Browsing by Subject "Molecular structure"

Now showing 1 - 3 of 3
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    Accurate ring strain energies of unsaturated three-membered heterocycles with one group 13–16 element
    (American Chemical Society, 2022-05-02) Rey Planells, Alicia; Espinosa Ferao, Arturo; Química Orgánica
    High-quality ring strain energy (RSE) data for 1H-unsaturated (CH)2X parent rings, where X is a group 13–16 element, are reported in addition to the 2H-isomers of the pnictogenirene rings. RSE data are obtained from appropriate homosdesmotic reactions and calculated at the DLPNO-CCSD(T)/def2-TZVPP//B3LYP-D3/def2-TZVP(ecp) level. 1H-Tallirene and 1H-plumbirene have unique donor–acceptor structures between an acetylene π(CC) orbital and an empty p orbital of a metallylene subunit (a Dewar–Chatt–Duncanson description) and therefore cannot be described as proper rings but as pseudocyclic structures. Also, 1H-indirene and 1H-oxirene lack ring critical points and constitute borderline cases of pseudorings. 1H-Unsaturated rings exhibit enhanced RSE compared to their saturated homologues. The mechanism of ring strain relaxation by increasing the s character in the lone pair (LP) of group 15–16 elements is remarkable and increases on descending the groups. Furthermore, RSE is affected by the aromatic character of group 13 rings and certain aromatic or antiaromatic character in group 14 or 15–16 rings, respectively, which tend to vanish on descending the group as shown by NICS(1) values. 2H-Unsaturated rings were found only for group 15 elements (although only 2H-azirine shows a proper cyclic structure) and displayed lower RSE (higher stability) than the corresponding 1H-isomers.
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    Removal of different dye solutions: A comparison study using a polyamide nf membrane
    (MDPI, 2020-12-10) Hidalgo, A.M.; León, G.; Gómez, M.; Murcia, M.D.; Gómez, E.; Macario, J.A.; Ingeniería Química
    The removal of organic dyes in aquatic media is, nowadays, a very pressing environmental problem. These dyes usually come from industries, such as textiles, food, and pharmaceuticals, among others, and their harm is produced by preventing the penetration of solar radiation in the aquatic medium, which leads to a great reduction in the process of photosynthesis, therefore damaging the aquatic ecosystems. The feasibility of implementing a process of nanofiltration in the purification treatment of an aqueous stream with small size dyes has been studied. Six dyes were chosen: Acid Brown-83, Allura Red, Basic Fuchsin, Crystal Violet, Methyl Orange and Sunset Yellow, with similar molecular volume (from 250 to 380 Å). The nanofiltration membrane NF99 was selected. Five of these molecules with different sizes, shapes and charges were employed in order to study the behavior of the membrane for two system characteristic parameters: permeate flux and rejection coefficient. Furthermore, a microscopy study and a behavior analysis of the membrane were carried out after using the largest molecule. Finally, the Spiegler–Kedem–Katchalsky model was applied to simulate the behavior of the membrane on the elimination of this group of dyes.
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    Ring strain energies of three-membered homoatomic inorganic rings El3 and diheterotetreliranes El2Tt (Tt = C, Si, Ge): accurate versus additive approaches
    (American Chemical Society, 2022-09-05) Rey Planells, Alicia; Espinosa Ferao, Arturo; Química Orgánica
    Accurate ring strain energies (RSEs) for three-membered symmetric inorganic rings El3 and organic dihetero-monocycles El2C and their silicon El2Si and germanium El2Ge analogues have been computed for group 14–16 “El” heteroatoms using appropriate homodesmotic reactions and calculated at the DLPNO-CCSD-(T)/def2-TZVPP//B3LYP-D4/def2-TZVP(ecp) level. Rings containing triels and Sn/Pb heteroatoms are studied as exceptions to the RSE calculation as they either do not constitute genuine rings or cannot use the general homodesmotic reaction scheme due to uncompensated interactions. Some remarkable concepts already related to the RSE such as aromaticity or strain relaxation by increasing the s-character in the lone pair (LP) of the group 15–16 elements are analyzed extensively. An appealing alternative procedure for the rapid estimation of RSEs using additive rules, based on contributions of ring atoms or endocyclic bonds, is disclosed.