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Boosted molecular mobility during common chemical reactions

Science

During a chemical reaction, the reorganization of solvent molecules not directly in contact with reactants and products is normally viewed as a simple diffusion response. Wang et al. studied molecular diffusion in six common reactions—including the copper-catalyzed click reaction and the Diels-Alder reaction—with pulsed-field gradient nuclear magnetic resonance. They observed a boost in mobility relative to Brownian diffusion that was stronger for the catalyzed reactions that were studied. The mobilities for the click reaction were verified with a microfluidic gradient method. They argue that energy release produces transient translational motion of reacting centers that mechanically perturbs solvent molecules. Science , this issue p. [537][1] Mobility of reactants and nearby solvent is more rapid than Brownian diffusion during several common chemical reactions when the energy release rate exceeds a threshold. Screening a family of 15 organic chemical reactions, we demonstrate the largest boost for catalyzed bimolecular reactions, click chemistry, ring-opening metathesis polymerization, and Sonogashira coupling. Boosted diffusion is also observed but to lesser extent for the uncatalyzed Diels-Alder reaction, but not for substitution reactions SN1 and SN2 within instrumental resolution. Diffusion coefficient increases as measured by pulsed-field gradient nuclear magnetic resonance, whereas in microfluidics experiments, molecules in reaction gradients migrate “uphill” in the direction of lesser diffusivity. This microscopic consumption of energy by chemical reactions transduced into mechanical motion presents a form of active matter. [1]: /lookup/doi/10.1126/science.aba8425


Little boy has adorably sweary reaction to trying out VR

Mashable

If you want to guarantee yourself some instant comedy, just pop a VR headset on your child and observe their startled reaction. The 3-year-old British boy in the clip above, according to the YouTube description, is watching a video of the solar system -- which makes it even more confusing when he suddenly blurts out "Oh, you little bitch!" halfway through the video. Ever wanted to make your own Big Kahuna burger? A toddler causes chaos in a CNN studio because that's what toddlers do


An enantioconvergent halogenophilic nucleophilic substitution (SN2X) reaction

Science

Biomolecular substitution reactions are widely applied to compounds with carbon-halogen bonds. Typically, an incoming reactive group will attack the carbon from behind its bond with the halogen, causing the halogen to depart in the opposite direction. Zhang et al. now present an asymmetric catalytic substitution reaction that flips the script with an attack on the halogen from the front. Specifically, nitrogen and sulfur nucleophiles stripped bromine from a variety of carbon centers activated by electron-withdrawing groups. A chiral cationic catalyst then directed the carbon fragment back to form a carbon-sulfur or carbon-nitrogen bond enantioselectively.


[Perspective] Rethinking the SN2 reaction

Science

The SN2 nucleophilic substitution reaction, X RY XR Y, is a paradigm reaction in organic chemistry (1). The modern understanding of the SN2 reaction mechanism is based on work of Hughes and Ingold (2), who proposed that the nucleophile (X) approaches the carbon atom that bears the leaving group (Y). As a result, the bond between the carbon atom and the leaving group becomes weakened. As this bond breaks and a new bond forms between the nucleophile and the carbon atom, the configuration of the carbon atom is inverted. Analyses of gas-phase reaction rates led to the suggestion of a potential energy surface (PES) with two wells connected by a central barrier transition state (3).


On Facebook, love reactions triumph over hate

Engadget

Ever since Facebook introduced reactions a year ago, there's been a lingering question: which reactions rule? At last, we know... although you can probably guess the answer. Facebook tells Select All that "love" dominated the 300 billion reactions from the past year -- more than half of them were hearts. That's not completely surprising (how many people do you know who use it for just about everything positive?), Also, you might be surprised at where reactions ruled.