Chemical reactions under high pressure. XVIII. Evidence for an anion-carbene pair

Abstract

The activation volume of the base-promoted solvolysis of l-chloro-3-methylbuta-l,2-diene in an ethanol-water mixture 80:20 vol/vol at 250 equals +5 cm3/mol. A combination of this value with that measured earlier for 3-chloro-3-methylbut-l-yne and with the densities of these two substrates shows that the two transition states have virtually identical volumes. This suggests that the two precursor anions are on their way to a common

Skipped diynes. V. Secondary diethynyl carbinols. Base-catalyzed ynol to enol rearrangements and ultraviolet spectra and conjugation

“…To summarize this section, we note that the base-catalyzed ynol -» enone rearrangement (eq [11][12][13][14] does not occur with alkyl ynols but appears to require at least a phenyl or extra ethynyl group to facilitate the formation of the anionic intermediates, e.g., 19. A number of strange-looking processes, eq [18][19][20][21], turn out to be straightforward once the basic rearrangement (eq 11, 13) is accepted.…”

Face Selection in Addition and Elimination in Sterically Unbiased Systems

“…We referred in section IIA to the neutral solvolysis of the propargyl chlorides E - and Z - 9 . When these same compounds are exposed to a basic medium, the resulting anions jettison chloride ion to give carbene-anion pairs, which in part undergo retentive isomerization to the allenes 10 and in part dissociate to the common free carbene 26 . This carbene has a strongly dipolar character, , and the dipole moment should increase because of induction as a nucleophile approaches.…”

From Solvolysis to Self-Assembly

“…Besides simple carbenes 8 , vinylidene carbenes 9a and allenidene carbenes 9b were already known. Vinylidene carbenes 9a were generated via the elimination of HX from primary vinyl halides by bases, deamination of vinyl amines, photofragmentation, and base decomposition of 5,5-disubstituted N -nitrosooxazolidones, none of which were ideal, whereas allenidene carbenes 9b were mostly generated from popargyl halides and/or haloallenes in the presence of bases …”