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

• is illustrated by another classical textbook example, the coalescence of the NMR signals of N,N-dimethylformamide, which can be brought about by gentle warming. Separable amide rotamers are usually regarded as laboratory curiosities and are not expected in the absence of sterical congestion. During

• synthetic work in the morphinan series, we encountered a remarkable behavior of an unhindered formamide which produced double bands in TLC. We initially attributed this behavior to the undesired formation of diastereomers as even at 150 °C, no coalescence of the 1H NMR signals of the formyl protons could be

• deduced a value of 94 kJ/mol from a coalescence temperature of 170 °C but did not provide crucial data such as the spectrometer frequency required for the calculation. Sulima et al. reported a rotational barrier of 92 kJ/mol for 1-bromo-N-formyl-4-hydroxy-3-methoxymorphinan-6-one based on dynamic NMR

Structure of 1,5-benzodiazepinones in the solid state and in solution: Effect of the fluorination in the six-membered ring

• Marta Pérez-Torralba,
• Rosa M. Claramunt,
• M. Ángeles García,
• Concepción López,
• M. Carmen Torralba,
• M. Rosario Torres,
• Ibon Alkorta and
• José Elguero

Beilstein J. Org. Chem. 2013, 9, 2156–2167, doi:10.3762/bjoc.9.253

• experimental inversion barriers of 3a, 5a (twice) and 6a have been determined and are given in Table 4. We have calculated those of 1a and 2a. The barriers for an AB system that become an A2 one depend on three values: i) the coalescence temperature TC; ii) the difference in Hz of the protons of the AB system

• (ΔνAB), and iii) the geminal coupling constant, JAB (or Jae). The inversion rate at the coalescence temperature for an AB system is given by kC = π/√2·√Δν2 + 6 JAB2 [11] and the barrier by the modified Eyring equation [24][25][26], ΔG‡ = 19.12·TC (10.32 + log TC/kC) [18][19][20]. From the values in

Dipolar addition to cyclic vinyl sulfones leading to dual conformation tricycles

• Steven S. Y. Wong,
• Michael G. Brant,
• Christopher Barr,
• Allen G. Oliver and
• Jeremy E. Wulff

Beilstein J. Org. Chem. 2013, 9, 1419–1425, doi:10.3762/bjoc.9.159

• 1H NMR signals below 330 K, with a coalescence temperature of approximately 280 K. At lower temperatures, two distinct conformations could be identified; by 213 K these were sufficiently well-resolved to permit integration (revealing a ≈7:1 ratio of the two conformers) and more extensive NMR analysis

Self-assembled organic–inorganic magnetic hybrid adsorbent ferrite based on cyclodextrin nanoparticles

• Ângelo M. L. Denadai,
• Frederico B. De Sousa,
• Joel J. Passos,
• Fernando C. Guatimosim,
• Kirla D. Barbosa,
• Ana E. Burgos,
• Fernando Castro de Oliveira,
• Jeann C. da Silva,
• Bernardo R. A. Neves,
• Nelcy D. S. Mohallem and
• Rubén D. Sinisterra

Beilstein J. Org. Chem. 2012, 8, 1867–1876, doi:10.3762/bjoc.8.215

• , suggesting that βCD is able to minimize the ferrite coalescence process in aqueous solution. The ferrite aggregation process may occur in low zeta potential values (−10 mV, see zeta potential data) and is insufficient to avoid van der Waals attraction [30]; however, at pH 7 this self-assembly behavior can

Restructuring polymers via nanoconfinement and subsequent release

• Alan E. Tonelli

Beilstein J. Org. Chem. 2012, 8, 1318–1332, doi:10.3762/bjoc.8.151

• extension of the included guest polymer chains, which leads, following the careful removal of the host molecule lattice, to unique behaviors for the bulk coalesced polymer samples. Apparently, substantial degrees of the extended and unentangled natures of the IC-included chains are retained upon coalescence

• . In this review we summarize the behaviors and uses of coalesced polymers, and attempt to draw conclusions on the relationship between their behavior and the organization/structures/conformations of the constituent polymer chains achieved upon coalescence from their ICs. Keywords: cyclodextrins

• ) and their characterization are similar to those of polymer–CD ICs [69]. Coalescence and characterization of polymers from their CD ICs Guest polymers may be coalesced from their CD ICs in several ways [65]. Depending on their mode of formation, they may be washed with warm water, briefly treated with

Synthesis and antiviral activities of spacer-linked 1-thioglucuronide analogues of glycyrrhizin

• Christian Stanetty,
• Andrea Wolkerstorfer,
• Hassan Amer,
• Andreas Hofinger,
• Ulrich Jordis,
• Dirk Claßen-Houben and
• Paul Kosma

Beilstein J. Org. Chem. 2012, 8, 705–711, doi:10.3762/bjoc.8.79

• . Reversible coalescence of these signal groups was observed upon heating a solution of the N-acetyl derivative 11 up to 100 °C in DMSO-d6 and subsequent cooling to room temperature (Figure 2), supporting the assignment of two signal data sets for two rotamers. The orientation of the amide carbonyl group in

Synthesis of 5-(2-methoxy-1-naphthyl)- and 5-[2-(methoxymethyl)-1-naphthyl]-11H-benzo[b]fluorene as 2,2'-disubstituted 1,1'-binaphthyls via benzannulated enyne–allenes

• Yu-Hsuan Wang,
• Joshua F. Bailey,
• Jeffrey L. Petersen and
• Kung K. Wang

Beilstein J. Org. Chem. 2011, 7, 496–502, doi:10.3762/bjoc.7.58

• –carbon single bond connecting the 2-methoxyphenyl substituent to the C5 of the benzofluorenyl moiety. The rotational barrier was calculated to be at least 16.7 kcal/mol at 70 °C on the basis of the lack of coalescence of signals at this temperature. This lowest possible rotational barrier is

Miniemulsion polymerization as a versatile tool for the synthesis of functionalized polymers

• Daniel Crespy and
• Katharina Landfester

Beilstein J. Org. Chem. 2010, 6, 1132–1148, doi:10.3762/bjoc.6.130

• ; polymer colloids; polymerization; Review Introduction Miniemulsions are a special class of emulsions that are stabilized against coalescence (by a surfactant) and Ostwald ripening (by an osmotic pressure agent). The miniemulsions are produced by high-energy homogenization and usually yield stable and

Ring strain and total syntheses of modified macrocycles of the isoplagiochin type

• Andreas Speicher,
• Timo Backes,
• Kerstin Hesidens and
• Jürgen Kolz

Beilstein J. Org. Chem. 2009, 5, No. 71, doi:10.3762/bjoc.5.71

• NMR investigations from −20 up to 55 °C resulted in coalescence of the methoxy signals. By an approximation method [16] as well as by exact line form analysis [17] the rotation barrier could be calculated to ~66 kJ/mol indicating that the conformers are stable within the NMR time scale but cannot be

A biphasic oxidation of alcohols to aldehydes and ketones using a simplified packed- bed microreactor

• Andrew Bogdan and
• D. Tyler McQuade

Beilstein J. Org. Chem. 2009, 5, No. 17, doi:10.3762/bjoc.5.17

• allowed the immiscible bleach (adjusted to pH 9.1 using NaHCO3) and organic alcohol solutions to form plugs before reaching the packed bed (Figure 2A). When passing through the AO-TEMPO catalyst bed, the plugs emulsified, as indicated by visual inspection and by the plug coalescence at the microchannel

• coalescence of drops at the outlet of the microchannel (B). The long-term activity of AO-TEMPO packed beds in the oxidation of 4-chlorobenzyl alcohol. A solution of 4-chlorobenzyl alcohol (0.2 M in CH2Cl2) set to 44 μL min−1 (8.8 μmol min−1, 1.0 equiv min−1) and an aqueous solution consisting of NaOCl (0.25 M

Stereoselective synthesis of (2S,3S,4Z)-4-fluoro- 1,3-dihydroxy- 2-(octadecanoylamino)octadec- 4-ene, [(Z)-4-fluoroceramide], and its phase behavior at the air/water interface

• Gergana S. Nikolova and
• Günter Haufe

Beilstein J. Org. Chem. 2008, 4, No. 12, doi:10.3762/bjoc.4.12

• networks, because its polar head groups can act both as acceptor and as a donor, ceramide, when added or generated in situ in the membrane, can segregate from the other lipids and cause coalescence of the small lipid raft domains to give highly ordered ceramide-enriched domains. Moreover, due to the small