N-Trifyl substituted 1,4-diheterocyclohexanes—stereodynamics and the Perlin effect

Conformational analysis of 4,4‐dimethyl‐1‐(trifluoromethylsulfonyl)‐1,4‐azasilinane and 2,2,6,6‐tetramethyl‐4‐(trifluoromethylsulfonyl)‐1,4,2,6‐oxazadisilinane

“…The value of Δ G c ≠ for compound 1 (Table ) is equal to that found by us earlier for 4‐(trifluoromethylsulfonyl)morpholine (12.9 kcal mol −1 ) . At the same time, Δ G c ≠ for compound 2 (Table ) is much higher than those for its N‐alkyl analogs 4 and 5 (8.5 and 7.7 kcal mol −1 ) .…”

“…The other signals and the 19 F lines in both compounds are sharp at room or higher temperature. For this reason the 19 F, 1 H, and 13 C NMR spectra of the two compounds were studied lowering the probe temperature; the corresponding freon mixture was employed as usual . Although in the 19 F NMR spectra no change was observed, both proton and carbon signals in the 1 H and 13 C NMR spectra show the expected decoalescence effects (cf.…”

“…The assignment of the major observed species of 1 to the outward conformer is confirmed not only by its lower calculated energy but also by practical coincidence of the 19 F NMR chemical shift of 1 (−76.33 ppm) with that of its analogs with X = CH 2 , O, SO 2 , CF 3 SO 2 N (~−76 ppm) (Scheme ) for which the outward location of the CF 3 group was evident from the low temperature 19 F NMR experiments; the corresponding inward conformers resonate at ca. −79 ppm …”

“…In this paper, we present the results of conformational studies of 4,4‐dimethyl‐1‐(trifluoromethylsulfonyl)‐1,4‐azasilinane 1 and 2,2,6,6‐tetramethyl‐4‐(trifluoromethylsulfonyl)‐1,4,2,6‐oxazadisilinane 2 as depicted in Schemes and , respectively, in comparison with our recent investigations of the reference compounds – 1‐(trifluoromethylsulfonyl)piperidine 3 as a non‐silylated analog of compound 1 , and 4‐alkyl‐2,2,6,6‐tetramethyl‐1,4,2,6‐oxazadisilinanes (alkyl = Me, 4 , or i ‐Pr, 5 ) as N‐alkyl analogs of compound 2 …”

Computational 19F NMR. 1. General features

“…Some early computational work (aimed at benchmarking and validation) included F 2 as test molecule, which proved to be challenging [26][27][28]. Interest in modeling 19 F shifts has steadily continued, and several papers have appeared in the last decade aimed at general structural issues, solution chemistry and physical organic chemistry, [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46] solid-state issues (especially the prediction of chemical shift tensors), [47][48][49][50][51][52][53][54][55][56][57][58][59][60][61][62][63][64] J-couplings [65][66][67][68][69][70][71][72]…”