Exocyclic push–pull conjugated compounds. Part 2. The effect of donor and acceptor substituents on the rotational barrier of push–pull ethylenes

Silenes: Connectors between classical alkenes and nonclassical heavy alkenes

“…Their conclusions were based on MP4/6-311(d)//MP2/6-31G(d) calculations for RR Si CH 2 species and were determined in two ways: from the calculated enthalpies of dehydrogenation of the corresponding ethylhydrosilanes into the dimethylsilenes, and from extrapolations using frozen equilibrium geometries with R-Si C-H twist angles up to 60 • . This last method was successfully applied by Benassi to determine rotational barriers in alkenes [79]. Both methods showed that the higher the electronegativity of the substituent at Si, the shorter and weaker the Si C -bond.…”

Push–pull alkenes by reacting N,N′-dimethyl cyclic ketene N,N′-acetals with isocyanates: synthesis, structures, and reactivities

“…[9][10][11] These special properties provided impetus for the synthesis, characterization, and applications of push-pull alkenes 12-24 along with theoretical investigations to understand and predict these effects. [25][26][27][28][29][30][31] Recently, Pittman's group 32,33 reported the reactions of cyclic ketene-N,X-acetals (X = O, S) with isocyanates and isothiocyanates to generate push-pull alkenes in excellent yields. In this Letter, the conversion of cyclic ketene-N,N-acetals 2 and 3 to sterically crowded push-pull alkenes via reactions with isocyanates will be demonstrated and discussed for the first time.…”

Reexamination of the π‐bond strengths within H2C=XHn systems: A theoretical study

“…One of the best theoretical approaches may be to measure the torsional barrier about a double bond, for which some quantitative results have been reported 4–7. This approach assumed that the rotational transition state (TS) had no π‐bond character, but another π‐bond interaction, e.g., hyperconjugation or conjugation with lone pairs on the hetero atom, might be present in the rotational TS.…”