The autoencoder, from which the Spec2Mol decoder had derived, was pre-trained on about 110 million molecules which were sourced from the PubChem dataset . The structures of the molecules in the PubChem dataset are represented using the SMILES notation . Stereochemistry information was not indicated in the SMILES representation. The reason for not accounting for stereochemistry is that in the subsequent task of spectra translation recovering stereochemistry information from the mass spectra is especially challenging or possibly even impossible and therefore it is out of the scope of this work.