RESUMEN
In the title compound, C(18)H(13)ClFN(3)O(2), the pyrrolidine ring adopts an envelope conformation and the planar part is rotated by 4.3â (6)° from the plane of the benzene ring and is almost perperdicular both to the diazo-acetyl unit [dihedral angle = 78.93â (7)°] and the phenyl ring [dihedral angle = 86.07â (7)°]. In the crystal, mol-ecules are linked into a three-dimensional framework by C-Hâ¯O inter-actions. The mol-ecular conformation is stabilized by an intra-molecular C-Hâ¯O hydrogen bond.
RESUMEN
In the title compound, C(23)H(25)NO(5), the lactam ring adopts an envelope conformation and both eth-oxy-carbonyl side chains show an s-cis conformation: one is nearly planar, the dihedral angle between CO(2) and OCH(2)CH(3) groups being 7.95â (14)° and the other is almost orthogonal, the C-O-C-C torsion angle being 85.33â (9)°. Dimers related by inversion symmetry are stabilized by C-Hâ¯O hydrogen bonds. The crystal structure is consolidated by weak intermolecular C-Hâ¯O inter-actions. Weak intra-molecular inter-actions of the same kind also occur.
RESUMEN
The title compounds, C20H20FNO6 and C20H19Cl2NO6, respectively, may exhibit bioactivity. In these compounds, the pyrrolidine ring adopts a conformation intermediate between envelope and half-chair. Only one of the two ethoxycarbonyl side chains is nearly planar. Centrosymmetric pairs are formed, and the crystal structure is stabilized by weak C-H.O hydrogen bonds and van der Waals interactions.
RESUMEN
The photodegradation of pesticides is reviewed, with particular reference to the studies that describe the mechanisms of the processes involved, the nature of reactive intermediates and final products. Potential use of photochemical processes in advanced oxidation methods for water treatment is also discussed. Processes considered include direct photolysis leading to homolysis or heterolysis of the pesticide, photosensitized photodegradation by singlet oxygen and a variety of metal complexes, photolysis in heterogeneous media and degradation by reaction with intermediates generated by photolytic or radiolytic means.
Asunto(s)
Plaguicidas/química , Fotólisis , Animales , Humanos , LuzRESUMEN
One of the possible ways of intracellular oxidation of peptides is via the formation of the corresponding (N-X)-dipeptides, that then undergo base-promoted elimination to yield intermediate 2-[N-alkyl-N-(2-N-alkylimino-2-alkylethanoyl)amino]-2,2-dialkylethanoic acids, which subsequently hydrolyze. Such an elimination process is general-base catalyzed, with Brønsted beta values ranging from 0.26 to 0.31, which suggests an essentially constant degree of proton transfer at the TS. For (N-X)-dipeptides, the ratio k(N-Br)/k(N-Cl) ranges from 2.5 to 15, suggesting a structural dependence of the degree of N-X bond breaking at the TS. The values of beta and k(N-Br)/k(N-Cl) support a concerted asynchronous A(xh)D(H)D(N) mechanism, its TS changing from reactant-like to slightly nitrenium-like depending on the structure of the starting dipeptide. As a consequence of the antiperiplanarity requirements of the reaction, the steric interaction between the leaving group and the substituent on the C bearing the H to be eliminated controls the reaction rate. Such steric interaction is rather important, as indicated by the steric crossed-interaction coefficient (p(ssy') = 0.33). Semiempirical calculations show that bulky substituents in the vicinity of the reaction center imply additional energy requirements for the system to achieve the antiperiplanarity needed at the TS for the reaction to proceed. From the observations reported it follows that (N-X)-dipeptides lose their oxidizing power more readily than analogous (N-X)-amino acids or (N-X)-amines, opening a possible pathway to lessen intracellular halogen-based oxidative stress.