Angular Group Induced Bond Alternation Research Articles

Molecular Structure of Salicylic Acid and Its Hydrates: A Rotational Spectroscopy Study.

We present a study of salicylic acid and its hydrates, with up to four water molecules, done by employing chirped-pulse Fourier transform microwave spectroscopy. We employed the spectral data set of the parent, 13C, and 2H isotopologues to determine the molecular structure and characterize the intra- and intermolecular interactions of salicylic acid and its monohydrate. Complementary theoretical calculations were done to support the analysis of the experimental results. For the monomer, we analyzed structural properties, such as the angular-group-induced bond alternation (AGIBA) effect. In the microsolvates, we analyzed their main structural features dominated by the interaction of water with the carboxylic acid group. This work contributes to seeding information on how water molecules accumulate around this group. Moreover, we discussed the role of cooperative effects further stabilizing the observed inter- and intramolecular hydrogen bond interactions.

Natural bond orbital (NBO) analysis of the angular group induced bond alternation (AGIBA) substituent effect

AbstractThe geometries, natural charges, and resonance structures of 11 monosubstituted benzene derivatives were analyzed at the B3LYP/6‐311++G(d,p) and HF/6‐311++G(d, p) levels of theory. The following angular substituents were chosen: OCH3, CH2CH3, OH, SH, NHCH3, NHNH2, NO, CHCH2, NCH2, NNH, and CHO. The analysis of resonance structures was performed by using two different methodologies: harmonic oscillator stabilization energies (HOSE) and natural resonance theory (NRT). Also, the natural bond orbital (NBO) donor–acceptor stabilization energies for different resonance structures were calculated. We found that for all the substituents, the purely geometric resonance stabilization parameter (HOSE) is linearly correlated with quantum chemically derived resonance structure weight (NRT) of a given structure. Also, the calculations provide qualitative support for the earlier assumption of a through space angular group induced bond alternation (AGIBA) effect. Copyright © 2010 John Wiley & Sons, Ltd.

Angular Group Induced Bond Alternation (AGIBA). A New Face of Substituent Effect Detected in Molecular Geometry.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Angular Group Induced Bond Alternation (AGIBA). A New Face of Substituent Effect Detected in Molecular Geometry

Angular Group Induced Bond Alternation (AGIBA). A New Face of Substituent Effect Detected in Molecular Geometry

Angular Group Induced BondAlternation (AGIBA). A New Face of Substituent Effect Detectedin Molecular Geometry

Angular Group Induced Bond Alternation is a new face of a substituent effect well documented by careful analysis of molecular geometry. The angular groups attached to monocyclic 6-π-electron systems cause substantial changes to π-electron distribution in the ring. Different patterns are found for X-Y and X=Y types of groups. The overall effect is due to the rehybridization effect, the through space π-electron interactions between a group and the ring, possibly also by other subtle effects, eg. the negative hyperconjugation. The effect is strongly conformational dependent. While the AGIBA is energetically weak, it is structurally strong enough that other interactions in monocyclic systems, eg. through - resonance type interactions do not reduce it. In polycyclic benzenoid hydrocarbons AGIBA works only locally while in non-cyclic π-electron systems the effect does not work at all.

Bond angles and bond lengths in monosubstituted benzene and ethene derivatives: a comparison of computational and crystallographic results.

Bond angles and bond lengths in 29 monosubstituted benzene derivatives and in the same number of ethene derivatives were calculated at the B3LYP/6-311+G(d,p) level. Angle deformations in benzene derivatives agree reasonably with those derived statistically from the crystallographic data; in the case of small deformations, the calculated parameters are even more reliable. There is little correlation between geometry and reactivity parameters (sigma-constants) in spite of some previous claims. Nevertheless, three components of the substitution effect can be distinguished: (a) strong deformation of the adjoining angles and bonds can be ascribed to changes of hybridization; (b) a weaker effect in the meta and para positions is only partially related to resonance; (c) in the case of unsymmetrical substituents, the symmetry of the benzene ring is also broken - the angular group-induced bond alternation (AGIBA) effect. The latter effect was also confirmed by searches in the Cambridge Structural Database for alkoxy, alkylthio, acyl and azo derivatives.

Angular group induced bond alternation (AGIBA) observed in aromatic azine derivatives

Angular group induced bond alternation (AGIBA) observed in aromatic azine derivatives

Angular group induced bond alternation (AGIBA). Part VI — Competition between the AGIBA and through resonance effects

Angular group induced bond alternation (AGIBA). Part VI — Competition between the AGIBA and through resonance effects

Angular group induced bond alternation (AGIBA). Part VI — Competition between the AGIBA and through resonance effects

AbstractAnalysis of the molecular geometry of three experimental model compounds, 2,3‐dimethyl‐p‐anisaldehyde, 2,5‐dimethyl‐p‐anisaldoxime and 2,3‐dimethyl‐p‐anisaldoxime, and eight compounds (p‐nitrosoaniline, p‐nitroanisole and two conformers each of p‐nitrosoanisole, p‐anisaldehyde and p‐anisaldimide) whose molecular geometry was obtained by optimization at the B3LYP/6–311G** level of theory, where both the AGIBA and through resonance effects were present, led to the conclusion that the competition between these effects does not reduce any of them significantly. Copyright © 2001 John Wiley & Sons, Ltd.

Angular group‐induced bond alternation (AGIBA). Part 5—Conformation dependence and additivity of the effect: structural studies of 3,5‐dimethoxybenzaldehyde ­derivatives and related systems

AbstractX‐ray structure analysis of 3,4,5‐trimethoxybenzadehyde and 3,5‐dimethoxy‐4‐(1‐bromoethoxy)benzaldehyde gave their molecular geometries which showed a vague AGIBA effect. To clarify the situation, ab initio optimizations at the MP2/6–31G** level of theory of 12 conformers of 1,3,5‐trimethoxy‐, 1,3‐dimethoxy‐5‐formyl‐, 1,3‐diformyl‐5‐methoxy‐ and 1,3,5‐triformylbenzene derivatives were carried out. The results support the occurrence of additive AGIBA effects, even if some weak interactions are possible between the methoxy and formyl groups. Copyright © 2001 John Wiley & Sons, Ltd.

Angular Group Induced Bond Alternation (AGIBA). Part 4: Does the Effect Operate in the Systems with Alternated Bonds?

Angular groups attached to non-cyclic π-electron systems like amidine or 1,3-butadiene do not exhibit the AGIBA effect, whereas when attached to aromatic systems they act in an ambiguous way—the effect is much more local than in the cases observed in monocyclic systems (benzene, s-triazine). The above picture is based upon ab initio calculations at B3LYP/6-311+G ∗∗ level of theory for 2,3,6,7- and 1,4,5,8-tetramethoxynaphthalene, 9,10-dimethoxyphenanthrene, 4,9- and 4,10-dinitrosopyrene derivatives of C 2 or i symmetry, and X-substituted 1,3-butadiene (X=NO, CHO, NNH, CHCH 2 and OCH 3) at B3LYP/6-31G ∗ for C- substituted derivatives of formamidine substituted derivatives of formamidine (X=NO, CHO, NNH, CHCH2, OCH 3 and CH 2CH 3).

Angular group-induced bond alternation. III. The case of ortho-dimethoxybenzene derivatives. Crystal and molecular structure of 3,4-dimethoxybenzaldehyde (4-methylphenyl)sulfonylhydrazone

The crystal and molecular structure of the 3,4-dimethoxybenzaldehyde (4-methylphenyl)-sulfonylhydrazone is reported, with R = 0.0647. Application of the HOSE model to the molecular geometry of the title compound, together with the most precise molecular geometries for 36 ortho-dimethoxy derivatives of benzene retrieved from Cambridge Structural Database (CSD) and supplemented by ab initio RHF/6-311G ∗∗ calculations, led to the conclusion that the o-dimethoxy groups cause significant changes in ring geometry, fully in line with the concept of Angular Group Induced Bond Alternation (AGIBA).

Angular group-induced bond alternation II. The magnitude and the nature of the effect and its application to polynuclear benzenoid systems

By careful selection of ‘angular’ substituents it is possible to induce sizeable deformations of benzene ring structures, which correspond to bond length alternation. Ab initio calculations are used to explore the range of this effect in 1,3,5-trisubstituted benzenes with 14 different substituents (-CH 2NH 2, -OCH 3, -CH 2CH 3, -SCH3, -NHNH 2, -NHCH 3, -OH, -SH, -NCH 2, -CHCH 2, -COH, -NO, -NNH, -CHNH). The effect is strongly conformation-dependent, and for C 3-symmetrical compounds is additive, in the sense that the induced π-localization is three times larger than in the analogous mono-substituted benzenes. This reflects a new approach to understanding how substituent effects operate in organic chemistry, which is not directly related to ‘electron-withdrawing’ or ‘electron-donating’ power, but rather on the substituent conformation (and on whether it contains single or double bonds). The effect is explored in polynuclear benzenoid systems (the trimethoxyphenalene cation, and tetramethoxyperylene). The nature of the effect is examined by analyzing the ring and substituent energies. Finally, the probable chemical consequences of such substitution pattern are discussed.

Angular-group-induced bond alternation. I. Origin of the effect from Ab Initio calculations

It is shown that an angular group -XY attached to the benzene ring causes bond length alternation within the ring. This angular-group-induced bond alternation (AGIBA) effect is studied in several mono-substituted benzene derivatives by means of the ab initio calculations. Different alternation patterns are found for angular groups of the -X-Y and -X=Y types. The origin of the AGIBA effect is traced to a competing influence of through-space-π-electron interactions and a rehybridization effect at the substituted carbon atom. The AGIBA effect is shown to be strongly conformation dependent.