Experimental charge maps in di-activated carbanions: access to charge demands of primary electron-withdrawing functionalities

Barchiesi, Emma; Bradamante, Silvia; Ferraccioli, Raffaella; Pagani, Giorgio A.

doi:10.1039/p29900000375

Cited by 23 publications

(20 citation statements)

References 33 publications

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“…These signals appear at slightly lower field with respect to the protons of benzene (Dd ~0.5) and therefore, as expected, the electron-withdrawing power of the carbonyl group deshields the protons directly attached to the phenyl ring. The 13 C{ 1 H}-NMR spectrum shows the same pattern reported for Na(dpp) 22 with the carbonyl carbon that displays sizeable high-field shift relative to the analogous carbon of the neutral Hdpp (Dd = 2), 22,23 while a low-field shift is observed for the ipso carbon of the phenyl ring due to the deshielding contribution of the electron-withdrawing of the carbonyl group.…”

Section: Syntheses and Spectral Datasupporting

confidence: 63%

“…The 1 H-NMR spectrum for [{Ca(dpp) 2 } n ] exhibits a sharp singlet at d H = 6.64 due to the methine (C-H) proton that does not shift appreciably from resonances of the methine proton in the Hdpp sodium salts (lit., 22 d H = 6.30), and three sets of signals in the aromatic region assigned to the phenyl hydrogen resonance. These signals appear at slightly lower field with respect to the protons of benzene (Dd ~0.5) and therefore, as expected, the electron-withdrawing power of the carbonyl group deshields the protons directly attached to the phenyl ring.…”

Section: Syntheses and Spectral Datamentioning

confidence: 99%

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Synthesis and characterization of calcium β-diketonate complexes. X-Ray crystal and molecular structures of: [{Ca(tmhd)2}2(18-crown-6)], [Ca(dpp)2(thf)2] and [Ca(dpp)2(triglyme)]

Habra¹,

Benetollo²,

Casarin³

et al. 2010

Dalton Trans.

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Reactions of 2,2,6,6-tetramethyl-3,5-heptanedione (Htmhd), 1,1,1,5,5,5-hexafluoro-2,4-pentanedione (Hhfa) or 1,3-diphenyl-1,3-propanedione (Hdpp) with calcium methoxide in hexane or toluene afford the corresponding known oligomeric beta-diketonates: [Ca(3)(tmhd)(6)], [{Ca(hfa)(2)}(n)] and [{Ca(dpp)(2)}(n)]. The complexes react with tetrahydrofuran, 2,5,8,11-tetraoxadodecane (triglyme) or 1,4,7,10,13,16-hexaoxacyclooctadecane (18-crown-6) leading to the formation of the new mononuclear [Ca(dpp)(2)(thf)(2)], [Ca(dpp)(2)(triglyme)] and dinuclear [{Ca(dpp)(2)}(2)(18-crown-6)] and [{Ca(tmhd)(2)}(2)(18-crown-6)] adducts. The obtained complexes were characterized by elemental analyses, IR, (1)H and (13)C NMR spectroscopies; moreover, single crystal X-ray diffraction measurements were also carried out for: [{Ca(tmhd)(2)}(2)(18-crown-6)], [Ca(dpp)(2)(thf)(2)] and [Ca(dpp)(2)(triglyme)].

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Section: Syntheses and Spectral Datasupporting

confidence: 63%

Section: Syntheses and Spectral Datamentioning

confidence: 99%

Synthesis and characterization of calcium β-diketonate complexes. X-Ray crystal and molecular structures of: [{Ca(tmhd)2}2(18-crown-6)], [Ca(dpp)2(thf)2] and [Ca(dpp)2(triglyme)]

Habra¹,

Benetollo²,

Casarin³

et al. 2010

Dalton Trans.

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“…These relationships have been validated by means of their successful application to a large number of anions of benzyl and methylene derivatives of primary organic functionalities, , pyridines, 7a, azines, and azoles . In particular, the π-charge/ 13 C-shift relationship (1) makes possible the empirical calculation of the π-electron density q π C on a trigonal carbanionic carbon XYZC - ; 15a, relationship 2 (derived from relationship 1) allows the calculation of the variation in π-electron density for every carbon site on going from the neutral to the conjugate anionic system; and finally the π-charge/ 15 N-shift relationship (3) 6,7,8,16 can be used to compute the same local variation for a nitrogen atom …”

Section: Resultsmentioning

confidence: 99%

A NMR Investigation of α-Heterosubstituted Chloroethyllithiums in THF

Abbotto¹,

Bradamante²,

Florio³

et al. 1997

J. Org. Chem.

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“…Over the last 10 years, we have proposed 13 C (relationships 1 and 2) , and 15 N (relationship 3) − shift/π-charge relationships as a method of choice for experimentally mapping π-charges and ranking the resonance electron-withdrawing power of primary organic functionalities ,, and heterocycles, including azines (2- and 4-pyridyl, pyrazinyl, 4-pyrimidyl, 3-pyridazinyl, and 2- and 4-quinolyl), ,, 1,3-azoles (2-oxazolyl, 2-thiazolyl, 2-imidazolyl, and their benzo-fused analogues), and purines (8-purinyl) …”

mentioning

confidence: 99%

Diheteroarylmethanes. 8.¹ Mapping Charge and Electron-Withdrawing Power of the 1,2,4-Triazol-5-yl Substituent

Abbotto¹,

Bradamante²,

Facchetti³

et al. 1999

J. Org. Chem.

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Three new triazolyl derivatives, bis(1H-1-phenyl-1,2,4-triazol-5-yl)methane (11), 1H-1-phenyl-5-(beta-styryl)-1,2,4-triazole (12), and 1H-5-benzyl-1-phenyl-1,2,4-triazole (13) have been synthesized and the carbanions 11(-)() and 13(-)() investigated in DMSO by multinuclear NMR spectroscopy. By applying previously proposed and widely used pi-charge/(13)C shift relationships on the spectra of the anions, it is possible to rank the pi electron-withdrawing power of the 1,2,4-triazol-5-yl group in terms of charge demand c(X), a quantity that represents the fraction of pi negative charge delocalized by the heterocyclic ring. Our results indicate that the charge demand c(X) of this heterocycle is considerably greater than that of other 1,3-azoles (2-imidazolyl, 2-oxazolyl, 2-benzoimidazolyl), being close to that of some mono- and diazinyl substituents. A single set of resonances is presented by both carbanions 11(-)() and 13(-)(), thus showing that they exist either as a single geometric isomer species or as a mixture of isomers in a rapid (on the NMR time scale) equilibrium. (13)C and (15)N shift/pi-charge relationships allow accurate pi-charge mapping of carbanionic systems. Our results clearly show that, in the case of benzyl carbanion 13(-)(), all of the three nitrogen atoms are almost equally involved in delocalizing the negative charge. Also, the N-phenyl group contributes to charge delocalization. Anion 11(-)()( )()is the first of the bis(heteroaryl)methyl carbanions that we have studied, in which all of the negative charge originated by deprotonation of the carbon acid 11 is hosted on the nitrogen atoms without any appreciable involvement of the heteroaromatic carbon frame.

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Experimental charge maps in di-activated carbanions: access to charge demands of primary electron-withdrawing functionalities

Cited by 23 publications

References 33 publications

Synthesis and characterization of calcium β-diketonate complexes. X-Ray crystal and molecular structures of: [{Ca(tmhd)2}2(18-crown-6)], [Ca(dpp)2(thf)2] and [Ca(dpp)2(triglyme)]

Synthesis and characterization of calcium β-diketonate complexes. X-Ray crystal and molecular structures of: [{Ca(tmhd)2}2(18-crown-6)], [Ca(dpp)2(thf)2] and [Ca(dpp)2(triglyme)]

A NMR Investigation of α-Heterosubstituted Chloroethyllithiums in THF

Diheteroarylmethanes. 8.¹ Mapping Charge and Electron-Withdrawing Power of the 1,2,4-Triazol-5-yl Substituent

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Experimental charge maps in di-activated carbanions: access to charge demands of primary electron-withdrawing functionalities

Cited by 23 publications

References 33 publications

Synthesis and characterization of calcium β-diketonate complexes. X-Ray crystal and molecular structures of: [{Ca(tmhd)2}2(18-crown-6)], [Ca(dpp)2(thf)2] and [Ca(dpp)2(triglyme)]

Synthesis and characterization of calcium β-diketonate complexes. X-Ray crystal and molecular structures of: [{Ca(tmhd)2}2(18-crown-6)], [Ca(dpp)2(thf)2] and [Ca(dpp)2(triglyme)]

A NMR Investigation of α-Heterosubstituted Chloroethyllithiums in THF

Diheteroarylmethanes. 8.1 Mapping Charge and Electron-Withdrawing Power of the 1,2,4-Triazol-5-yl Substituent

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Diheteroarylmethanes. 8.¹ Mapping Charge and Electron-Withdrawing Power of the 1,2,4-Triazol-5-yl Substituent