A
quantum chemical investigation of the stability of compounds with identical
formulas was carried out on 23 classes of compounds made of C, N, P, O, S atoms
as core structures and halogens H, F, Cl, Br, I as substituents. All possible
structures were generated and investigated by quantum mechanical methods. The
prevalence of formula in which its <i>Z</i> configuration, <i>gauche</i>
conformation and meta isomer are the most stable forms is calculated and
discussed. Quantitative and qualitative models to explain the stability of the
23 classes of halogenated compounds were also proposed.<br>
A
quantum chemical investigation of the stability of compounds with identical
formulas was carried out on 23 classes of compounds made of C, N, P, O, S atoms
as core structures and halogens H, F, Cl, Br, I as substituents. All possible
structures were generated and investigated by quantum mechanical methods. The
prevalence of formula in which its <i>Z</i> configuration, <i>gauche</i>
conformation and meta isomer are the most stable forms is calculated and
discussed. Quantitative and qualitative models to explain the stability of the
23 classes of halogenated compounds were also proposed.<br>
A quantum chemical
investigation of the stability of compounds with identical formulas was carried
out on 23 classes of halogenated compounds made of H, F, Cl, Br, I, C, N, P, O
and S atoms. All possible structures were generated by combinatorial
approach and studied by statistical methods. The prevalence of formula in which
its <i>Z</i> configuration, <i>gauche</i> conformation and meta isomer are the
most stable forms is calculated and discussed. Quantitative and qualitative
models to explain the stability of the 23 classes of halogenated compounds were
also proposed.<br>
<div>A quantum chemical investigation of the stability of compounds with identical formulas was carried out on 23 classes of halogenated compounds made of H, F, Cl, Br, I, C, N, P, O and S atoms. The prevalence of formula in which its Z configuration, gauche conformation and meta isomer are the most stable forms is calculated and discussed. The prevalence data shows that in compounds made of carbon backbones, the electronic effect is weaker than the steric effect. The electronic factor is more important as the backbone atoms are replaced with atoms on the right and upper part of the periodic table.</div>
<div>A quantum chemical investigation of the stability of compounds with identical formulas was carried out on 23 classes of halogenated compounds made of H, F, Cl, Br, I, C, N, P, O and S atoms. The prevalence of formula in which its Z configuration, gauche conformation and meta isomer are the most stable forms is calculated and discussed. The prevalence data shows that in compounds made of carbon backbones, the electronic effect is weaker than the steric effect. The electronic factor is more important as the backbone atoms are replaced with atoms on the right and upper part of the periodic table.</div>
Many-electron wavepacket dynamics based on time-dependent configuration interaction (TDCI) is a numerically rigorous approach to quantitatively model electron-transfer across molecular junctions. TDCI simulations of cyanobenzene thiolates---para- and meta-linked to an acceptor gold atom---show donor states conjugating with the benzene $\pi$-network to allow better through-molecule electron migration in the para isomer compared to the meta counterpart. For dynamics involving non-conjugating states, we find electron-injection to stem exclusively from distance-dependent non-resonant quantum mechanical tunneling, in which case the meta isomer exhibits better dynamics. Computed trend in donor-to-acceptor net-electron transfer through differently linked azulene bridges agrees with the trend seen in low-bias conductivity measurements. Disruption of $\pi$-conjugation has been shown to be the cause of diminished electron-injection through the 1,3-azulene, a pathological case for graph-based diagnosis of destructive quantum interference. Furthermore, we demonstrate quantum interference of many-electron wavefunctions to drive para- vs. meta- selectivity in the coherent evolution of superposed $\pi$(CN)- and $\sigma$(NC-C)-type wavepackets. Analyses reveal that in the para-linked benzene, $\sigma$ and $\pi$ MOs localized at the donor terminal are in-phase leading to constructive interference of electron density distribution while phase-flip of one of the MOs in the meta isomer results in destructive interference. These findings suggest that a priori detection of orbital phase-flip and quantum coherence conditions can aid in molecular device design strategies.
Many-electron wavepacket dynamics based on time-dependent configuration interaction (TDCI) is a numerically rigorous approach to quantitatively model electron-transfer across molecular junctions. TDCI simulations of cyanobenzene thiolates---para- and meta-linked to an acceptor gold atom---show donor states <i>conjugating</i> with the benzene $\pi$-network to allow better through-molecule electron migration in the para isomer compared to the meta counterpart. For dynamics involving <i>non-conjugating</i> states, we find electron-injection to stem exclusively from distance-dependent non-resonant quantum mechanical tunneling, in which case the meta isomer exhibits better dynamics. Computed trend in donor-to-acceptor net-electron transfer through differently linked azulene bridges agrees with the trend seen in low-bias conductivity measurements. Disruption of $\pi$-conjugation has been shown to be the cause of diminished electron-injection through the 1,3-azulene, a pathological case for graph-based diagnosis of destructive quantum interference. Furthermore, we demonstrate quantum interference of many-electron wavefunctions to drive para- vs. meta- selectivity in the coherent evolution of superposed $\pi$(CN)- and $\sigma$(NC-C)-type wavepackets. Analyses reveal that in the para-linked benzene, $\sigma$ and $\pi$ MOs localized at the donor terminal are <i>in-phase</i> leading to constructive interference of electron density distribution while phase-flip of one of the MOs in the meta isomer results in destructive interference. These findings suggest that <i>a priori</i> detection of orbital phase-flip and quantum coherence conditions can aid in molecular device design strategies.
Deoxygenation of the lignin model compound resorcinol was investigated using VUV synchrotron radiation: Formation of two reactive ketenes and decarboxylation are the dominating pathways, much different from the other two benzenediol isomers.
In our effort to prepare [m.n]cyclophanes carrying functional groups in their molecular bridges, the thiacyclophanes 14, 19, 20, and 21 have been prepared by simple routes from the pseudo-gem dibromide 10a and the corresponding bis-thiol 10b. The triply-bridged bis-thia-cyclophanes 14, and 19-21 were characterized by their spectroscopic data as well as by X-ray structural analyses. The meta-isomer 20 was oxidized to the bis-sulfone 23, which on flash vacuum pyrolysis (FVP) yielded a product mixture presumably containing the hydrocarbon 26 with a cleaved molecular bridge. Subjecting 23 to Ramberg-Bäcklund conditions (CCl4, NaOH, phase transfer catalysis) provided the chloride 24 in poor yield (9%), a [2.2]paracyclophane in which the new molecular bridge is fully conjugated.
An attempt has been made in in-situ preparation and application of two isomers (para and meta) of aminophenyl-b-sulphatoethyl sulphone reagents (PABSES and MABSES) with three dichlorotriazinyldyes i.e. CI Reactive Orange 86, CI Reactive Red 11 and CI Reactive Blue 168 to generate mixed hetero bifunctional dyes in dye bath. Dyeing results when compared with similar targeted type of commerciallyavailable Sumifix Supra dyes were found not up to the mark. Build up properties of all in situ prepared dyes were lower except for few light depth of shades as compared to preformed commercial Sumifix Supradyes. This could be because of inefficient condensation of dichlorotriazinyl dyes with the aminophenyl- b-sulphatoethyl sulphone. However, meta isomer of aminophenyl-b-sulphatoethyl sulphone appeared tobe more effective than the para isomer.
Steric effects vs electron delocalization: a new look into stability of diastereomers, conformers and constitutional Isomers