Substituent effect on the energy barrier for σ-bond formation from π-single-bonded species, singlet 2,2-dialkoxycyclopentane-1,3-diyls

• Jianhuai Ye,
• Yoshihisa Fujiwara and
• Manabu Abe

Beilstein J. Org. Chem. 2013, 9, 925–933, doi:10.3762/bjoc.9.106

• entropy effect were found to play crucial roles in increasing the lifetime. Keywords: laser flash photolysis; lifetime; singlet diradicals (biradicals); substituent effect; π-single bond; Introduction Localized singlet diradicals are key intermediates in processes involving the homolytic bond-cleavage

• , entry 4) with that of DRd (1933 ns, Table 1, entry 3). When the 3,5-dimethoxyphenyl group was introduced at all of the C(1), C(2), and C(3) positions, the lifetime of the diradical DRf (ΔG‡ = 42.2 kJ mol−1, Table 1, entry 5) was dramatically increased to 5394 ns at 293 K. The activation entropy (ΔS

• lifetimes are largely dependent on the substituent pattern of Ar and Ar’ at the C(1)–C(3) positions of the 1,3-diyls. Thus, both the enthalpy and entropy effect were found to play crucial roles in increasing the lifetime. Experimental All reagents were purchased from commercial sources and were used without

Kinetics and mechanism of the anilinolysis of aryl phenyl isothiocyanophosphates in acetonitrile

• Hasi Rani Barai and
• Hai Whang Lee

Beilstein J. Org. Chem. 2013, 9, 615–620, doi:10.3762/bjoc.9.68

• . Activation parameters, enthalpies and entropies of activation, are determined as shown in Table 5. The enthalpies of activation are relatively low and entropies of activation are of relatively large negative value. The relatively low value of activation enthalpy and large negative value of activation entropy

Complete σ* intramolecular aromatic hydroxylation mechanism through O₂ activation by a Schiff base macrocyclic dicopper(I) complex

• Albert Poater and
• Miquel Solà

Beilstein J. Org. Chem. 2013, 9, 585–593, doi:10.3762/bjoc.9.63

• same solvent used experimentally. The relative Gibbs energies reported in this work include energies computed using the B3LYP/6-311G(d,p)//B3LYP/6-31G(d) method together with solvent effects obtained at the B3LYP/6-31G(d) level, and zero-point energies, thermal corrections, and entropy effects

Electron and hydrogen self-exchange of free radicals of sterically hindered tertiary aliphatic amines investigated by photo-CIDNP

• Martin Goez,
• Isabell Frisch and
• Ingo Sartorius

Beilstein J. Org. Chem. 2013, 9, 437–446, doi:10.3762/bjoc.9.46

• -sensitized reaction lends a posteriori support to our above reasoning. From the regression lines in Figure 4, one calculates the activation parameters given in Table 2. The much more negative activation entropy in the XA-sensitized reaction is clearly consistent with our preceding explanation of the

• different reaction rates, because a hydrogen self-exchange must involve a more ordered transition state than an electron self-exchange; the small positive activation entropy in the AQ-sensitized reaction also supports our interpretation, because this is a well-known fact for outer-sphere electron transfer

Asymmetric Diels–Alder reaction with >C=P– functionality of the 2-phosphaindolizine-η¹-P-aluminium(O-menthoxy) dichloride complex: experimental and theoretical results

• Rajendra K. Jangid,
• Nidhi Sogani,
• Neelima Gupta,
• Raj K. Bansal,
• Moritz von Hopffgarten and
• Gernot Frenking

Beilstein J. Org. Chem. 2013, 9, 392–400, doi:10.3762/bjoc.9.40

• unaffected in methylene chloride. Kinetics of the reactions Standard-state entropies and entropy changes of different species, as well as the enthalpies and the Gibbs free energies of the computed reactions (as shown in Scheme 5) are given in Table 1. The entropy effects have been found to play a major role

• in enzyme catalysis [53]. However, in the present case, the entropy difference between the TS1 and TS3 is negligible and does not appear to play significant role. On the other hand, entropy effects favour the endo approach over the exo approach from the Si face. Although the three reactions are

• -phosphaindolizine complex. Standard state entropies S0, entropy change ΔS, reaction enthalpies ΔH0 and reaction Gibbs free energies ΔG0. Supporting Information Supporting Information File 142: Cartesian coordinates of the geometries optimized (Table S1) and total energies of reactants, transition structures and

Spin state switching in iron coordination compounds

• Philipp Gütlich,
• Ana B. Gaspar and
• Yann Garcia

Beilstein J. Org. Chem. 2013, 9, 342–391, doi:10.3762/bjoc.9.39

• τN, and thus, the spin state fluctuation rate is 1/τN ≤ 107 s−1. Calorimetry Studies of SCO compounds often require a knowledge of thermodynamic quanitities such as the changes of enthalpy ΔH = HHS − HLS and entropy ΔS = SHS − SLS because of their valuable information regarding the ST properties, in

• particular cooperative interactions and the order of the ST transition. Enthalpy changes ΔH = HHS − HLS are typically 10 to 20 kJ mol−1, and entropy changes ΔS = SHS − SLS are on the order of 50 to 80 J mol−1 K−1 [22]. The thermally induced ST is an entropy-driven process because the degree of freedom is

• much higher in the HS state than in the LS state, which is schematically shown in Figure 1 by the narrower distances between the vibrational levels in the HS state as compared to the LS state. Approximately 25% of the total entropy gain on going from LS to HS is of magnetic origin, viz., it arises from

Towards a biocompatible artificial lung: Covalent functionalization of poly(4-methylpent-1-ene) (TPX) with cRGD pentapeptide

• Lena Möller,
• Christian Hess,
• Jiří Paleček,
• Yi Su,
• Axel Haverich,
• Andreas Kirschning and
• Gerald Dräger

Beilstein J. Org. Chem. 2013, 9, 270–277, doi:10.3762/bjoc.9.33

• hydrophilicity resulting from the oxidative plasma conditioning on the surface [32]. The plasma-mediated surface oxidation yields polar groups including hydroxy groups, which rapidly vanish, a well-investigated aging effect of plasma-treated materials. This process is an entropy-initiated surface reorientation

Preparation of mixed trialkyl alkylcarbonate derivatives of etidronic acid via an unusual route

• Petri A. Turhanen,
• Janne Weisell and
• Jouko J. Vepsäläinen

Beilstein J. Org. Chem. 2012, 8, 2019–2024, doi:10.3762/bjoc.8.228

• chloride as the reagent [30], or more probably after rearrangement by means of a regular acid (HCl) hydrolysis. The driving force in this irreversible reaction is entropy, since gaseous CH3Cl is evaporated leading to product 2. The formation of the stable intermediate 2 also explains the difficulty

Influence of intramolecular hydrogen bonds on the binding potential of methylated β-cyclodextrin derivatives

• Gerhard Wenz

Beilstein J. Org. Chem. 2012, 8, 1890–1895, doi:10.3762/bjoc.8.218

• β-CD 3 and the 2,3-dimethylated derivative 6 showed the lowest binding constants K, less than one tenth of the one of native β-CD 1. These very low binding constants are accompanied by positive values of the entropy term −TΔS° weakening the binding free enthalpy ΔG°. On the other hand, binding

• secondary positions showed much lower affinities towards this guest than 1 did. Again, a positive value of the entropy term −TΔS° was found for 2,3,5-tri-O-methyl-β-CD. As shown in Figure 2, this entropy term further grew with increasing temperature, compensating most of the strongly negative binding

• of neutral guests by concave hosts in water, because it can lead both to entropy gains and enthalpic advantages [36]. The observed value for 2,3,5-tri-O-methyl-β-CD is even higher than that for native β-CD, ΔCp = −320 ± 20 J mol−1 K−1 [37]. This difference was attributed to the larger internal

The preferred conformation of erythro- and threo-1,2-difluorocyclododecanes

• Yi Wang,
• Peer Kirsch,
• Tomas Lebl,
• Alexandra M. Z. Slawin and
• David O'Hagan

Beilstein J. Org. Chem. 2012, 8, 1271–1278, doi:10.3762/bjoc.8.143

• ground state, thus this is most probably the major contributor to the enthalpy difference. The opposite sign in entropy (ΔS#) for each isomer makes a relatively small contribution to the overall free energy; however, the positive value for the erythro isomer is perhaps unexpected for progression towards

An intramolecular inverse electron demand Diels–Alder approach to annulated α-carbolines

• Zhiyuan Ma,
• Feng Ni,
• Grace H. C. Woo,
• Sie-Mun Lo,
• Philip M. Roveto,
• Scott E. Schaus and
• John K. Snyder

Beilstein J. Org. Chem. 2012, 8, 829–840, doi:10.3762/bjoc.8.93

• annulations was previously noted by Taylor [95][96][97][98], and has been ascribed to the greater entropy loss for the larger rings [99]. Indeed, it has been estimated that the effective molarity for 5-membered ring closures can be as high as 1,000-fold greater in comparison to 6-membered ring cyclizations

Self-assembly of Ru₄ and Ru₈ assemblies by coordination using organometallic Ru(II)₂ precursors: Synthesis, characterization and properties

• Sankarasekaran Shanmugaraju,
• Dipak Samanta and
• Partha Sarathi Mukherjee

Beilstein J. Org. Chem. 2012, 8, 313–322, doi:10.3762/bjoc.8.34

• the loss of entropy in the latter case is more. As shown in Scheme 2, the binuclear acceptor 1a or 1b was treated separately with an imidazole-based tetratopic donor L in a 2:1 molar ratio in methanol at room temperature to obtain [2 + 1] self-assembled macrocycles 2a and 2b, respectively, in high

Synthesis of multivalent host and guest molecules for the construction of multithreaded diamide pseudorotaxanes

• Nora L. Löw,
• Egor V. Dzyuba,
• Boris Brusilowskij,
• Lena Kaufmann,
• Elisa Franzmann,
• Wolfgang Maison,
• Emily Brandt,
• Daniel Aicher,
• Arno Wiehe and
• Christoph A. Schalley

Beilstein J. Org. Chem. 2012, 8, 234–245, doi:10.3762/bjoc.8.24

• view of previous theoretical calculations on amide/tetralactam macrocycle complexes [111], which show that simple amide axles dethread in the gas phase because of a favourable entropy term arising from the increase in particle number upon complex dissociation. This entropic contribution overcompensates

Thermodynamic and kinetic stabilization of divanadate in the monovanadate/divanadate equilibrium using a Zn-cyclene derivative: Towards a simple ATP synthase model

• Hanno Sell,
• Anika Gehl,
• Frank D. Sönnichsen and
• Rainer Herges

Beilstein J. Org. Chem. 2012, 8, 81–89, doi:10.3762/bjoc.8.8

• complexed monovanadate is only possible from the non-shielded side. Moreover, the role of the monovanadate acting as the electrophile is defined by complexation which reduces the probability of effective collisions and, thus, decreases the entropy of activation. Both effects, obviously, overcompensate the

(How) does 1,3,5-triethylbenzene scaffolding work? Analyzing the abilities of 1,3,5-triethylbenzene- and 1,3,5-trimethylbenzene-based scaffolds to preorganize the binding elements of supramolecular hosts and to improve binding of targets

• Xing Wang and
• Fraser Hof

Beilstein J. Org. Chem. 2012, 8, 1–10, doi:10.3762/bjoc.8.1

• methyl groups, but the size of this advantage can be small and is dependent on the groups involved. Keywords: binding affinity; entropy; molecular recognition; scaffolds; supramolecular hosts; triethylbenzene; trimethylbenzene; Introduction Supramolecular hosts use arrays of multiple weak interactions

• the energy that must be paid to adopt a (potentially unfavorable) binding conformation, and can also have effects on binding entropy when one considers the degrees of freedom in the host, guest, and solvated host–guest complex. Rigid macrocyclic hosts are often successful because of their high degree

• ) calculated here are most closely akin to enthalpies (∆H), and neglect differences in entropy (∆S) from one host type to another. The aspects of host entropy that might contribute to guest binding, i.e., translational, vibrational, solvation, and configurational entropy, are worth separate discussions

Dependency of the regio- and stereoselectivity of intramolecular, ring-closing glycosylations upon the ring size

• Patrick Claude,
• Christian Lehmann and
• Thomas Ziegler

Beilstein J. Org. Chem. 2011, 7, 1609–1619, doi:10.3762/bjoc.7.189

• , entropy-reducing intramolecular cyclization step. Within the frame of an overall SN1 reaction, the cyclization step is regarded as the rate-determining step; therefore, the transition state for the nucleophilic addition to the glycosyl cyclic oxonium intermediate may allow for a rationalization of the

Intramolecular hydroamination of alkynic sulfonamides catalyzed by a gold–triethynylphosphine complex: Construction of azepine frameworks by 7-exo-dig cyclization

• Hideto Ito,
• Tomoya Harada,
• Hirohisa Ohmiya and
• Masaya Sawamura

Beilstein J. Org. Chem. 2011, 7, 951–959, doi:10.3762/bjoc.7.106

• alkyne substrates, which had also been difficult due to the steric repulsion between a nucleophilic center and a terminal substituent on the alkyne moiety [56]. We proposed that the cavity in the ligand forces the nucleophilic center closer to the gold-bound alkyne, resulting in the entropy-based rate

• , gold-catalyzed hydroamination of N-(5-hexyn-1-yl)-p-toluenesulfonamide 7. As expected from entropy considerations, the six-membered ring formations of 7 with these ligands were generally much faster than the seven-membered ring formations of 4: The reaction with 0.5 mol % catalyst loading at room

Kinetic evaluation of the solvolysis of isobutyl chloro- and chlorothioformate esters

• Malcolm J. D’Souza,
• Matthew J. McAneny,
• Dennis N. Kevill,
• Jin Burm Kyong and
• Song Hee Choi

Beilstein J. Org. Chem. 2011, 7, 543–552, doi:10.3762/bjoc.7.62

• organic mixtures with wide ranging nucleophilicity and ionizing power. For 1, we also report the first-order rate constants determined at different temperatures in pure ethanol (EtOH), methanol (MeOH), 80% EtOH, and in both 97% and 70% 2,2,2-trifluoroethanol (TFE). The enthalpy (ΔH≠) and entropy (ΔS≠) of

• corresponding values of the enthalpy (ΔH≠) and entropy (ΔS≠) of activation. Results and Discussion The specific rates of solvolysis of 1 at 40.0 °C and of 2 at 25.0 °C, are reported in Table 1. Also presented in Table 1 are the NT and YCl values needed for the multiple correlation analysis of the assembled data

• using Equation 1. For 1, we report in Table 2 the first-order rate constants determined at different temperatures in pure ethanol (EtOH), methanol (MeOH), 80% EtOH, 97% 2,2,2-trifluoroethanol (TFE) and 70% TFE. The corresponding enthalpy (ΔH≠) and entropy (ΔS≠) of activation values obtained from

Heavy atom effects in the Paternò–Büchi reaction of pyrimidine derivatives with 4,4’-disubstituted benzophenones

• Feng-Feng Kong,
• Jian-Bo Wang and
• Qin-Hua Song

Beilstein J. Org. Chem. 2011, 7, 113–118, doi:10.3762/bjoc.7.16

• 1b. Temperature effects on the regioselectivity of 1b–e systems showed some interesting features for systems with heavy atoms (including the 1d and 1e systems), such as higher inversion temperatures, and an entropy-controlled regioselectively whereas the regioselectivity for two other systems (1b and

• 1c) is enthalpy–entropy controlled. A heavy atom effect is suggested to be responsible for these unusual phenomena based on the triplet-diradical mechanism of the Paternò–Büchi reaction. Keywords: benzophenone; heavy atom effect; Paternò–Büchi reaction; regioselectivity; triplet diradical

• other systems (−2.1 J/mol for 1d, −3.2 kJ/mol for 1e). In other words, this is an entropy-determined selection for the regioselectivity over the whole temperature range investigated. Interception of heavy atom effects Based on the triplet mechanism of the Paternò–Büchi reaction, it is possible to have a

The intriguing modeling of cis–trans selectivity in ruthenium-catalyzed olefin metathesis

• Naeimeh Bahri-Laleh,
• Raffaele Credendino and
• Luigi Cavallo

Beilstein J. Org. Chem. 2011, 7, 40–45, doi:10.3762/bjoc.7.7

• kcal·mol−1, since the gas-phase rotational/translational entropy of coordination from classical statistical thermodynamics is generally considered to overestimate the coordination entropy in solution. The –TΔS contribution of 10 kcal·mol−1 is the experimental coordination entropy of C2H4 to a Pd-complex

Gelation or molecular recognition; is the bis-(α,β-dihydroxy ester)s motif an omnigelator?

• Peter C. Griffiths,
• David W. Knight,
• Ian R. Morgan,
• Amy Ford,
• James Brown,
• Ben Davies,
• Richard K. Heenan,
• Stephen M. King,
• Robert M. Dalgliesh,
• John Tomkinson,
• Stuart Prescott,
• Ralf Schweins and
• Alison Paul

Beilstein J. Org. Chem. 2010, 6, 1079–1088, doi:10.3762/bjoc.6.123

• [35], in which the gelation character was found to depend on both solvent composition and the molecular structure of the gelator. The enthalpy of melting ΔHm for a series of gelators was found to be positive, indicating an endothermic melting process, associated with the increase in entropy

Kinetics and mechanism of vanadium catalysed asymmetric cyanohydrin synthesis in propylene carbonate

• Michael North and
• Marta Omedes-Pujol

Beilstein J. Org. Chem. 2010, 6, 1043–1055, doi:10.3762/bjoc.6.119

• temperatures between 253 and 293 K. The resulting rate data are presented in Table 4. The corresponding Eyring plot is shown in Figure 4. The Eyring equation (Equation 2) relates the rate constant for a reaction to the enthalpy and entropy of activation. Replacing the actual rate constant in Equation 2 with

• k2obs (k2obs = k2[2]x) and rearranging gives Equation 3, which, after taking the logarithm of both sides, gives Equation 4. The enthalpy of activation (ΔH‡) can then be obtained from the slope of the best-fit line from the data plotted in Figure 4 and was found to be 67.8 (±0.2) kJ mol−1. The entropy of

• present in propylene carbonate, whilst both reaction components are activated and pre-organized for reaction by the binuclear, catalytically active species present in dichloromethane [28]. The less negative value for the entropy of activation in propylene carbonate compared to that determined in

Novel tetracyclic structures from the synthesis of thiolactone-isatin hybrids

• Renate Hazel Hans,
• Hong Su and
• Kelly Chibale

Beilstein J. Org. Chem. 2010, 6, No. 78, doi:10.3762/bjoc.6.78

• ′-substituted tetracycles (Table 1 and Table 2). This drawback can most likely be ascribed to entropy factors and stereoelectronic effects [45][46][47][48]. The structures of the tetracycles 4 were unambiguously assigned by single crystal X-ray crystallographic analysis. Single crystals for 4a–c were obtained

RAFT polymers for protein recognition

• Alan F. Tominey,
• Julia Liese,
• Sun Wei,
• Klaus Kowski,
• Thomas Schrader and
• Arno Kraft

Beilstein J. Org. Chem. 2010, 6, No. 66, doi:10.3762/bjoc.6.66

• pattern to a carboxylate, so that similar affinities would have been expected. Most likely, the difference is explained by interactions with the π-face of the tetrazolate anion, which are not possible with a carboxylate. In all cases, protein complexation by RAFT polymers was endothermic, i.e., entropy

• substantially by 1–2 orders of magnitude (see Table 1: T20 vs T20CH15). In other words, the random incorporation of cyclohexyl comonomers into the polymer was beneficial for the protein recognition event. Close inspection of thermodynamic data revealed that the entropy term was responsible for this increased

• some cases reaching micromolar or sub-micromolar Kd values. Copolymerization with N-cyclohexylacrylamide introduced additional nonpolar groups beneficial for protein binding, leading to a substantial entropy gain and significantly improving protein affinities. The best pair was a bisphosphonate

Molecular recognition of organic ammonium ions in solution using synthetic receptors

• Andreas Späth and
• Burkhard König

Beilstein J. Org. Chem. 2010, 6, No. 32, doi:10.3762/bjoc.6.32

• coulombic interactions are around 8 kJ/mol [15]. In aqueous medium ion pair formation is primarily driven by entropy, not directly by coulombic forces [16]. The binding energy is, in general, independent of the geometry, polarizability of the ions or the formation of a salt bridge. In addition, the

• increase in molecular rigidity by introducing a second macrocyclic ring in the monocyclic pyridino crown ligand. Positive values of entropy changes for 18-NEA interactions, as compared to 19-NEA interactions (which show negative values of entropy changes) suggest a smaller conformational change of ligand