A laterally-fused N-heterocyclic carbene framework from polysubstituted aminoimidazo[5,1-b]oxazol-6-ium salts

• Andrew D. Gillie,
• Matthew G. Wakeling,
• Bethan L. Greene,
• Louise Male and
• Paul W. Davies

Beilstein J. Org. Chem. 2024, 20, 621–627, doi:10.3762/bjoc.20.54

• the C(oxazole)–N(sulfonamide) bond. No coalescence is observed at up to 110 °C indicating that these motifs might be useful as a robust atropisomeric system. The molecular structure of 13 and 14 have been unambiguously determined by single crystal X-ray diffraction (Scheme 2) [28]. The N–metal

Electron-beam-promoted fullerene dimerization in nanotubes: insights from DFT computations

• Laura Abella,
• Gerard Novell-Leruth,
• Josep M. Ricart,
• Josep M. Poblet and
• Antonio Rodríguez-Fortea

Beilstein J. Org. Chem. 2024, 20, 92–100, doi:10.3762/bjoc.20.10

• metadynamics simulations provide hints on structures for the initial steps of the irreversible phase 2 where bond formation and breaking lead to important structural reorganizations within the coalescence process. Keywords: DFT; dimerization; fullerene; molecular dynamics; peapods; Introduction Transmission

• -TEM images and movies will provide us a deeper understanding of fullerene coalescence processes in peapods. Computational Methods The Amsterdam Density Functional (ADF) code [21][22] was used for the electronic structure calculations and to optimize reactants, products, intermediates and transition

Benzoimidazolium-derived dimeric and hydride n-dopants for organic electron-transport materials: impact of substitution on structures, electrochemistry, and reactivity

• Swagat K. Mohapatra,
• Khaled Al Kurdi,
• Samik Jhulki,
• Georgii Bogdanov,
• John Bacsa,
• Maxwell Conte,
• Tatiana V. Timofeeva,
• Seth R. Marder and
• Stephen Barlow

Beilstein J. Org. Chem. 2023, 19, 1651–1663, doi:10.3762/bjoc.19.121

• broadening and then coalescence of some of these peaks on increasing the temperature, consistent with the room-temperature spectrum being affected by restricted rotation; interestingly the crystal structure of 1b2 contains molecules with two very different conformations (see below). The 12 dimers are

Radical chemistry in polymer science: an overview and recent advances

• Zixiao Wang,
• Feichen Cui,
• Yang Sui and
• Jiajun Yan

Beilstein J. Org. Chem. 2023, 19, 1580–1603, doi:10.3762/bjoc.19.116

• dissolved initiators in the liquid phase during the process. A suspending agent, e.g., polyvinyl alcohol (PVA), is added to the system to prevent coalescence. The viscosity in suspension polymerization is low throughout the process which brings good heat transfer and temperature control, and therefore well

Water-soluble host–guest complexes between fullerenes and a sugar-functionalized tribenzotriquinacene assembling to microspheres

• Si-Yuan Liu,
• Xin-Rui Wang,
• Man-Ping Li,
• Wen-Rong Xu and
• Dietmar Kuck

Beilstein J. Org. Chem. 2020, 16, 2551–2561, doi:10.3762/bjoc.16.207

• ten-fold sugar-functionalized pillar[5]arene [43]. Temperature-dependent 1H NMR spectroscopy of TBTQ-(OAcG)6 in DMSO-d6 was carried out in the range of 20–70 °C and revealed a slight decrease of the splitting of the aromatic proton resonances with increasing temperature, but no coalescence. While most

NMR Spectroscopy of supramolecular chemistry on protein surfaces

• Peter Bayer,
• Anja Matena and
• Christine Beuck

Beilstein J. Org. Chem. 2020, 16, 2505–2522, doi:10.3762/bjoc.16.203

• , line broadening and eventually coalescence of the signals from both species occurs. Often, the broadening of the signal results in a disappearing of the signal when the peak height drops below the noise level of the spectrum. In the case of intermediate-to-fast exchange, where most interactions with

Rearrangement of o-(pivaloylaminomethyl)benzaldehydes: an experimental and computational study

• Csilla Hargitai,
• Györgyi Koványi-Lax,
• Tamás Nagy,
• Péter Ábrányi-Balogh,
• András Dancsó,
• Gábor Tóth,
• Judit Halász,
• Angéla Pandur,
• Gyula Simig and
• Balázs Volk

Beilstein J. Org. Chem. 2020, 16, 1636–1648, doi:10.3762/bjoc.16.136

• ), and δC= (142.5) showed a considerable line-broadening (coalescence), revealing a partially hindered rotation of the formylphenyl moiety, i.e., the occurrence of a conformational equilibrium has to be taken into account. Even the δHC−N 13C NMR signal remained under the noise level, indicating that the

Five-component, one-pot synthesis of an electroactive rotaxane comprising a bisferrocene macrocycle

• Natalie Lagesse,
• Luca Pisciottani,
• Maxime Douarre,
• Pascale Godard,
• Brice Kauffmann,
• Vicente Martí-Centelles and
• Nathan D. McClenaghan

Beilstein J. Org. Chem. 2020, 16, 1564–1571, doi:10.3762/bjoc.16.128

• macrocycle motion around the thread close to the coalescence temperature, in contrast with the other rotaxane proton signals, which had a peak width in the range of 2–5 Hz in the 300 MHz 1H NMR spectrum. A similar macrocycle pirouetting behaviour was observed in related 1-station [2]rotaxane systems [20]. An

Arylisoquinoline-derived organoboron dyes with a triaryl skeleton show dual fluorescence

• Vânia F. Pais,
• Tristan Neumann,
• Ignacio Vayá,
• M. Consuelo Jiménez,
• Abel Ros and
• Uwe Pischel

Beilstein J. Org. Chem. 2019, 15, 2612–2622, doi:10.3762/bjoc.15.254

• the syn and anti atropisomers because of the slow rotation around the chiral axis at this temperature. Free rotation around the C–C bond was observed at 80 °C and hence, variable-temperature 1H NMR studies showed coalescence of the signals to give an average spectrum (see Supporting Information File 1

• undertaken at 80 °C in C6D6 using a screw-cap NMR tube. Although significant changes were registered, a complete coalescence of the signals was not observed. The chiral HPLC analysis (see HPLC traces in Supporting Information File 1) demonstrated the high purity of compounds 16–19. The sharp peaks and

Calix[6]arene-based atropoisomeric pseudo[2]rotaxanes

• Carmine Gaeta,
• Carmen Talotta and
• Placido Neri

Beilstein J. Org. Chem. 2018, 14, 2112–2124, doi:10.3762/bjoc.14.186

• of 1 at 233 K clarified that this minor conformer was the cone one through the presence of an AX system at 3.35/4.42 ppm (COSY), which correlates with a carbon resonance at 29.1 ppm (HSQC), related to syn-oriented Ar rings (cone conformation). The coalescence temperature of the methylene protons was

• ascertained at 328 K in CDCl3; below this temperature the conformations of 1 were frozen, while at temperatures above 328 K the conformational interconversion is fast with respect to the NMR time scale (400 MHz). From the coalescence data we calculated a barrier of 14.6 kcal/mol for this process. In summary

Heterogeneous Pd catalysts as emulsifiers in Pickering emulsions for integrated multistep synthesis in flow chemistry

• Katharina Hiebler,
• Georg J. Lichtenegger,
• Manuel C. Maier,
• Eun Sung Park,
• Renie Gonzales-Groom,
• Bernard P. Binks and
• Heidrun Gruber-Woelfler

Beilstein J. Org. Chem. 2018, 14, 648–658, doi:10.3762/bjoc.14.52

• . Traditionally, emulsions have been kinetically stabilised by molecular species including surfactants, polymers or proteins all of which possess water-liking groups and oil-liking groups enabling them to adsorb to freshly created oil–water interfaces preventing to some extent coalescence between neighbouring

• droplets [25]. So-called Pickering emulsions, however, are stabilised solely by solid colloidal particles which can adsorb to droplet interfaces forming a protective layer endowing the emulsion with extremely high stability to coalescence [26]. Examples of suitable particles include silica, alumina, metals

• ). The stability of emulsions to gravity-induced creaming or coalescence was assessed by monitoring the position of the water–emulsion or oil–emulsion interfaces respectively. Microscopy images of the emulsions were recorded using an Olympus BX53 microscope with GXCAM-U318 camera attached and GXCapture-T

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

• (14.6 kcal/mol). The rate of rotation k at coalescence temperature can also be determined by applying the equation k = 2.22Δν, where Δν is the difference between resonance frequencies of the exchanging signals at slow exchange regime (at low temperature). The rotational barrier for compound 4c

Derivatives of the triaminoguanidinium ion, 5. Acylation of triaminoguanidines leading to symmetrical tris(acylamino)guanidines and mesoionic 1,2,4-triazolium-3-aminides

• Jan Szabo,
• Julian Greiner and
• Gerhard Maas

Beilstein J. Org. Chem. 2017, 13, 579–588, doi:10.3762/bjoc.13.57

• °C) was performed in the presence of air. Similar to structurally related guanidines (N-ureido instead of N-acyl substitution [3]) and to N,N’,N’’-tris(isopropylideneamino)guanidine [10], the 1H NMR signals of tris(acylamino)guanidines 6 are in coalescence over a wide temperature range, without

Correction: Synthesis, dynamic NMR characterization and XRD studies of novel N,N’-substituted piperazines for bioorthogonal labeling

• Constantin Mamat,
• Marc Pretze,
• Matthew Gott and
• Martin Köckerling

Beilstein J. Org. Chem. 2017, 13, 301–302, doi:10.3762/bjoc.13.32

• : building blocks; coalescence; dynamic NMR; labeling; Staudinger ligation; In the original article an incorrect caption for Figure 1 was given. The assignment of the solvents to the capital letters was not correct. The correct caption of Figure 1 is: 1H NMR spectra of compound 3a measured in five different

Thiazol-4-one derivatives from the reaction of monosubstituted thioureas with maleimides: structures and factors determining the selectivity and tautomeric equilibrium in solution

• Alena S. Pankova,
• Pavel R. Golubev,
• Alexander F. Khlebnikov,
• Alexander Yu. Ivanov and
• Mikhail A. Kuznetsov

Beilstein J. Org. Chem. 2016, 12, 2563–2569, doi:10.3762/bjoc.12.251

• it had been done earlier for 3a. On the other hand, heating the solution of thiazolidine 3g up to 120 °C led to coalescence. At this temperature even the signals of the ortho-protons of the 4-nitrophenyl ring (Δδ = 0.9 ppm at −20 °C) coalesced into one (Figure 2). The deviation of the tautomeric

Synthesis, dynamic NMR characterization and XRD studies of novel N,N’-substituted piperazines for bioorthogonal labeling

• Constantin Mamat,
• Marc Pretze,
• Matthew Gott and
• Martin Köckerling

Beilstein J. Org. Chem. 2016, 12, 2478–2489, doi:10.3762/bjoc.12.242

• observed for all nitro derivatives due to the limited change of the piperazine chair conformation. Therefore, two coalescence points were determined and their resulting activation energy barriers were calculated using 1H NMR. To support this result, single crystals of 1-(4-nitrobenzoyl)piperazine (3a

• applicability of these compounds as possible 18F-building blocks, two biomolecules were modified and chosen for conjugation either using the Huisgen-click reaction or the traceless Staudinger ligation. Keywords: building blocks; coalescence; dynamic NMR; labeling; Staudinger ligation; Introduction The

• temperature. Consequently, this phenomenon is strongly influenced by the substituent in the para-position of the benzoate (F vs NO2). Both effects resulted in two different coalescence points dependent upon their different energy barriers. In order to further investigate the conformational behavior of the

Synthesis and NMR studies of malonyl-linked glycoconjugates of N-(2-aminoethyl)glycine. Building blocks for the construction of combinatorial glycopeptide libraries

• Markus Nörrlinger,
• Sven Hafner and
• Thomas Ziegler

Beilstein J. Org. Chem. 2016, 12, 1939–1948, doi:10.3762/bjoc.12.183

• determine the coalescence temperature which resulted in calculated rotation barriers of 17.9–18.3 kcal/mol for the rotamers. Keywords: amino acids; carbohydrates; glycoconjugates; glycopeptides; N-(2-aminoethyl)glycine; Introduction The glycocalyx is a fringy or fuzzy polysaccharide layer coating most

• unambiguous assignment of the observed doublets to respective cis/trans rotameric forms could be achieved by 2D NMR spectroscopy. Since deuterochloroform is not suitable for temperature-dependent 1H NMR experiments at higher temperatures which, in turn, are necessary for determining the coalescence

• ppm area only) of 1a in the temperature range between 25 and 100 °C. Heating the sample caused a downfield shift of the anomeric amide protons with coalescence (Tc) at 90–95 °C (363–368 K). Unfortunately, the amide signals partially overlapped with the proton signals of the Fmoc group at the

Stereodynamic tetrahydrobiisoindole “NU-BIPHEP(O)”s: functionalization, rotational barriers and non-covalent interactions

• Golo Storch,
• Sebastian Pallmann,
• Frank Rominger and
• Oliver Trapp

Beilstein J. Org. Chem. 2016, 12, 1453–1458, doi:10.3762/bjoc.12.141

• barriers of stereodynamic ligands is crucial for the choice of conditions used for stereochemical alignment and subsequent application in catalysis. A rotational barrier of 92 kJ mol−1 for the unsubstituted BIPHEP was determined by NMR coalescence of a partially deuterated derivative [16]. However, this

Preparation of Pickering emulsions through interfacial adsorption by soft cyclodextrin nanogels

• Shintaro Kawano,
• Toshiyuki Kida,
• Mitsuru Akashi,
• Hirofumi Sato,
• Motohiro Shizuma and
• Daisuke Ono

Beilstein J. Org. Chem. 2015, 11, 2355–2364, doi:10.3762/bjoc.11.257

• that the Pickering emulsion becomes more stable. In a concentration range from 0.05 to 0.1 wt %, the change in the emulsion volume fractions is negligible for both oils, suggesting that 0.05 wt % concentration of the CD nanogel is sufficient to inhibit coalescence of the emulsions. Therefore, the mean

• the oil droplets from coalescence. Conclusion Amphiphilic CD nanogels, which are a new class of soft hydrogel nanoparticles, were prepared by crosslinking DM-β-CDs with PDI followed by the immersion in water. The DLS study shows that the primary CD nanogels (30–50 nm in diameter) assemble into larger

Conformational equilibrium in supramolecular chemistry: Dibutyltriuret case

• Karina Mroczyńska,
• Małgorzata Kaczorowska,
• Erkki Kolehmainen,
• Ireneusz Grubecki,
• Marek Pietrzak and
• Borys Ośmiałowski

Beilstein J. Org. Chem. 2015, 11, 2105–2116, doi:10.3762/bjoc.11.227

• intramolecular hydrogen bond we opt for argument "a". Figure 9 shows the changes in the spectra upon cooling (top spectrum represents +20 °C, spectra were recorded in 5° steps; the last spectrum at bottom represents a temperature of −70 °C). The coalescence temperature for complex 1∙∙∙10 is −15 °C. At

Ruthenium indenylidene “1^st generation” olefin metathesis catalysts containing triisopropyl phosphite

• Stefano Guidone,
• Fady Nahra,
• Alexandra M. Z. Slawin and
• Catherine S. J. Cazin

Beilstein J. Org. Chem. 2015, 11, 1520–1527, doi:10.3762/bjoc.11.166

• ). The 1H NMR spectrum of 1 in CD2Cl2 showed the typical indenylidene proton system (characteristic doublet at low field, δH = 8.80 ppm). Coalescence of the aliphatic protons assigned to the cyclohexyl and the phosphite moieties was also observed at room temperature. These signals were resolved at a

Microsolvation and sp²-stereoinversion of monomeric α-(2,6-di-tert-butylphenyl)vinyllithium as measured by NMR

• Rudolf Knorr,
• Monika Knittl and
• Eva C. Rossmann

Beilstein J. Org. Chem. 2014, 10, 2521–2530, doi:10.3762/bjoc.10.263

• ). Due to a kinetic trisolvation privilege of THF, the cis/trans sp2-stereoinversion rates could be measured through analyses of 1H NMR line broadening and coalescence only in THF as the solvent: The pseudomonomolecular (because THF-catalyzed), ionic mechanism is initialized by a C–Li bond heterolysis

• trans) through a “diastereotopomerization” [23] that interconverts the ground-state contact-ion pairs (CIP) 11 and 11' in Scheme 3. Increasing rates of this interchange will cause at first an increasing line broadening of the AB system and then a “coalescence” of all four lines into a singlet at the

• technique demands extrapolating the values of δcis – δtrans and 2JH,H from a series of low-temperature (less broadened) AB spectra into the coalescence domain. The temperature dependence of the resultant rate constants kψ (Table S1, [15]) is quantified in Figure 2 by a single straight line, which

Derivatives of the triaminoguanidinium ion, 3. Multiple N-functionalization of the triaminoguanidinium ion with isocyanates and isothiocyanates

• Jan Szabo,
• Kerstin Karger,
• Nicolas Bucher and
• Gerhard Maas

Beilstein J. Org. Chem. 2014, 10, 2255–2262, doi:10.3762/bjoc.10.234

• intermolecular NH hydrogen bonds), broad and partially overlapping signals and coalescence phenomena were observed. We were lucky, however, to obtain two spectra which clearly showed that the three branches of guandine 8 are magnetically non-equivalent: a) a 1H NMR spectrum taken in acetone-d6 at 290 K (see

Macrocyclic bis(ureas) as ligands for anion complexation

• Claudia Kretschmer,
• Gertrud Dittmann and
• Johannes Beck

Beilstein J. Org. Chem. 2014, 10, 1834–1839, doi:10.3762/bjoc.10.193

• amounts around 0.5 equivalents may be interpreted as a coalescence phenomenon caused by an exchange between loaded and unloaded host. After the amount of the anion reaches a molar ratio of 1:1, the N−H proton resonance of 2 shows no further increase in the shift, indicating that a 1:1 complex has been

Thermodynamically stable [4 + 2] cycloadducts of lanthanum-encapsulated endohedral metallofullerenes

• Yuta Takano,
• Yuki Nagashima,
• M. Ángeles Herranz,
• Nazario Martín and
• Takeshi Akasaka

Beilstein J. Org. Chem. 2014, 10, 714–721, doi:10.3762/bjoc.10.65

• did not show clear peaks at 290 K, distinct peaks were observed when the temperature was sufficiently lower or high enough distant from the coalescence temperature (Tc) (Figure 9). This fact suggests that the boat-to-boat inversions of 4a between the pentagon side and the hexagon side are sufficiently