The single-crystal X-ray diffraction structure of the sodium salt of N- (3-(aminosulfonyl)-4-chloro-2-hydroxyphenyl)-N′- (2,3-dichlorophenyl) urea at 173 K is reported. The structure contains 3 mol of water situated in distinct channels in the vicinity of the sodium cation. Powders of this phase undergo isomorphic dehydration, losing 0.5% w/w water between 90 and 15% relative humidity (RH) at 25 °C without changing the powder X-ray pattern. Below 15% RH and above 50 °C, additional dehydration occurs in conjunction with a reversible phase transition. A third semicrystalline dehydrated phase appears after vacuum-drying and at high temperatures and also can be reversibly rehydrated to the original form. Single crystals of the dehydrated phases could not be prepared, so a combination of methods were used to understand the structural changes occurring during the desolvation process, including thermal analysis, vapor sorption measurements, variable-humidity and variable-temperature powder X-ray diffraction, vibrational spectroscopy, and 1 H, 13 C, 15 N, and 23 Na magic-angle spinning (MAS) solid-state NMR. The uptake of water vapor into the trihydrate form was investigated by NMR and vibrational spectroscopy using isotopically labeled water. Static 2 H and 17 O NMR quadrupolar line shape analysis combined with changes in MAS spectra showed exchanged sites on the parent and water molecules. The results indicate that two moles of ion-associated water in the larger tunnel are more labile than a hydrogen-bonded mole of water. Entire water molecules can exchange into the lattice to a small extent, but more efficient hydrogen transfer exchange is observed in the main channel and a smaller perpendicular side channel. The exchanged water deuterons execute rapid three-site jump motions at 273 K.

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Malonic anhydrides decompose at or below room temperature, to form a ketene and carbon dioxide. Rate constants for the thermal decomposition of malonic, methylmalonic, and dimethylmalonic anhydrides were measured by NMR spectroscopy at various temperatures, and activation parameters were evaluated from the temperature dependence of the rate constants. Methylmalonic anhydride is the fastest, with the lowest ΔH(‡), and dimethylmalonic anhydride is the slowest. The nonlinear dependence on the number of methyl groups is discussed in terms of a concerted [2(s) + (2(s) + 2(s))] or [2(s) + 2(a)] cycloreversion that proceeds via a twisted transition-state structure, supported by computations.

Wirkung und Ursache: Sekundäre Deuteriumisotopeneffekte auf die Acidität der deuterierten Verbindungen 1–4 wurden mithilfe einer NMR‐Titrationsmethode gemessen, die auf Mischungen anwendbar und durch sehr hohe Genauigkeit gekennzeichnet ist. Temperaturabhängige Messungen ergaben als alleinige Ursache der Isotopeneffekte Änderungen der Schwingungsfrequenzen, was eine induktive Ursache ausschließt.