Electron affinity, acetylene

Ervin et al. [27] have determined the electron affinity of the acetylide radical, HC = C-, to be equal to 2.969 + 0.010 eV and the enthalpy of the acid dissociation of acetylene in the gas phase to be equal to 377.8 + 0.6 Kcal mol Use these data, together with the ionization potential of the hydrogen atom, 13.595 eV, to calculate the enthalpy for the dissociation of the CH bond in acetylene. The ionization potentials are properly applied at 0 K, but a good approximation is to assume that they are equal to enthalpy changes at 298.15 K, the temperature at which the enthalpy of the acid dissociation was measured. 

Quinones, Semiquinones, and Catechols. All molecules with unsaturated bonds (olefins, acetylenes, aromatics, carbonyls, quinones, etc.) have a degree of electrophilicity and electron affinity. Within a class, the extent of conjugation... 

Ethynyi Groups According to Ref. [77], acetylene fragments introduced into polyimides, e.g., 2,2 -diethynylbenzidine, DEB, have TT-electron affinity for aromatic compounds. It can be seen from the data presented in Table 9.12 that the increase in the content of DEB component results in an increase in the separation factor of the benzene/cyclohexane mixture. This is probably caused not only by the growth of the diffusion component /8d (resulting from thermal cross-linking through the unsaturated bonds) but also by enhancement of the sorption component /Ss-... 

Electron transmission spectroscopy of 3 and 4, which measures gas-phase electron affinities, reveals an even larger splitting (ca. 1.6 eV) of the nonbonding orbitals in these pericyclynes [9]. The lowest unoccupied molecular orbitals (LUMOs) are stabilized by 0.4-0.7 eV relative to the LUMO of acetylene. 

Acetylene, apparently, can be reduced by nitrogenase at high- and low-affinity sites either in vitro (Davis et al., 1975) or in vivo (Walker and Yates, 1978). Furthermore, preexposure to acetylene enhances the subsequent rate of acetylene reduction I /i vivo (David and Fay, 1977 David e/ al., 1978 Apte et al., 1978 Walker and Yates, 1978b) in the presence of chloramphenicol, which inhibits protein synthesis (Apte et al., 1978). It is likely, therefore, to be an acetylene-induced conformation change in the nitrogenase, but a possible effect on ATP synthesis or electron transfer to nitrogenase cannot be ruled out at this stage. 

The cation-TT interaction involves binding of a cation to Ji-electrons (e.g., benzene, acetylene). Early mass spectrometry and ion cyclotron resonance studies have established that alkali-metal cations (e.g., Na+) bind strongly to simple aromatics. Later, Deakyne, and Meolner showed that organic ions (e.g., alkylammoniums) display affinities for aromatics. Moreover, extensive work by Dougherty and CO workers has established models of the cation- n- interaction that have been successfully demonstrated in a variety of synthetic receptors. ... 

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