Conformational analysis and intramolecular interactions in monosubstituted phenylboranes and phenylboronic acids

• Josué M. Silla,
• Rodrigo A. Cormanich,
• Roberto Rittner and
• Matheus P. Freitas

Beilstein J. Org. Chem. 2013, 9, 1127–1134, doi:10.3762/bjoc.9.125

• due to hyperconjugation than 1c, which is sterically less hindered (see the lower Lewis-type energy in Table 1); the larger steric and electrostatic repulsion in 1b is due to the interacting oxygen lone pairs. In polar solvents, the electrostatic effect is minimized and the energy difference between

• ) because of the loss in hyperconjugative energy due to the lack of πCC→pB interaction, these geometries are at least located as local minima for 7–9. The important hyperconjugation nX→pB (especially for the NH2 derivative) obtained by NBO analysis (Table 5) indicates that N, S and P are considerably better

Conformational analysis, stereoelectronic interactions and NMR properties of 2-fluorobicyclo[2.2.1]heptan-7-ols

• Fátima M. P. de Rezende,
• Marilua A. Moreira,
• Rodrigo A. Cormanich and
• Matheus P. Freitas

Beilstein J. Org. Chem. 2012, 8, 1227–1232, doi:10.3762/bjoc.8.137

• hyperconjugation); this can be achieved by deleting all interactions involving antibonding and Rydberg orbitals in a molecule and then computing the energy of this hypothetical system. Accordingly, the global minimum was found to be the most destabilized form in terms of steric effects (possibly because of the nF

Dioxane dibromide mediated bromination of substituted coumarins under solvent-free conditions

• Subrata Kumar Chaudhuri,
• Sanchita Roy and
• Sanjay Bhar

Beilstein J. Org. Chem. 2012, 8, 323–329, doi:10.3762/bjoc.8.35

• electron-donating inductive effect and hyperconjugation as well as the mesomeric effect of the electron-donating substituent at C7. After concomitant loss of highly acidic hydrogen from C3, the carbocationic intermediate was re-aromatized leading to vinylic substitution (Table 1, entries 2–7). It is

Computational evidence for intramolecular hydrogen bonding and nonbonding X···O interactions in 2'-haloflavonols

• Tânia A. O. Fonseca,
• Matheus P. Freitas,
• Rodrigo A. Cormanich,
• Teodorico C. Ramalho,
• Cláudio F. Tormena and
• Roberto Rittner

Beilstein J. Org. Chem. 2012, 8, 112–117, doi:10.3762/bjoc.8.12

• flavonol (see Supporting Information File 1). NBO analysis at the B3LYP/aug-cc-pVDZ level gives the hyperconjugation contribution for this interaction (n(C=)O → σ*OH) as 6.9 kcal mol−1, while the QTAIM data confirms the establishment of intramolecular HB as a stable, electrostatic interaction (see below

β-Hydroxy carbocation intermediates in solvolyses of di- and tetra-hydronaphthalene substrates

• Jaya S. Kudavalli and
• Rory A. More O'Ferrall

Beilstein J. Org. Chem. 2010, 6, 1035–1042, doi:10.3762/bjoc.6.118

• formation of a β-hydroxynaphthalenium carbocation with a conformation in which a C–OH occupies an axial position β to the carbocation centre preventing stabilisation of the carbocation by C–H hyperconjugation, which would occur in the conformation initially formed from the cis isomer. It is suggested that C

• –H hyperconjugation is particularly pronounced for a β-hydroxynaphthalenium ion intermediate because the stability of its no-bond resonance structure reflects the presence of an aromatic naphthol structure. Keywords: aromaticity; β-hydroxycarbocations; hyperconjugation; solvolysis; Introduction Cis

• , namely that the arenium ion intermediates are strongly stabilised by hyperconjugation between the carbocationic charge centre and a β-C–H bond, and that this effect is amplified by the contribution of an aromatic structure to the no-bond resonance form (15b) of the valence bond representation of this

Redox-active tetrathiafulvalene and dithiolene compounds derived from allylic 1,4-diol rearrangement products of disubstituted 1,3-dithiole derivatives

• Filipe Vilela,
• Peter J. Skabara,
• Christopher R. Mason,
• Thomas D. J. Westgate,
• Asun Luquin,
• Simon J. Coles and
• Michael B. Hursthouse

Beilstein J. Org. Chem. 2010, 6, 1002–1014, doi:10.3762/bjoc.6.113

• through hyperconjugation and delocalisation of the positive charge, which could complicate the pinacol mechanism. Related reactions of allylic alcohols are not unknown: periodic acid has been shown to oxidise one of the alcohol groups in a 1,4-diol fragment to yield the corresponding aldehyde, without any

The C–F bond as a conformational tool in organic and biological chemistry

• Luke Hunter

Beilstein J. Org. Chem. 2010, 6, No. 38, doi:10.3762/bjoc.6.38

• conformational tool for the synthesis of shape-controlled functional molecules. This review will begin by describing some general aspects of the C–F bond and the various conformational effects associated with C–F bonds (i.e. dipole–dipole interactions, charge–dipole interactions and hyperconjugation). Examples

• in these systems. Hyperconjugation effects Consider the well-studied molecule 1,2-difluoroethane (11, Figure 1c). There are two possible staggered conformers, with the fluorine atoms either gauche or anti. NMR and molecular modelling studies have shown that the gauche conformer is lower in energy

• conformer of 11, both σ*CF orbitals are aligned with adjacent C–H bonds, which can donate electron density into the σ*CF orbitals in a process known as hyperconjugation [1][2]. Feeding electron density into an antibonding orbital in this way is equivalent to partially breaking the bond, so when