A comparative molecular field analysis of the structure of cycloimmonium ylides. A derived synthesis methodology for planar and non-planar cycloimmonium ylides

Karzazi, Y.; Vergoten, Gérard; Surpateanu, Gheorghe

doi:10.1016/s0022-2860(98)00529-8

Cited by 4 publications

(2 citation statements)

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“…on the ylidic carbon, − however, revealed that the relative orientation of the plane of the pyridine ring and the carbanionic center varies to a great extent from nearly coplanar to almost perpendicular and requires an explanation. Recently, several theoretical studies 3,9-12 of the pyridinium methylides have appeared in the literature where the results have been found to be in good agreement with the experimental geometries, and in a few cases, , the spatial arrangement of two moieties has also been addressed. In α-keto stabilized ylides, the observed noncoplanarity has been assigned to the presence of a 1,4-N···O interaction, whereas the stabilization of a coplanar conformation in other cases has been attributed to the presence of 1,6-C−H···O hydrogen bonding .…”

Section: Introductionmentioning

confidence: 77%

“…In α-keto stabilized ylides, the observed noncoplanarity has been assigned to the presence of a 1,4-N···O interaction, whereas the stabilization of a coplanar conformation in other cases has been attributed to the presence of 1,6-C−H···O hydrogen bonding . In a comparative molecular field analysis study of differently substituted pyridinium methylides, the deviation from coplanarity has been correlated to the cumbersomeness of the substituent present on the ylidic carbon …”

Section: Introductionmentioning

confidence: 99%

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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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