Synthesis and Blending of Two Poly(ethylene-co-vinyl alcohol) Polymers with Mixed 1,2-Diol Stereochemistry

Parallel pathways for the postpolymerization modification of double bonds in a polycyclooctene (PCOE) backbone generate vicinal 1,2-diol-containing polymers with mixed but opposite stereochemistry, depending on the trans:cis ratio of the C═C in PCOE. Beginning from the same batch of PCOE, epoxidation and subsequent ring-opening with sulfuric acid and water produce a polymer with the majority erythro diols, whereas an osmium-catalyzed dihydroxylation results in diols in the majority threo orientations. These postpolymerization modification approaches enable access to previously unexplored polymers with a mixture of erythro and threo diols, offering tunable diol stereochemistry to tailor material properties. The majority erythro diols lead to hexagonal crystallites with higher melting temperatures and overall crystallinity when compared to the majority threo diols that form monoclinic crystallites. When blended, the two diastereomers phase separate as evidenced by distinct melting endotherms and crystal structures corresponding to the two component polymers, suggesting a route to tune the barrier or mechanical properties. This investigation synthesized polymers with mixed stereochemical diols and elucidated the thermal and morphological properties of regioregular linear poly(ethylene-co-vinyl alcohols) and their blends.

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Quantification of the H-Bond-Donating Ability of Trifluoromethyl Ketone Hydrates Using a Colorimetric Sensor

Trifluoromethyl ketones (TFMKs) readily form stable hydrates and hemiketals in solution, allowing them to interact with biomolecules as hydrogen-bond donors. This interaction is governed by both the h...

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UV Photodissociation Dynamics of Organic Hydroperoxides: Experiment and Theory

The UV photodissociation dynamics of three organic hydroperoxides (ROOH, R = tert-butyl, cyclopentyl, and cyclohexyl) are examined experimentally at 282 nm utilizing velocity map imaging of the OH X2Π3/2 (v″ = 0, J″) products. The three systems have similar O–O bond dissociation energies based on W1BD calculations and thus similar energy release to products. In each case, the experimental total kinetic energy release (TKER) distributions are bimodal, composed of narrow low and broad high TKER components extending over the available energy. The associated angular distributions of the OH X2Π products are isotropic, differing dramatically from those predicted for direct photodissociation. Complementary theoretical calculations map the relaxed potential energy profile for each ROOH along the steeply repulsive excited state (S1) potential leading to RO + OH products. Low CCOO torsional barriers predicted along the ROOH dissociation pathway enable the OH products to recoil in many different directions, yielding isotropic angular distributions. Simple models of photodissociation suggest that the low TKER component arises from internal conversion to the ground state (S0) potential, leading to a common RO + OH product asymptote. A simple impulsive model for dissociation captures some aspects of the high TKER component but neglects significant geometric changes in the alkyl substituent from ROOH to the RO product. This study provides new insight into the solar photolysis of organic hydroperoxides and the regeneration of OH radicals in atmospheric oxidation cycles.

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Cross-Electrophile Coupling to Form Sterically Hindered C(sp2)–C(sp3) Bonds: Ni and Co Afford Complementary Reactivity

The formation of sterically hindered C(sp2)–C(sp3) bonds could be a useful synthetic tool but has been understudied in cross-electrophile coupling. Here, we report two methods that couple secondary alkyl bromides with aryl halides that contain sterically hindered C–X bonds: 1) ortho-substituted aryl bromides with nickel catalysts and 2) di-ortho-substituted aryl iodides with cobalt catalysts. Stoichiometric experiments and deuterium labeling studies show that 1) [Co] is better than [Ni] for oxidative addition of di-ortho-substituted Ar–I and 2) [Co] is better than [Ni] for radical capture/reductive elimination steps with di-ortho-substituted arenes. For both metals, Ar–H side products observed in reactions with low-yielding di-ortho-substituted aryl iodides appear to arise from Ar• formation and hydrogen-atom transfer from the solvent. While the origins of the differences in scope are not yet understood, these studies demonstrate a previously unknown complementarity between nickel and cobalt in cross-electrophile coupling.

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Direct (LC-)MS Identification of Regioisomers from C–H Functionalization by Partial Isotopic Labeling

C–H functionalization of complex substrates is highly enabling in total synthesis and in the development of late-stage drug candidates. Much work has been dedicated to developing new methods as well a...

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Electronic Spectroscopy of the Halogenated Criegee Intermediate, ClCHOO: Experiment and Theory

A chlorine-substituted Criegee intermediate, ClCHOO, is photolytically generated using a diiodo precursor, detected by VUV photoionization at 118 nm, and spectroscopically characterized via ultraviole...

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On the Integrity of Accurate Mass Measurement Data in Compound Characterization

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