Strong hyperconjugative interactions limit solvent and substituent influence on conformational equilibrium: the case of cis-2-halocyclohexylamines

• Camila B. Francisco,
• Cleverton S. Fernandes,
• Ulisses Z. de Melo,
• Roberto Rittner,
• Gisele F. Gauze and
• Ernani A. Basso

Beilstein J. Org. Chem. 2019, 15, 818–829, doi:10.3762/bjoc.15.79

• group and equatorial halogen) and ea (equatorial amine group and axial halogen) conformers (Figure 1) by dynamic NMR (DNMR) and theoretical calculations. Results and Discussion Experimental conformational population Low-temperature NMR experiments allow the identification of the individual conformers

• all compounds. Conclusion The conformational behavior of the cis isomers of 2-fluoro-, 2-chloro- and 2-bromocyclohexylamine was determined experimentally through DNMR at −80 °C, with populations of the ea conformer (equatorial amine group and axial halogen) higher than 90% in dichloromethane-d2 and

One hundred years of benzotropone chemistry

• Arif Dastan,
• Haydar Kilic and
• Nurullah Saracoglu

Beilstein J. Org. Chem. 2018, 14, 1120–1180, doi:10.3762/bjoc.14.98

• ) and monosubstituted tetrahydro-7H-benzo[7]annulenone, St-Jacques' group benefited extensively from the use of dynamic nuclear magnetic resonance (DNMR) techniques [126][127]. A catalytic deuterogenation of 4,5-benzotropone (11) followed by deuteration led to deuterated 5,6,8,9-tetrahydro-7H-benzo[7

One-pot three-component route for the synthesis of S-trifluoromethyl dithiocarbamates using Togni’s reagent

• Azim Ziyaei Halimehjani,
• Martin Dračínský and
• Petr Beier

Beilstein J. Org. Chem. 2017, 13, 2502–2508, doi:10.3762/bjoc.13.247

• DFT calculations. Figure 1 depicts variable temperature 1H NMR spectra of compound 4c. The coalescence of the methyl signals can be observed at 308 K, whereas the coalescence of the CH2 signals would require an even higher temperature than 328 K. Complete lineshape analysis approach (dynamic NMR, dNMR

• determined using this approach (15.9 kcal/mol) is almost identical to that obtained by the dNMR approach and is higher compared to the corresponding nonfluorinated analogue [35][38][39]. The rotational barriers obtained for compounds 4a–c are summarized in Table 2. The structures of compounds 4a–c was

An experimental and theoretical NMR study of NH-benzimidazoles in solution and in the solid state: proton transfer and tautomerism

• Carla I. Nieto,
• Pilar Cabildo,
• M. Ángeles García,
• Rosa M. Claramunt,
• Ibon Alkorta and
• José Elguero

Beilstein J. Org. Chem. 2014, 10, 1620–1629, doi:10.3762/bjoc.10.168

• C5/C6) of NH-benzimidazoles that, in some solvents and in the solid state, appear different (blocked tautomerism). In the case of 1H-benzimidazole itself we have measured the prototropic rate in HMPA-d18. Keywords: CPMAS; DNMR; GIAO; proton transfer; tautomerism; Introduction Of almost any class of

• four NH-benzimidazoles: 1 and 3 yielded average signals in DMSO-d6 and only in HMPA-d18 the prototropic exchange was slow, on the other hand 2 and 4 behaved as if the tautomerism was blocked in DMSO-d6. In the case of 1 a dynamic NMR (DNMR) study in HMPA-d18 was performed (Figure 6). The relevant data

• substituents at positions 4(7) or 5(6), for instance, in the case of omeprazole, a 5(6)-methoxy-1H-benzimidazole derivative [35][36]. Besides, solid state results as well as GIAO calculations provide new data to characterize this important family of compounds. Finally, by means of DNMR experiments it was

Chromatographically separable rotamers of an unhindered amide

• Mario Geffe,
• Lars Andernach,
• Oliver Trapp and
• Till Opatz

Beilstein J. Org. Chem. 2014, 10, 701–706, doi:10.3762/bjoc.10.63

• quantitatively by refluxing 3 in ethyl formate (Scheme 1). Dynamic NMR (DNMR) measurements (400 MHz) on a sample of 4 in DMSO-d6 at temperatures ranging from 20 °C to 150 °C, the upper limit for technical reasons, showed no signs of beginning coalescence of the formyl proton resonances even at the highest

• ‡ (293 K) = 93.2 ± 0.1 kJ/mol (E to Z) respectively (Figure 1, Figure 2). Dynamic HPLC studies Like the DNMR data, the simple kinetic analysis only permits the determination of the free activation energy while the separation of entropic and enthalpic contributions requires a variation of the temperature

The chemistry of bisallenes

• Henning Hopf and
• Georgios Markopoulos

Beilstein J. Org. Chem. 2012, 8, 1936–1998, doi:10.3762/bjoc.8.225