Aid on Demand: African Leaders and the Geography of China's Foreign Assistance

This article investigates whether China’s foreign aid is particularly prone to political capture by political leaders of aid-receiving countries. Specifically, we examine whether more Chinese aid is allocated to the political leaders’ birth regions and regions populated by the ethnic group to which the leader belongs, controlling for indicators of need and various fixed effects. We have collected data on 117 African leaders’ birthplaces and ethnic groups and geocoded 1,650 Chinese development finance projects across 3,097 physical locations committed to Africa over the 2000-2012 period. Our econometric results show that current political leaders’ birth regions receive substantially larger financial ows from China than other regions. On the contrary, when we replicate the analysis for the World Bank, our regressions with region-fixed effects show no evidence of such favoritism. For Chinese and World Bank aid alike, we also find no evidence that African leaders direct more aid to areas populated by groups who share their ethnicity, when controlling for region-fixed effects

Examining the Ways To Bend and Break Reaction Pathways Using Mechanochemistry

Mechanical forces can lead to qualitative changes in reaction mechanism, which depend on the specific mode of force induction and inherent chemistries of the mechanophore. To demonstrate these effects at an atomistic level, three challenging mechanochemical transformations of recent interest are herein studied: spiropyran ring opening, flex-activated small molecule release, and cyclopropane ring opening. These examples show that mechanical load can eliminate intermediates and transition states along a reaction path, preactivate reactions where the force is not parallel to the reaction path, and modulate force conveyance to the mechanophore in a polymer-dependent fashion. Two different merocyanin products were identifiedcis and trans isomersfrom the spiropyran ring-opening reaction, and tuning the magnitude of the force allows for selection of one over the other. The reaction involving oxanorbornadiene where bonds perpendicular to the force are flexed through angular distortions has the interesting property that while the central bond contracts, the overall molecule is lengthened to effect activation. Cyclopropane ring openings demonstrate that the larger the extension of the mechanophore, determined by the rigidity of the polymer backbone under applied force, the larger the change in activation barrier. In this case, the application of a force represents a preactivation mechanism where the initial structure rises in energy, while the transition state stays relatively constant. For these three motifs, the reaction paths are readily uncovered using the growing string method, showing it to be a widely useful tool for studying mechanochemistry

An Ion‐Pairing Approach to Stereoselective Metal‐Free Ring‐Opening Metathesis Polymerization

Stereochemistry can have a profound impact on polymer and materials properties. Unfortunately, straightforward methods for realizing high levels of stereocontrolled polymerizations are often challenging to achieve. In a departure from traditional metal‐mediated ring‐opening metathesis polymerization (ROMP), we discovered a remarkably simple method for controlling alkene stereochemistry in photoredox mediated metal‐free ROMP. Ion‐pairing, initiator sterics, and solvation effects each had profound impact on the stereochemistry of polynorbornene (PNB). Simple modifications to the reaction conditions produced PNB with trans alkene content of 25 to >98 %. High cis content was obtained from relatively larger counterions, toluene as solvent, low temperatures (−78 °C), and initiators with low Charton values. Conversely, smaller counterions, dichloromethane as solvent, and enol ethers with higher Charton values enabled production of PNB with high trans content. Data from a combined experimental and computational investigation are consistent with the stereocontrolling step of the radical cationic mechanism proceeding under thermodynamic control.Stereoselective ring‐opening metathesis polymerization is achieved by non‐covalent interactions, such as ion‐pairing, initiator sterics and solvation effects, in a metal‐free condition.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/168268/1/ange202016393.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/168268/2/ange202016393_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/168268/3/ange202016393-sup-0001-misc_information.pd

Mechanochemical Release of N

We have discovered a new flex‐activated mechanophore that releases an N‐heterocyclic carbene (NHC) under mechanical load. The mechanophore design is based upon NHC‐carbodiimide (NHC‐CDI) adducts and demonstrates an important first step toward flex‐activated designs capable of further downstream reactivities. Since the flex‐activation is non‐destructive to the main polymer chains, the material can be subjected to multiple compression cycles to achieve iterative increases in the activation percentage of mechanophores. Two different NHC structures were demonstrated, signifying the potential modularity of the mechanophore design.A new kind of flex‐activated mechanophore, N‐heterocyclic carbene–carbodiimide adduct (NHC‐CDI), was developed as a platform to release different NHCs under mechanical load. The polymeric materials containing NHC‐CDI can be subjected to multiple compression cycles and successively release NHCs, which have potential to be utilized as self‐healing, self‐strengthening and self‐reporting materials.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/167837/1/ange202100576-sup-0001-misc_information.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/167837/2/ange202100576.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/167837/3/ange202100576_am.pd