Quantum Mechanics Assisted Machine Learning LEF Library: LEF4000 and Tranche 2 Not all molecules could be processed by QM mainly due to missing stereochemistry information. Around 10% of the whole LEF5500 data set had ambiguous stereochemistry annotation. Only unassigned enantiomeric compounds could be rescued because their isomers are indistinguishable in NMR with achiral solvent and the stereocenter could therefore be assigned arbitrarily. Those molecules that could be processed were used in the QM assisted ML workflow and the subsequent comparison.