Implications of hyperconjugative effects on bond lengths of allylic systems. An NBO investigation

Bocca, Cleverson C.; Pontes, Rodrigo M.; Basso, Ernani A.

doi:10.1016/j.theochem.2004.08.033

Cited by 9 publications

(5 citation statements)

References 21 publications

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“…Part of the challenge is that structural effects of neutral hyperconjugation are often small and indirect experimental approaches can thus be complicated 104. For example, Basso and coworkers105 reported that although calculated structural parameters (bond lengths, valence and dihedral angles) and NBO analysis were in a good agreement with the expected trends of hyperconjugative interactions between a double bond and an allylic substituent (for M = C, Si, Ge), neither computed nor experimental NMR CC coupling constants,1J CC , in these systems correlated with the structural parameters.…”

Section: Types Of Hyperconjugationmentioning

confidence: 99%

Hyperconjugation

Alabugin

Gilmore

Peterson

2011

WIREs Comput Mol Sci

288

289

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This review outlines the ubiquitous nature of hyperconjugative interactions and their role in the structure and reactivity of organic molecules. After defining the common hyperconjugative patterns, we discuss the main factors controlling the magnitude of hyperconjugative effects, including orbital symmetry, energy gap, electronegativity, and polarizibility. The danger of underestimating the magnitude of hyperconjugative interactions are illustrated by a number of spectroscopic, conformational, and structural effects. Through the use of advanced computational techniques, the true role of hyperconjugative effects, as it pertains to their influence on stereoelectronics, conformational equilibria, and reactivities relative to other electronic effects, continue to be uncovered.

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Section: Types Of Hyperconjugationmentioning

confidence: 99%

Hyperconjugation

Alabugin

Gilmore

Peterson

2011

WIREs Comput Mol Sci

288

289

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“…Such a -bond/-system interaction, named as hyperconjugation (Mullins, 2012) can readily be explained by analogy with the -donor behavior of a lone pair-bearing atom (e.g., chlorine) to an empty p orbital, though C---C or C---H bonds (rather than electron lone pairs) of the alkyl group are involved as electron-releasing units in hyperconjugative interactions. Interestingly, → * interactions (negative hyperconjugation) are usually negligible for alkyl groups lacking electronegative atoms (Bocca, Pontes, & Basso, 2004).…”

Section: Introductionmentioning

confidence: 99%

The alkyl group is a -I + R substituent

Salvatella

2018

Educación Química

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Electronic substituent effects are usually classified as inductive (through σ-bonds) and resonance effects (via π-bonds). The alkyl group has been usually regarded as aσ -electron donor substituent (+I effect, according to the Ingold’s classification). However, a σ-withdrawing, π-donor effect (-I + R pattern) allows explaining the actual electron-withdrawing behavior of alkyl groups when bound to sp³ carbon atoms as well as their well-known electron-releasing properties when attached to sp² or sp atoms. Alkyl substitution effects on several molecular properties (dipole moments, NMR, IR, and UV spectra, reactivity in gas phase and solution) are discussed.

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“…Theoretical ab initio and DFT calculations of a variety of ylides − and related species − have been reported to explain their structure, bonding, or internal rotational processes. In a number of cases, the importance of the π→σ* or n→σ* anomeric effects, now more generally termed negative hyperconjugation , , in understanding conformational preferences has been pointed out. − The natural bond orbital (NBO) approach of Weinhold et al has been frequently used to quantify the substituent dependence of hyperconjugation , as well as negative hyperconjugation − within the context of conformational analysis. Reports on the theoretical investigations on how the hyperconjugative and related interactions influence the structural parameters in the pyridinium ylides are, however, still scarce, and the main goal of this work is to highlight the influence of such interactions on the conformational preferences of these synthetically important intermediates.…”

Section: Introductionmentioning

confidence: 99%

Substituent-Dependent Anomeric Effects as a Source of Conformational Preference in Pyridinium Methylides

2006

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A systematic density functional theory level investigation of differently substituted pyridinium methylides was carried out to determine the role of C(ylidic) lone-pair-associated hyperconjugative and negative hyperconjugative interactions in deciding conformational preferences. Deviation from the coplanar orientation of the carbanionic center with the pyridine ring and its substituent dependence has been found to correlate well with the relative opportunities for conjugative and negative hyperconjugative interactions of a ylidic moiety with different substituent groups present at the ylidic carbon. The contribution of individual n-->pi* conjugative, n-->sigma* negative hyperconjugative, and sigma-->pi* hyperconjugative interactions in a particular conformation of pyridinium dichlorophosphinomethylides was assessed from donor-acceptor stabilization energies, as obtained from natural bond orbital (NBO) analysis. The relative extent of conjugative and negative hyperconjugative interactions with the substituents present at the ylidic carbon plays an important role in permitting the delocalization of ylidic charge into the pyridine ring, thereby controlling the relative orientation of the latter with the carbanionic plane.

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Implications of hyperconjugative effects on bond lengths of allylic systems. An NBO investigation

Cited by 9 publications

References 21 publications

Hyperconjugation

Hyperconjugation

The alkyl group is a -I + R substituent

Substituent-Dependent Anomeric Effects as a Source of Conformational Preference in Pyridinium Methylides

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