Search NASA⌕ Search

Engineering topics

Schomaker, Jennifer M.

Publications and source records attributed to Schomaker, Jennifer M..

3 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Divergent C–H Amidations and Imidations by Tuning Electrochemical Reaction Potentials

Electrochemical C–H functionalizations are attractive transformations, as they are capable of avoiding the use of transition metals, pre-oxidized precursors, or suprastoichiometric amounts of terminal oxidants. Herein an electrochemically tunable method was developed that enabled the divergent formation of cyclic amines or imines by applying different reaction potentials. Detailed cyclic voltammetry analyses, coupled with chronopotentiometry experiments, were carried out to provide insight into the mechanism, while atom economy was assessed through a paired electrolysis. Finally, selective C–H amidations and imidations were achieved to afford five- to seven-membered sulfonamide motifs that could be employed for late-stage modifications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

An Enantiotropic Disorder–Partial Order Solid-State Transformation in a Molecular Solid Involving a Phase with Z ' = 12

A structural study of the complex aminated stereotriads, [( tert -butyldimethylsilyl)oxy]-4-ethynyl-4-(1-fluorohexyl)-1,2,3-oxathiazocane-2,2-dione (1) and its reduced analogue, [( tert -butyldimethylsilyl)oxy]-4-ethenyl-4-(1-fluorohexyl)-1,2,3-oxathiazocane-2,2-dione (2), revealed a k 12-type second-order phase transition in 1 and phase stability of 2 over the temperature range 100–400 K. The observed phase change in 1 has been linked to the partial ordering of the extensive positional disorder of the high temperature phase upon cooling as revealed by single-crystal X-ray diffraction. The ordering breaks the translational symmetry, introduces differences in the molecular volumes of the packed species, and results in a low-temperature crystal structure with Z '=12. The in situ powder X-ray diffraction studies suggest that the transition occurs between 237 K and 180 K upon cooling, but complete amorphization in the range of 244–274 K during heating complicated the assignment of the transition temperature. Lastly, the observed loss of crystallinity has been linked to the phase transition and implies that the loss of long range order is due to the crystallites undergoing the transformation independently from one another.

36 MATERIALS SCIENCE↗