Details of the electronic and geometric structures of stationary points along the reaction coordinate of the Newman Kwart rearrangement, which transforms an O-arylthiocarbamate to an S-arylcarbamothioate, are examined using quantum chemical methods for a large number of compounds considering both the thermal reactions of uncharged substrates as well as the corresponding reactions of radical cation substrates generated under photoredox conditions. The uncharged mechanism, which has intrinsically high 298 K free energies of activation (in excess of 30 kcal.mol-1), has the character of nucleophilic aromatic substitution and is thus accelerated by electron-withdrawing substituents on the aromatic ring. The radical cationic mechanism, by contrast, has 298 K free energies of activation that are typically below 20 kcal.mol-1, and is accelerated by electron donating substituents on the aromatic ring, which stabilize the hole character that is transferred to this fragment from the thiocarbamate fragment as the reaction proceeds. Opportunities to further accelerate the radical cation reaction are revealed by computational assessment of alternative amino groups for the thiocarbamate functionality. File list (5) download file view on ChemRxiv QCC_NK_181208.pdf (0.90 MiB) download file view on ChemRxiv QCC_NK_181208.docx (1.88 MiB) download file view on ChemRxiv QCC_NK_SI_181208.docx (192.73 KiB) download file view on ChemRxiv QCC_NK_SI_181208.pdf (412.48 KiB) download file view on ChemRxiv Geometries.xyz (479.10 KiB)

Temperature can affect many biological and chemical processes within a body. During in vivo measurements, varied temperature can impact the accurate quantification of additional abiotic factors such as oxygen. During magnetic resonance imaging (MRI) measurements, the temperature of the sample can increase with the absorption of radiofrequency energy, which needs to be well-regulated for thermal therapies and long exposure. To address this potentially confounding effect, temperature can be probed intentionally using reporter molecules to determine the temperature in vivo. This work describes a combined experimental and computational approach for the design of fluorinated molecular temperature sensors with the potential to improve the accuracy and sensitivity of 19 F MRI-based temperature monitoring. These fluorinated sensors are being developed to overcome the temperature sensitivity and tissue limitations of the proton resonance frequency (10 × 10 −3 ppm °C−1 ), a standard parameter used for temperature mapping in MRI. Here, we develop (perfluoro-[1,1′-biphenyl]-4,4′-diyl)bis((heptadecafluorodecyl)sulfane), which has a nearly 2-fold increase in temperature responsiveness, compared to the proton resonance frequency and the 19 F MRI temperature sensor perfluorotributylamine, when tested under identical NMR conditions. While 19 F MRI is in the early stages of translation into clinical practice, development of alternative sensors with improved diagnostic abilities will help advance the development and incorporation of fluorine magnetic resonance techniques for clinical use.

The solid state and fluxional behaviors in solution of complexes L2AlOBn and L7AlOBn (Bn = benzyl) supported by an analog of salen incorporating indolide arms connected via their 2- and 7-positions were defined by experiment and theory. The complexes catalyze the stereoselective conversion of rac-lactide (rac-LA) to isotactically enriched polylactide. A key aspect of the stereocontrol was examined through study of the initiation reactions via NMR spectroscopy, X-ray crystal structures of the ring-opened products, and theory. The results include the first unambiguous structural definition of stereocontrol in ring-opening of LA by a metal–alkoxide complex and the finding that definition of the stereochemistry of initiation by the studied system is governed thermodynamically rather than kinetically.

Details of the electronic and geometric structures of stationary points along the reaction coordinate of the Newman Kwart rearrangement, which transforms an O-arylthiocarbamate to an S-arylcarbamothioate, are examined using quantum chemical methods for a large number of compounds considering both the thermal reactions of uncharged substrates as well as the corresponding reactions of radical cation substrates generated under photoredox conditions. The uncharged mechanism, which has intrinsically high 298 K free energies of activation (in excess of 30 kcal.mol–1), has the character of nucleophilic aromatic substitution and is thus accelerated by electron-withdrawing substituents on the aromatic ring. The radical cationic mechanism, by contrast, has 298 K free energies of activation that are typically below 20 kcal.mol–1, and is accelerated by electron donating substituents on the aromatic ring, which stabilize the hole character that is transferred to this fragment from the thiocarbamate fragment as the reaction proceeds. Opportunities to further accelerate the radical cation reaction are revealed by computational assessment of alternative amino groups for the thiocarbamate functionality.

Details of the electronic and geometric structures of stationary points along the reaction coordinate of the Newman Kwart rearrangement, which transforms an O-arylthiocarbamate to an S-arylcarbamothioate, are examined using quantum chemical methods for a large number of compounds considering both the thermal reactions of uncharged substrates as well as the corresponding reactions of radical cation substrates generated under photoredox conditions. The uncharged mechanism, which has intrinsically high 298 K free energies of activation (in excess of 30 kcal.mol–1), has the character of nucleophilic aromatic substitution and is thus accelerated by electron-withdrawing substituents on the aromatic ring. The radical cationic mechanism, by contrast, has 298 K free energies of activation that are typically below 20 kcal.mol–1, and is accelerated by electron donating substituents on the aromatic ring, which stabilize the hole character that is transferred to this fragment from the thiocarbamate fragment as the reaction proceeds. Opportunities to further accelerate the radical cation reaction are revealed by computational assessment of alternative amino groups for the thiocarbamate functionality.