Relative Stability Of Species Research Articles

ChemInform Abstract: Influence of Sulfur for Oxygen Substitution in the Solvolytic Reactions of Chloroformate Esters and Related Compounds

AbstractReview: 88 refs.

Influence of sulfur for oxygen substitution in the solvolytic reactions of chloroformate esters and related compounds.

The replacement of oxygen within a chloroformate ester (ROCOCl) by sulfur can lead to a chlorothioformate (RSCOCl), a chlorothionoformate (ROCSCl), or a chlorodithioformate (RSCSCl). Phenyl chloroformate (PhOCOCl) reacts over the full range of solvents usually included in Grunwald-Winstein equation studies of solvolysis by an addition-elimination (A-E) pathway. At the other extreme, phenyl chlorodithioformate (PhSCSCl) reacts across the range by an ionization pathway. The phenyl chlorothioformate (PhSCOCl) and phenyl chlorothionoformate (PhOCSCl) react at remarkably similar rates in a given solvent and there is a dichotomy of behavior with the A-E pathway favored in solvents such as ethanol-water and the ionization mechanism favored in aqueous solvents rich in fluoroalcohol. Alkyl esters behave similarly but with increased tendency to ionization as the alkyl group goes from 1° to 2° to 3°. N,N-Disubstituted carbamoyl halides favor the ionization pathway as do also the considerably faster reacting thiocarbamoyl chlorides. The tendency towards ionization increases as, within the three contributing structures of the resonance hybrid for the formed cation, the atoms carrying positive charge (other than the central carbon) change from oxygen to sulfur to nitrogen, consistent with the relative stabilities of species with positive charge on these atoms.

Analysing links between biogeography, niche stability and speciation: the impact of complex feedbacks on macroevolutionary patterns

Understanding the processes that control speciation is critical to any modern macroevolutionary synthesis. A variety of theoretical constructs have been proposed to explain various differential speciation patterns observed in the fossil record, such as higher rates of speciation among stenotopic vs. eurytopic species. Most of these explanations, however, rely on only one or two explanatory variables and may be overly simplistic. Developing a more complete understanding of speciation processes requires a broader synthesis of multiple explanatory factors including the role of external factors such as climate and plate tectonics, impact of ecosystem‐level processes, relative niche breadth and relative stability of species’ niches during environmental change (biotic and abiotic). This study explores the relationship between biogeography, ecological niches and speciation in a series of case studies focusing on the Late Ordovician and Late Devonian shallow marine brachiopods and bivalves and Neogene horses of North America.

Concerted Asynchronous Proton Transfer in H-Bonding Relay Model: An Implication of Green Fluorescent Protein

was obtained by CIS method. Based on the relative stabilities ofspecies and the energy barriers for the proton transfer, it was found that proton transfer could take place bothunder the ground state and the first excited state. As determined by the proton motions along the reactioncoordinate, both the ground state proton transfer (GSPT) and the excited state proton transfer (ESPT) areconsidered as a concerted and asynchronous process. Key Words : Green fluorescent protein, Proton transfer, Concerted, Asynchronous, TheoreticalIntroductionThe transportation of a proton from one atom to another inthe electronic ground and excited states of molecules is afundamentally important process that plays a crucial role inlots of reactions, especially chemical and biological pro-cesses.