Highly stereoselective decarboxylation of (+)-1-Bromo-1-chloro-2,2,2-trifluoropropanoic acid gives (+)-1-Bromo-1-chloro-2,2,2-trifluoroethane ((+)-Halothane) with retention of configuration

The absolute configuration of the title acid (2) has been determined to be S by X-ray crystallography. Thus, decarboxylation of 2 produces (S)-(+)-halothane with 99% retention of configuration. This behavior is compared to other stereoselective decarboxylation reactions of ?-haloacids from the literature that also give high degrees of retention of configuration when in the form of their quaternary ammonium salts, which contain one proton. The proton of the ammonium salt is necessary to protonate the anionic intermediate formed from decarboxylation. In the absence of this relatively acidic proton, we had previously found that using triethylene glycol (TEG) as both solvent and proton source for the decarboxylation reaction of acid 2 caused poor stereoselectivity. This was in contrast to 1,2,2,2-tetrafluoro-1-methoxypropionic acid (6), which showed a high degree of retention of configuration in TEG. To rationalize this differing behavior we report DFT studies at PCM-B3LYP/6-31++G** level of theory (the results were additionally confirmed with 6-311++G** and aug-cc-pVDZ basis sets). The energy barrier to inversion of configuration of the anionic reaction intermediate of acid 2 (11) is 10.23 kcal/mol. However, we find that the anionic intermediate from acid 6 (10) would rather undergo ?-elimination instead of inversion of configuration. Thus the planar transition state required for inversion of configuration is never reached, regardless of the rate of proton transfer to the anion

Thermochromicity in Wool Dyed with 6-Bromoindigo Depends on the Presence and Identity of a Solvent

The thermochromic effect of wool dyed with 6-bromoindigo was found to depend on both heat and a solvent. The dyed fabric must be immersed in a solvent while heating for a color change from purple to blue to occur. Ethanol was the most effective solvent in causing the color change. Water was effective as well. 1-Butanol caused a slight color change, while toluene was completely ineffective. These results are interpreted as interaction of the solvent with both the wool surface and adsorbed dye molecular aggregates, causing changes in the size of large red aggregates to smaller blue ones. The mildest conditions for the color change, immersion in water at 60 °C, are so easily obtained that it is possible that ancient dyers knew of this as a finishing process for their dyeing, or knew to avoid post-dyeing heat treatment

Legislative Documents

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NMR Spectroscopic and Computational Study of Conformational Isomerism in Substituted 2‑Aryl‑3<i>H</i>‑1-benzazepines: Toward Isolable Atropisomeric Benzazepine Enantiomers

Certain 2-aryl-3<i>H</i>-1-benzazepines are conformationally mobile on the NMR time scale. Variable-temperature NMR experiments bolstered by calculations indicate that alkylation of the azepine ring will slow the interconversion of conformational enantiomers markedly. DFT studies show that, while the substitution patterns of the aryl groups at C2 and C4 do not exert large effects on the rate of enantiomerization, alkylation at C5 slows it appreciably. Alkylation at C3 slows enantiomerization even more, possibly to the extent that isolation of atropisomers might be attempted

Interplay of Nitrogen-Atom Inversion and Conformational Inversion in Enantiomerization of 1<i>H</i>‑1-Benzazepines

A series of 2,4-disubstituted 1<i>H</i>-1-benzazepines, <b>2a</b>–<b>d</b>, <b>4</b>, and <b>6</b>, were studied, varying both the substituents at C2 and C4 and at the nitrogen atom. The conformational inversion (ring-flip) and nitrogen-atom inversion (N-inversion) energetics were studied by variable-temperature NMR spectroscopy and computations. The steric bulk of the nitrogen-atom substituent was found to affect both the conformation of the azepine ring and the geometry around the nitrogen atom. Also affected were the Gibbs free energy barriers for the ring-flip and the N-inversion. When the nitrogen-atom substituent was alkyl, as in <b>2a</b>–<b>c</b>, the geometry of the nitrogen atom was nearly planar and the azepine ring was highly puckered; the result was a relatively high-energy barrier to ring-flip and a low barrier to N-inversion. Conversely, when the nitrogen-atom substituent was a hydrogen atom, as in <b>2d</b>, <b>4</b>, and <b>6</b>, the nitrogen atom was significantly pyramidalized and the azepine ring was less puckered; the result here was a relatively high energy barrier to N-inversion and a low barrier to ring-flip. In these N-unsubstituted compounds, it was found computationally that the lowest-energy stereodynamic process was ring-flip coupled with N-inversion, as N-inversion alone had a much higher energy barrier

Interplay of Nitrogen-Atom Inversion and Conformational Inversion in Enantiomerization of 1<i>H</i>‑1-Benzazepines

A series of 2,4-disubstituted 1<i>H</i>-1-benzazepines, <b>2a</b>–<b>d</b>, <b>4</b>, and <b>6</b>, were studied, varying both the substituents at C2 and C4 and at the nitrogen atom. The conformational inversion (ring-flip) and nitrogen-atom inversion (N-inversion) energetics were studied by variable-temperature NMR spectroscopy and computations. The steric bulk of the nitrogen-atom substituent was found to affect both the conformation of the azepine ring and the geometry around the nitrogen atom. Also affected were the Gibbs free energy barriers for the ring-flip and the N-inversion. When the nitrogen-atom substituent was alkyl, as in <b>2a</b>–<b>c</b>, the geometry of the nitrogen atom was nearly planar and the azepine ring was highly puckered; the result was a relatively high-energy barrier to ring-flip and a low barrier to N-inversion. Conversely, when the nitrogen-atom substituent was a hydrogen atom, as in <b>2d</b>, <b>4</b>, and <b>6</b>, the nitrogen atom was significantly pyramidalized and the azepine ring was less puckered; the result here was a relatively high energy barrier to N-inversion and a low barrier to ring-flip. In these N-unsubstituted compounds, it was found computationally that the lowest-energy stereodynamic process was ring-flip coupled with N-inversion, as N-inversion alone had a much higher energy barrier