Alkene selenenylation: A comprehensive analysis of relative reactivities, stereochemistry and asymmetric induction, and their comparisons with sulfenylation

• Vadim A. Soloshonok and
• Donna J. Nelson

Beilstein J. Org. Chem. 2011, 7, 744–758, doi:10.3762/bjoc.7.85

• magnitude greater (Table 1, entries 20 versus 21, or 26 versus 27). 3. Alkyl branching α to C=C: The data obtained in this study pointed to a new steric effect in linear free energy relationships, which can be defined as alkyl group α-branching. Thus, within each line fit, there is a clear trend dependent

Gold-catalyzed heterocyclizations in alkynyl- and allenyl-β-lactams

• Benito Alcaide and
• Pedro Almendros

Beilstein J. Org. Chem. 2011, 7, 622–630, doi:10.3762/bjoc.7.73

• (DFT) calculations were performed to obtain insight on various aspects of this reactivity and indicated the selective activation of the allene and alkyne component. Free energy profile [kcal mol–1] for the transformation of γ-allenol I into the tetrahydrofuran type 9. Gold-catalyzed cyclization of 4

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

• activation values obtained from Arrhenius plots for 1 in these five solvents are reported. The specific rates of solvolysis were analyzed using the extended Grunwald–Winstein equation. Results obtained from correlation analysis using this linear free energy relationship (LFER) reinforce our previous

The arene–alkene photocycloaddition

• Ursula Streit and
• Christian G. Bochet

Beilstein J. Org. Chem. 2011, 7, 525–542, doi:10.3762/bjoc.7.61

• (simplified) Weller equation determines whether or not electron transfer will occur from an excited-state (Equation 1) [24][25]. For the reaction of an excited aromatic moiety with an alkene, this means that if the change in free energy, determined by the Weller equation, is negative. with ΔGET = free

Accuracy in determining interproton distances using Nuclear Overhauser Effect data from a flexible molecule

• Catharine R. Jones,
• Craig P. Butts and
• Jeremy N. Harvey

Beilstein J. Org. Chem. 2011, 7, 145–150, doi:10.3762/bjoc.7.20

• (vide supra) for each conformer by a range of populations (x) of 1a/b. The best fit to experiment is obtained at ~55% 1a/b, (and thus ~45% 2a/b), corresponding to a free energy difference of ca. 2.1–2.2 kJ/mol between conformers 1a/b and 2a/b. This compares extremely well with the highest level

• calculations, which suggest a corresponding free energy difference of ca. 1.5 kJ/mol. This remarkable match in populations and energies supports the proposition that fitting populations of conformers from the NOE-derived distances is an inherently accurate approach when the geometries of the contributing

Synthesis of Ru alkylidene complexes

• Renat Kadyrov and
• Anna Rosiak

Beilstein J. Org. Chem. 2011, 7, 104–110, doi:10.3762/bjoc.7.14

• these data gave activation enthalpy ΔH≠= 13.7 kcal/mol. From the rate constant at 303 K the value of free energy of activation (ΔG≠303K = 12.6 kcal/mol) was also calculated. This is substantially higher than several calculated (Ea = 4.4 kcal/mol) [11][12] and experimentally estimated (Ea = 5.7 kcal/mol

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

• metathesis with the Ru–propylidene moiety, or propene reactivity with the Ru–methylidene moiety, which would be the other Ru–alkylidene bonds present in the reaction mixture after complete activation of the starting precatalyst, are not considered. Results and Discussion The free energy profile in CH2Cl2 for

• into the most stable metallacycle. For this reason, the energy profile of Figure 1 suggests that the most likely event from Co2-cis and Co2-trans is not product release, but rather their transformation into MCy2-cis and MCy2-trans. The escape from Co2-cis and Co2-trans is controlled by the free energy

Stereoselectivity of supported alkene metathesis catalysts: a goal and a tool to characterize active sites

• Christophe Copéret

Beilstein J. Org. Chem. 2011, 7, 13–21, doi:10.3762/bjoc.7.3

• most acyclic alkenes) has a free energy close to 0 and is reversible, the (E/Z) ratio readily evolves towards a thermodynamic value [(E/Z) ≥ 3 for di-substituted alkenes] via metathesis, and all the valuable kinetic stereochemical information is easily lost, and consequently special care has to be

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

• energies of activation (ΔG‡) at 273 K are similar at 53.1 and 57.5 kJ mol−1 for reactions carried out in propylene carbonate and dichloromethane, respectively. (kB = Boltzmann’s constant, h = Planck’s constant, R = gas constant) Since differences in the Gibbs free energy of activation could not account for

Catalysis: transition-state molecular recognition?

• Ian H. Williams

Beilstein J. Org. Chem. 2010, 6, 1026–1034, doi:10.3762/bjoc.6.117

• concept. It is shown that reactant binding is intrinsically inhibitory, and that attempts to design catalysts that focus simply upon attractive interactions in a binding site may fail. Free-energy changes along the reaction coordinate for SN2 methyl transfer catalysed by the enzyme catechol-O-methyl

• ) boat conformation and in which a single-atom mutation affects the free-energy of activation dramatically. Keywords: catalysis; computational simulation; enzymes; molecular recognition; transition state; Introduction “Molecular recognition of transition states” was the title of a paper presented by

• free energy surface) and a transition structure (corresponding to a saddle point on a potential energy surface). The commonly assumed identity between the two terms is often reasonable for small, “simple” systems in vacuum, for which it may be sufficient to model the TS by first finding a transition

Symmetry breaking and structure of a mixture of nematic liquid crystals and anisotropic nanoparticles

• Marjan Krasna,
• Matej Cvetko and
• Milan Ambrožič

Beilstein J. Org. Chem. 2010, 6, No. 74, doi:10.3762/bjoc.6.74

• magnetic field towards the perpendicular direction. Here we assume that originates from magnetic NPs, where μ0 is the magnetic permittivity constant and represents the magnetization of NPs due to the magnetic dipole moment . The resulting quadrupolar magnetic field free energy density change ΔfB is

• approximately given by where Δχ is the magnetic anisotropy of LC molecules [6] (which can be either positive or negative). Furthermore, introducing an elongated NP of length d into a LC, which via surface anchoring enforces elastic distortion in LC medium, typically gives rise to free energy penalties of the

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

• affinity. We therefore tentatively explain the gain in free energy by an increased classical hydrophobic effect due to the presence of additional nonpolar cyclohexyl residues throughout the polymer chain. For biological applications, it is desirable to keep the polymer size close to the size of the protein

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

Synthesis and binding studies of two new macrocyclic receptors for the stereoselective recognition of dipeptides

• Ana Maria Castilla,
• M. Morgan Conn and
• Pablo Ballester

Beilstein J. Org. Chem. 2010, 6, No. 5, doi:10.3762/bjoc.6.5

• showed neither enantio- nor diastereoselectivity in the recognition of the same substrates (Table 3). The difference in free energy measured for the complexes of 2 with the four diastereoisomers of Ala-Ala was in the order of 0.3 kcal/mol. We also investigated the complexation affinity of the cyclic

Mitomycins syntheses: a recent update

• Jean-Christophe Andrez

Beilstein J. Org. Chem. 2009, 5, No. 33, doi:10.3762/bjoc.5.33

The vicinal difluoro motif: The synthesis and conformation of erythro- and threo- diastereoisomers of 1,2-difluorodiphenylethanes, 2,3-difluorosuccinic acids and their derivatives

• David O'Hagan,
• Henry S. Rzepa,
• Martin Schüler and
• Alexandra M. Z. Slawin

Beilstein J. Org. Chem. 2006, 2, No. 19, doi:10.1186/1860-5397-2-19

• originating predominantly from entropy and zero-point energy corrections (1.06 kcal/mol). This is also the conformer that most closely represents the X-ray structure (Figure 1). The solvent correction (which takes into account free energy differences associated with the solvent cavity, but does not allow for

• free energy differences arising from vibrational terms) does not alter the relative energies of a and b, despite a having a zero dipole moment and b having a relatively large value (3.5D) [26]. Although the more polar b should perhaps gain more from electrostatic solvation, it has a smaller solvent