an oxide ligand to V+, producing VO', does not greatly change the chemistry observed. VO+ does react somewhat slower than V+ and is not as effective at dehydrogenating alkanes. In cases where coordinative saturation may influence reactivity, such as formation of secondary products, an effect is seen. In contrast to FeO' ," the oxide ligand does not appear to be involved in the reactions of VO+, since it is never lost in the course of reaction, and collision-induced dissociation of product ions containing VO+ always results in reformation of VO+ by loss of other ligands. This effect is undoubtedly due to the strong V+-0 bond. Abstract: Excitation within the charge-transfer (CT) band of the electron donor-acceptor or EDA complexes of tetranitromethane (TNM) with a series of 9-substituted and 9,lO-disubstituted anthracenes (An) leads to photochemistry in high quantum yields (a -I). The combined use of time-resolved picosecond spectroscopy, product isolation, and structure elucidation allows for the detailed mapping of the temporal evolution of the CT excited state to the photoproduct I via a series of discrete reactive intermediates. Thus electron transfer within the EDA complex occurs effectively (<25 ps) upon CT photoexcitation to form simultaneously An+. and TNM-a. The latter is not observed directly owing to its spontaneous fragmentation to C(N02)3and NO2 within I O ps. The geminate ionic intermediates A...