Exocyclic push–pull conjugated compounds. Part 3. An experimental NMR and theoretical MO ab initio study of the structure, the electronic properties and barriers to rotation about the exocyclic partial double bond in 2-exo-methylene- and 2-cyanoimino-quinazolines and -benzodiazepines

Benassi, Rois; Bertarini, Claudio; Hilfert, Liane; Kempter, G.; Kleinpeter, Erich; Spindler, J.; Taddei, F.; Thomas, Steffen

doi:10.1016/s0022-2860(99)00346-4

Cited by 25 publications

(12 citation statements)

References 25 publications

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“…For 2, interconversion via rotation appears to be slightly preferred over N-inversion, and thus in contrast to most literature reports, although exceptions based on calculations do exist. 16 This apparently anomalous result, however, would be consistent with a lowering of the N-C 2 0 bond order. Furthermore, it is noted that although the transition-state energy for the rotation of 2 is similar to that of 1, the transition-state energy for N-inversion is much greater in comparison with 1 and is essentially invariant to the transition-state energy for rotation.…”

Section: Determination Of Interconversion Mechanismmentioning

confidence: 94%

“…For variabletemperature measurements down to 95°C, NMR spectra were acquired at 11.75 T on an NMR spectrometer equipped with a 5 mm normal configuration tunable probe operating at 500. 16 …”

Section: Experimental Nmr Measurementsmentioning

confidence: 99%

“…16 In particular, N-inversion has been decisively declared to be the sole mechanism in effect for the iminocarbonates 4b,5b,5c, 6 and iminodithiocarbonates.…”

Section: Introductionmentioning

confidence: 99%

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Configuration andE/Zinterconversion mechanism ofO(S)-allyl-S(O)-methyl-N-(acridin-9-yl) iminothiocarbonate

et al. 2005

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The configuration and dynamic behavior of O-allyl-S-methyl-N-(acridin-9-yl)iminothiocarbonate (1) and its S-allyl-O-methyl regioisomer (2) were studied using quantum chemical calculations and by applying a novel graphical method to scatter maps obtained from MD simulations for evaluation of an NOE-weighted internuclear distance (r(NOE)). Energy calculations indicated that the Z configuration was predominant for each compound and, further, this was supported both by the calculated chemical shifts and the r(NOE). Both N-inversion- and rotation-type transition-state structures were also calculated for the E/Z isomerization process, the results indicating that the preferred interconversion mechanism for 1 is N-inversion, but contrastingly, interconversion via rotation is equally as probable as N-inversion for 2. This supports the notion that one or the other or both pathways can be active and each system needs to be assessed on a case-by-case basis.

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Section: Determination Of Interconversion Mechanismmentioning

confidence: 94%

Section: Experimental Nmr Measurementsmentioning

confidence: 99%

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Configuration andE/Zinterconversion mechanism ofO(S)-allyl-S(O)-methyl-N-(acridin-9-yl) iminothiocarbonate

et al. 2005

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“…In the 13 C-NMR spectra ((D 6 )DMSO or CDCl 3 ), the C-atoms of the exocyclic formal C,C-double bond absorb at 148-146 ppm (C(2)) and 26-23 ppm (=C(CN) 2 ), which is characteristic of this type of 'push-pull' system [17] [18]. These chemical shifts indicate a highly zwitterionic character of these compounds in solution, resulting in a low rotational barrier about the exocyclic C=(CN) 2 bond [17]. In accordance with this interpretation is the fact that only one CN signal appears in the 13 C-NMR spectrum.…”

Section: Methodsmentioning

confidence: 99%

Reactions of 2-Unsubstituted 1H-Imidazole 3-Oxides with 2,2-Bis(trifluoromethyl)ethene-1,1-dicarbonitrile: A Stepwise 1,3-Dipolar Cycloaddition

Mlostoń

Jasiński

Linden

et al. 2006

HCA

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The reaction of 1,4,5-trisubstituted 1H-imidazole-3-oxides 1 with 2,2-bis(trifluoromethyl)ethene-1,1-dicarbonitrile (7, BTF) yielded the corresponding 1,3-dihydro-2H-imidazol-2-ones 10 and 2-(1,3-dihydro-2H-imidazol-2-ylidene)malononitriles 11, respectively, depending on the solvent used. In one example, a 1 : 1 complex, 12, of the 1H-imidazole 3-oxide and hexafluoroacetone hydrate was isolated as a second product. The formation of the products is explained by a stepwise 1,3-dipolar cycloaddition and subsequent fragmentation. The structures of 11d and 12 were established by X-ray crystallography.

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“…This value lies in the range of cumulative charges experimentally derived for the COO À group of typically zwitterionic systems, such as the amino acids l-alanine [31] and a-glycine [24] [À0.59(2) e and À0.97(3) e, respectively]. Interestingly, the imidazolidine ring is virtually neutral, having a net charge of À0.04(13) e, while the positive contribution to satisfy the electroneutrality of the system is entirely due to the isopropyl groups, contributing + 0.54 (14) e and + 0.32 (15) e to the total molecular charge. For a comparison with the experimental X-ray atomic charges, RHF/6±31 G** and B3 LYP/6±31 G** theoretical calculations on the isolated PPE molecule were also performed.…”

Section: Electrostatic Propertiesmentioning

confidence: 99%

Electron Density Investigation of a Push–Pull Ethylene (C₁₄H₂₄N₂O₂⋅H₂O) by X‐ray Diffraction atT= 21 K

Forni¹,

Destro²

2003

Chemistry A European J

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The electron charge distribution in a strongly twisted push-pull ethylene [PPE, 3-(1,3-diisopropyl-2-imidazolidinylidene)-2,4-pentanedione] has been determined by low temperature (T = 21 K) single-crystal X-ray diffraction analysis. The derived electronic properties are consistent with a zwitterionic molecule, as indicated by a charge transfer of 0.82(16) e from the push to the pull moieties and a charge polarization of 0.29(7) e on the olefinic bond. A dipole moment of 12(3) D has been determined, which compares well with ab initio theoretical results in terms of both modulus and orientation. The second moments, which have also been obtained with good precision, characterize PPE as a highly quadrupolar molecule. The special electronic features of the molecule confer particular topological properties to the electron density distribution, as evidenced by comparison with "standard" organic molecules. The crystallographic asymmetric unit of the present system includes one water molecule, which is hydrogen bonded to PPE. Its topological properties have also been investigated, together with an analysis of the hydrogen bonds involved.

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Exocyclic push–pull conjugated compounds. Part 3. An experimental NMR and theoretical MO ab initio study of the structure, the electronic properties and barriers to rotation about the exocyclic partial double bond in 2-exo-methylene- and 2-cyanoimino-quinazolines and -benzodiazepines

Cited by 25 publications

References 25 publications

Configuration andE/Zinterconversion mechanism ofO(S)-allyl-S(O)-methyl-N-(acridin-9-yl) iminothiocarbonate

Configuration andE/Zinterconversion mechanism ofO(S)-allyl-S(O)-methyl-N-(acridin-9-yl) iminothiocarbonate

Reactions of 2-Unsubstituted 1H-Imidazole 3-Oxides with 2,2-Bis(trifluoromethyl)ethene-1,1-dicarbonitrile: A Stepwise 1,3-Dipolar Cycloaddition

Electron Density Investigation of a Push–Pull Ethylene (C₁₄H₂₄N₂O₂⋅H₂O) by X‐ray Diffraction atT= 21 K

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Exocyclic push–pull conjugated compounds. Part 3. An experimental NMR and theoretical MO ab initio study of the structure, the electronic properties and barriers to rotation about the exocyclic partial double bond in 2-exo-methylene- and 2-cyanoimino-quinazolines and -benzodiazepines

Cited by 25 publications

References 25 publications

Configuration andE/Zinterconversion mechanism ofO(S)-allyl-S(O)-methyl-N-(acridin-9-yl) iminothiocarbonate

Configuration andE/Zinterconversion mechanism ofO(S)-allyl-S(O)-methyl-N-(acridin-9-yl) iminothiocarbonate

Reactions of 2-Unsubstituted 1H-Imidazole 3-Oxides with 2,2-Bis(trifluoromethyl)ethene-1,1-dicarbonitrile: A Stepwise 1,3-Dipolar Cycloaddition

Electron Density Investigation of a Push–Pull Ethylene (C14H24N2O2⋅H2O) by X‐ray Diffraction atT= 21 K

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Electron Density Investigation of a Push–Pull Ethylene (C₁₄H₂₄N₂O₂⋅H₂O) by X‐ray Diffraction atT= 21 K