PyQuiverHS: A Web Tool for Computing Isotope Effects

ABSTRACT Predicting isotope effects using electronic structure calculations is widely done, but current software options can present a barrier for some chemists, depending upon their needs and software/programming proficiency. Building upon existing code bases, we have developed PyQuiverHS as a free web tool ( www.isotope‐effects.com ) to provide ready access to kinetic and equilibrium isotope effect (EIE) calculations employing the Bigeleisen–Mayer (B‐M) and enthalpy–entropy ( H‐S ) partition functions. A graphical user interface assists in setting up a configuration file, which contains scaling factor and isotope substitution information. After uploading the configuration file and Gaussian frequency jobs for the unlabeled system, users execute a kinetic isotope effect (KIE) or EIE calculation at a particular temperature or range of temperatures with a defined increment. Wigner and Bell tunneling corrections are provided for KIE calculations. Overall KIEs or EIEs and their contributing B‐M and H‐S terms are compiled in auto‐downloaded comma‐separated values (*.csv) and plain text files. Automating the process with PyQuiverHS is a significant gain in efficiency, as previous methods for these types of calculations have relied on spreadsheets, which require time‐intensive data manipulation. We demonstrate the utility of PyQuiverHS by calculating temperature‐dependent conformational KIEs in 9,10‐dihydro‐4,5‐dimethylphenanthrene ( 1 ), a doubly bridged biphenyl derivative ( 2 ), [2.2]‐metaparacyclophane ( 3 ), a secondary KIE for the S N 2 reaction of chloride with methyl bromide ( 4 ), and an EIE for the interconversion of chair conformations of 1,1,3,3‐tetramethylcyclohexane ( 6 ).