Computational design for enantioselective CO₂ capture: asymmetric frustrated Lewis pairs in epoxide transformations

• Maxime Ferrer,
• Iñigo Iribarren,
• Tim Renningholtz,
• Ibon Alkorta and
• Cristina Trujillo

Beilstein J. Org. Chem. 2024, 20, 2668–2681, doi:10.3762/bjoc.20.224

• (keff). The definition given by Williams will be used (Equation 3, [42]): The proton affinity (PA) [43] of the LB and the fluoride ion affinity (FIA) [44] of the LA of a given FLP are generally used to rationalise the FLP reactivity observed [45][46]. Thus, PA and FIA of the different scaffolds

• centres are indicative of the FLP’s reactivity [45][46]. Thus, substituents must be selected to ensure a broad spectrum of acidity and basicity of the LA and LB. Different methods for determining these properties have been described in the literature. Because of their easy computation, the proton affinity

Aldiminium and 1,2,3-triazolium dithiocarboxylate zwitterions derived from cyclic (alkyl)(amino) and mesoionic carbenes

• Nedra Touj,
• François Mazars,
• Guillermo Zaragoza and
• Lionel Delaude

Beilstein J. Org. Chem. 2023, 19, 1947–1956, doi:10.3762/bjoc.19.145

• air and moisture, followed by an aqueous work-up. These results sharply contrasted with those obtained previously with a range of imidazolinium, benzimidazolium, or imidazolium salts, which were successfully converted into NHC·CS2 zwitterions under mild aerobic conditions [75]. Yet, the greater proton

• affinity and the higher basicity of CAACs and MICs vs NHCs [25][69][70][71] did not prevent the formation of the desired adducts using Cs2CO3 instead of KN(SiMe3)2 or NaOt-Bu, as evidenced by the appearance of revealing orange-red colors and by the emergence of a characteristic resonance for the CS2− unit

Effects of the aldehyde-derived ring substituent on the properties of two new bioinspired trimethoxybenzoylhydrazones: methyl vs nitro groups

• Dayanne Martins,
• Roberta Lamosa,
• Talis Uelisson da Silva,
• Carolina B. P. Ligiero,
• Sérgio de Paula Machado,
• Daphne S. Cukierman and
• Nicolás A. Rey

Beilstein J. Org. Chem. 2023, 19, 1713–1727, doi:10.3762/bjoc.19.125

• . In fact, the proton affinity (PA) of each hydrazone was calculated and the values suggest that hdz-NO2 has a higher tendency to be protonated in N1 than hdz-CH3 at about 2.40 kcal mol−1 (PA equal to −169.711 kcal mol−1 for the former and −167.316 kcal mol−1 for the latter), favoring the hydrolysis of

• susceptible to hydrolysis. This is also in conformity with the calculated proton affinity values for each compound, which indicate higher propensity towards hydrolysis for the nitro-derivative (−169.711 kcal mol−1) over the methyl-containing one (−167.316 kcal mol−1) when comparing their tendency to be

• that the obtained structures corresponded to energy minimums. The proton affinity (PA = EHL+ − EL) was calculated from the energy difference between each protonated molecule and the respective neutral molecule [65]. The Root Medium Square Difference (RMSD) between each experimental and theoretical

1,2,3,4-Tetrahydro-1,4,5,8-tetraazaanthracene revisited: properties and structural evidence of aromaticity loss

• Arnault Heynderickx,
• Sébastien Nénon,
• Olivier Siri,
• Vladimir Lokshin and
• Vladimir Khodorkovsky

Beilstein J. Org. Chem. 2019, 15, 2059–2068, doi:10.3762/bjoc.15.203

• predominantly the charge transfer type HOMO -> LUMO transitions (Supporting Information File 1, Tables S1 and S2). The easiness of protonation and stability of salts 6 evidenced the behavior of THTAA (3) as a strong base. Indeed, our DFT calculations of the proton affinity of THTAA (3) produced ΔH298 = 235.9

A simple and effective preparation of quercetin pentamethyl ether from quercetin

• Jin Tatsuzaki,
• Tomohiko Ohwada,
• Yuko Otani,
• Reiko Inagi and
• Tsutomu Ishikawa

Beilstein J. Org. Chem. 2018, 14, 3112–3121, doi:10.3762/bjoc.14.291

• reduced from that of the neural species (2B: −43.8°). In particular, 4'-anion 2B and 5-anion 2B are affected by conjugation between the chromenone moiety and the phenyl group (biaryl dihedral angle: −29.6° in 4'-anion 2B; −29.6° in 5-anion 2B). Change of proton affinity during the methylation reaction

A novel synthetic approach to hydroimidazo[1,5-b]pyridazines by the recyclization of itaconimides and HPLC–HRMS monitoring of the reaction pathway

• Dmitry Yu. Vandyshev,
• Khidmet S. Shikhaliev,
• Andrey Yu. Potapov,
• Michael Yu. Krysin,
• Fedor I. Zubkov and
• Lyudmila V. Sapronova

Beilstein J. Org. Chem. 2017, 13, 2561–2568, doi:10.3762/bjoc.13.252

• observed, whose peak is identified by the retention time (4.13 min) determined for the pure substance. The long retention time (5.6 min) and the insignificant content (less than 1%) of the initial itaconimide 1d found under ESI conditions in the reaction mixture are due to its extremely low proton affinity

Proton transfers in the Strecker reaction revealed by DFT calculations

• Shinichi Yamabe,
• Guixiang Zeng,
• Wei Guan and
• Shigeyoshi Sakaki

Beilstein J. Org. Chem. 2014, 10, 1765–1774, doi:10.3762/bjoc.10.184

• )-CNH+ R-CH(NH2)-CNH+ + OH2 → R-CH(NH2)-C(OH)=NH + H+ However, the proton affinity (PA) of the nitrile is much smaller than that of the amino group, for example, the PAs of the cyano and amino groups of 2-amino-propanonitrile (Me-CH(NH2)-CN) are 190.7 and 199.6 kcal/mol, respectively. Thus, in the

Substrate dependent reaction channels of the Wolff–Kishner reduction reaction: A theoretical study

• Shinichi Yamabe,
• Guixiang Zeng,
• Wei Guan and
• Shigeyoshi Sakaki

Beilstein J. Org. Chem. 2014, 10, 259–270, doi:10.3762/bjoc.10.21

• be taken. However, the HO-t-Bu species formed by elimination (TS6) is far from the para positions of the phenyl rings. In addition, the anion character in the carbanion is delocalized, which leads to the low proton affinity of the para carbon atoms. Thus, in the aprotic solvent the carbanion center

One-pot tandem cyclization of enantiopure asymmetric cis-2,5-disubstituted pyrrolidines: Facile access to chiral 10-heteroazatriquinanes

• Ping-An Wang,
• Sheng-Yong Zhang and
• Henri B. Kagan

Beilstein J. Org. Chem. 2013, 9, 265–269, doi:10.3762/bjoc.9.32

• -ray structure of 1·HBF4 revealed that the centro-N is pyramidalized. 10-azatriquinacene (2), an unsaturated analogue of 1, was attractive due to its high proton affinity [7]. Recently, Mascal [8] and colleagues have developed a series of 10-azatriquinanes as a C3v-symmetric platform for tripodal metal

Theoretical study on β-cyclodextrin inclusion complexes with propiconazole and protonated propiconazole

• Adrian Fifere,
• Narcisa Marangoci,
• Stelian Maier,
• Adina Coroaba,
• Dan Maftei and
• Mariana Pinteala

Beilstein J. Org. Chem. 2012, 8, 2191–2201, doi:10.3762/bjoc.8.247

• the positively charged guest molecule, a model of PPH+ was built. The proton affinity (PA) was calculated for each of the five protonation sites of the azole ring (according to the notation scheme shown in Figure 1b). According to reference [21][22], PA was defined as the energy variation in the

• been removed. Molecular parameters of the most stable β-CD/PP inclusion compounds in both A and B configurations, as given by AM1 and PM3 calculations and by B3LYP/6-31G(d)+ single-point calculations applied on the PM3 optimized geometries. The calculated values of the proton affinity of the denoted

A quantitative approach to nucleophilic organocatalysis

• Herbert Mayr,
• Sami Lakhdar,
• Biplab Maji and
• Armin R. Ofial

Beilstein J. Org. Chem. 2012, 8, 1458–1478, doi:10.3762/bjoc.8.166

• character (NICS(1)). However, while the electrophilic addition to the exocyclic double bond of 47a yields the cyclic conjugated 6π system in 48a, the analogous electrophilic addition to 47c yields the nonaromatic amidinium ion 48c. The high nucleophilicity of 45a, which is mirrored by the high proton

• affinity of 47a, can thus be explained by the gain of aromaticity during electrophilic attack. The same line of arguments can be used to rationalize the higher nucleophilicities and basicities of the triazoline derivatives 45b and 47b, respectively [107]. As the unsaturated carbenes 49a and 49b have

Cation affinity numbers of Lewis bases

• Christoph Lindner,
• Raman Tandon,
• Boris Maryasin,
• Evgeny Larionov and
• Hendrik Zipse

Beilstein J. Org. Chem. 2012, 8, 1406–1442, doi:10.3762/bjoc.8.163

• substrate model for acyl-transfer reactions. Affinities towards these cationic electrophiles are complemented by data for Lewis-base addition to Michael acceptors as prototypical neutral electrophiles. Keywords: ab initio; cation affinity; Lewis basicity; organocatalysis; proton affinity; Introduction

• Cation affinity values are important guidelines for the reactivity of Lewis and Brønstedt bases [1][2][3]. While proton affinity numbers (either as gas phase proton affinities or as solution phase pKa values) have been used for a long time in quantitative approaches to describe base-induced or base

Volatile organic compounds produced by the phytopathogenic bacterium Xanthomonas campestris pv. vesicatoria 85-10

• Teresa Weise,
• Marco Kai,
• Anja Gummesson,
• Armin Troeger,
• Stephan von Reuß,
• Silvia Piepenborn,
• Francine Kosterka,
• Martin Sklorz,
• Ralf Zimmermann,
• Wittko Francke and
• Birgit Piechulla

Beilstein J. Org. Chem. 2012, 8, 579–596, doi:10.3762/bjoc.8.65

• range between 30 and 250 with signals that were significantly enhanced (5% confidence level) compared to those of the blank control samples. If the proton affinity of an analyte molecule is higher than the one of H3O+ the proton transfer reaction is more or less quantitative (quasi-first-order reaction

• investigated more comprehensively. In addition, inorganic compounds have to be considered, including hydrogen cyanide (HCN) and ammonia. HCN is produced, e.g., by Pseudomonas spp. [55] and, due to its slightly higher proton affinity than water, it should be detectable down to a concentration lower than 100 ppb

• , structure assignments are based on comparison with GC/MS data (i.e., as performed also in this work) and literature-based information. Selectivity may be enhanced by using ammonia as the primary ion-source gas. Ammonia has a higher proton affinity than water, and therefore, some substance classes can be

Enantioselective supramolecular devices in the gas phase. Resorcin[4]arene as a model system

• Caterina Fraschetti,
• Matthias C. Letzel,
• Antonello Filippi,
• Maurizio Speranza and
• Jochen Mattay

Beilstein J. Org. Chem. 2012, 8, 539–550, doi:10.3762/bjoc.8.62

• homologues, with the exception of the [C∙H∙G]+ complexes with G = A4, N2, N4 (Table 5) [58]. As previously mentioned, the origin of the enantioselectivities showed in Table 5 can be due to a thermodynamic and/or kinetic control of the reaction coordinates. It has been found that when the proton affinity of

• similar to the starting diastereomeric reactant complexes, by following the proton affinity order of B. This interpretation was supported by independent MS tandem measurements carried out on the [CM,Ra∙CP,Sb∙H∙G]+ (G = N1; N2; a,b = H,D or D,H) ternary adducts yielding [CM,Ra∙H∙G]+ and [CP,Sb∙H∙G]+ as the

• of ρ on the proton affinity of the amine and the independent CID data clearly indicates that the kinetics of the [C∙H∙N1]+ adducts is mostly controlled by the cyclochirality determining the differential energies of the involved transition structures. In contrast, the significant enantioselectivity

Intramolecular hydroxycarbene C–H-insertion: The curious case of (o-methoxyphenyl)hydroxycarbene

• Dennis Gerbig,
• David Ley,
• Hans Peter Reisenauer and
• Peter R. Schreiner

Beilstein J. Org. Chem. 2010, 6, 1061–1069, doi:10.3762/bjoc.6.121

• an acid-catalyzed formation of the aldehyde, is presented in Scheme 9: Protonation of 5 at the carbene center by 6 leads to a carbonyl-protonated aldehyde [7+H]+, which is then deprotonated at the oxygen atom in the follow-up reaction, regenerating 6 and producing 7. As the proton affinity Epa of 5