A combination of experiment and theory provides insight into the structure and rearrangements of various C3H2 isomers. Photolysis of [13C]diazopropynes 6a−c under matrix isolation conditions affords C3H2 isomers containing a single 13C-label. With the aid of computed vibrational frequencies and intensities (CCSD(T)/cc-pVTZ), the seven 13C-isotopomers of triplet propynylidene 1a,b, singlet propadienylidene 2a−c, and singlet cyclopropenylidene 3a,b are readily distinguished by IR spectroscopy. Monitoring the distribution of the 13C-label during photolysis at either λ = 313 ± 10 nm or λ > 444 nm reveals the involvement of two photochemical automerization processes. At λ = 313 ± 10 nm, triplet propynylidene and singlet cyclopropenylidene photoequilibrate. The interconversion does not occur by a simple ring closure/ring opening mechanism, as hydrogen migration accompanies the interconversion. At λ > 444 nm, H2CC13C:  (2b) and H2C13CC:  (2c) rapidly equilibrate. Various lines of evidence suggest that the equilibration occurs through a cyclopropyne transition state. Computational results confirm that the planar isomer of singlet cyclopropyne (4a, C 2 v ) is the transition state for the interconversion of 2b and 2c. Unexpectedly, the calculations predict that the isomer of this compound containing a tetrahedral carbon atom (4b, C 2 v ) lies ca. 7 kcal/mol higher in energy than the planar form.

We have prepared ionic liquids by mixing either iron(II) chloride or iron(III) chloride with 1-butyl-3-methylimidazolium chloride (BMIC). Iron(II) chloride forms ionic liquids from a mole ratio of 1 FeCl(2)/3 BMIC to almost 1 FeCl(2)/1 BMIC. Both Raman scattering and ab initio calculations indicate that FeCl(4)(2-) is the predominant iron-containing species in these liquids. Iron(III) chloride forms ionic liquids from a mole ratio of 1 FeCl(3)/1.9 BMIC to 1.7 FeCl(3)/1 BMIC. When BMIC is in excess, Raman scattering indicates the presence of FeCl(4-). When FeCl(3) is in excess, Fe(2)Cl(7-) begins to appear and the amount of Fe(2)Cl(7-) increases with increasing amounts of FeCl(3). Ionic liquids were also prepared from a mixture of FeCl(2) and FeCl(3) and are discussed. Finally, we have used both Hartree-Fock and density functional theory methods to compute the optimized structures and vibrational spectra for these species. An analysis of the results using an all-electron basis set, 6-31G, as well as two different effective core potential basis sets, LANL2DZ and CEP-31G is presented.

The geometries and force fields of phenylcarbene (PC) and cycloheptatrienylidene (CHT) in their singlet and triplet electronic states as well as of cycloheptatetraene (CHTE) and bicyclo[4.1.0]heptatriene (BCT) and the transition states for the formation and decay of the latter were evaluated by various methods. Relative single point energies were calculated at the CCSD(T)/cc-pVDZ//BLYP/6-31G* level. Finally, the effects of extending the basis set to triple-ζ quality were estimated by (R)MP2 calculations and carried over proportionally to CCSD(T). These calculations show that CHTE which has a strongly distorted allenic structure is the most stable species on that part of the C(CH)6 surface which was examined in the present study, followed by planar 3PC. The strained BCT is found to be nearly degenerate in energy with 1PC, but the high activation energy for its formation from 1PC together with the low activation energy for ring-opening to CHTE suggests that this species cannot persist under the experimental conditions employed for production of CHTE. In analogy to the case of cyclopentadienylidene, CHT exists in the form of a closed shell singlet (1A1) and two related pairs of open shell singlet and triplet states (1,3A2 and 1,3B1) which correspond to the Jahn−Teller distorted structures of the cycloheptatrienyl radical. The relative energies and the nature of the different CHT stationary points depend on the method of calculation, but it appears that the decrease in electron repulsion lowers the 1A2 state slightly below the 1A1 state so that the open shell species serves as a planar transition state for enantiomerization of CHTE with an estimated activation energy of ∼20 kcal/mol. The two triplets are very close in energy with the higher lying being either a transition state or a shallow minimum. The 1B1 state is an excited state of the open-shell singlet. The calculated IR spectra of the three most stable isomers were compared to those published previously by Chapman et al. whereby the assignment of the photoproduct of UV photolysis of phenyldiazomethane to CHTE was confirmed. A full study of the force fields of PC and CHTE is under way.

Trenbolone acetate (TBA) is a high-value steroidal growth promoter often administered to beef cattle, whose metabolites are potent endocrine-disrupting compounds. We performed laboratory and field phototransformation experiments to assess the fate of TBA metabolites and their photoproducts. Unexpectedly, we observed that the rapid photohydration of TBA metabolites is reversible under conditions representative of those in surface waters (pH 7, 25°C). This product-to-parent reversion mechanism results in diurnal cycling and substantial regeneration of TBA metabolites at rates that are strongly temperature- and pH-dependent. Photoproducts can also react to produce structural analogs of TBA metabolites. These reactions also occur in structurally similar steroids, including human pharmaceuticals, which suggests that predictive fate models and regulatory risk assessment paradigms must account for transformation products of high-risk environmental contaminants such as endocrine-disrupting steroids.