A Mass Spectrometric Labeling Strategy for High-Throughput Reaction Evaluation and Optimization: Exploring C-H Activation This work was supported by the Director, Office of Energy Research, Office of Basic Energy Sciences, Chemical Sciences Division, U.S. Department of Energy, under contract No. DE-AC03-76SF00098. We are grateful to the National Institutes of Health for support (GM-50353) and for a Postdoctoral Fellowship to J.W.S.