Crystallographic studies of intra- and intermolecular interactions Part VII. Crystal and molecular structure of the complex of acridine—pentachlorophenol: H-bonding effect on the geometry of the pentachlorophenol moiety

Woźniak, Krzysztof; Krygowski, T.M.; Kariuki, Benson M.; Jones, William

doi:10.1016/0022-2860(91)80040-b

Cited by 17 publications

(16 citation statements)

References 13 publications

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“…This rule states that the valence angle at an atom X in a π-electron system increases when the electronegativity of a substituent R attached to X is increased. For example, in the case of acid−base complexes ROH···B ↔ RO - ···HB + between pentachlorophenol and various bases, it has been observed that the valence angle at the i -carbon of R increases when the hydrogen-bond proton is shifted from the base toward the oxygen atom …”

Section: Discussionmentioning

confidence: 99%

Combined X-ray Diffraction and ¹⁵N CPMAS NMR Study of Molecular Structure and Proton Order/Disorder Phenomena in Cyclic N,N‘-Bisarylformamidine Dimers

et al. 1997

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Crystal structures of a series of five symmetrically substituted N,N-bisarylformamidines ArNHsCHdNAr with Ar ) X-C 6 H 4 , X ) p-OCH 3 (IV), p-CH 3 (V), p-F (VI), p-NO 2 (VII), and m-Br (VIII) have been determined by single-crystal X-ray diffraction (XRD) and complete the series studied previously where X ) H (I), p-Br (II), and p-Cl (III). In addition, the results of variable-temperature 15 N CPMAS NMR experiments performed on 15 Nlabeled I, II, and IV are reported. All compounds form cyclic dimers linked by two NsH‚‚‚N hydrogen bonds which can form two different tautomers, a and b, interconverting by fast double proton transfers. The NMR experiments indicate three types of amidines characterized by different magnitudes of the equilibrium constants K ab of the tautomerism. In dimers of type such as V-VIII, we find K ab , 1 (i.e., only a single tautomer in the temperature range between 100 and 300 K). In this case, the hydrogen-bonded protons are ordered and can be localized by XRD. Furthermore, the C‚‚‚N bond lengths and torsional and valence angles involving the two aryl groups of an amidine unit are different. For dimers such as II and III, characteristic temperature dependent 15 N CPMAS NMR line shape changes are observed indicating that K ab ) 1 within the margin of error. Rate constants of the tautomerism can in this case be obtained by line shape analysis. For this degeneracy to occur, the aryl group conformations at both amidine nitrogen atoms must be similar. XRD then observes disordered hydrogen-bond protons and, in principle, also disordered nitrogen atoms. However, in practice, the disorder of the latter is not resolved leading to the observation of equalized C‚‚‚N bond lengths. Finally, dimers (I, IV) represent an intermediate case with K ab < 1, which could be labeled as "dynamic partial order". The implications of the molecular structure and the hydrogen bond and proton transfer characteristics are discussed.

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Section: Discussionmentioning

confidence: 99%

Combined X-ray Diffraction and ¹⁵N CPMAS NMR Study of Molecular Structure and Proton Order/Disorder Phenomena in Cyclic N,N‘-Bisarylformamidine Dimers

et al. 1997

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“…An approximate answer was given by a systematic study of pentachlorophenol H-bond complexes with various bases. It was shown that a -bond lengths, α angle, and CO bond lengths (for labeling, see Chart ) are nicely correlated with each other and with the correlation coefficient (or its absolute value, because it depends upon the sign of the slope) at the level of 0.94 or better 20 …”

Section: 2 Intermolecular H-bond Systems and Modeling Of The σ- And π...mentioning

confidence: 99%

“…Thus, the differentiation may be done by analysis of the magnitude of the slope of R (CO) versus a (av) dependences. The procedure for estimating the values of the slopes for these two cases is based on a model in which the limiting cases for CO and a (av) bonds are approximated by situations in which mostly the σ- or π-electronic mechanisms operate . Apart from the intermolecular case used for testing the model, it was also shown that, in the intramolecular H-bond system, N -salicylideneanilines, the dominant changes in geometry in the ring are due to the mesomeric effects …”

Section: 2 Intermolecular H-bond Systems and Modeling Of The σ- And π...mentioning

confidence: 99%

“…The analysis of R CO versus R CC for 12 pentachlorophenol H-bond complexes gave the regression line R CO = −1.6R CC + 3.5 with a correlation coefficient = −0.941. Thus, it was concluded that, at least for pentachlorophenol complexes with N and O bases, the π-electron model of interactions is decisive …”

Section: 2 Intermolecular H-bond Systems and Modeling Of The σ- And π...mentioning

confidence: 99%

“…In the case of both pairs, proton transfer to the base leads to an increase of electronegativity of the proton-accepting site (oxygen and nitrogen atoms) and hence to a substantial change in the ipso angle; the Walsh−Bent rule works . In the case of bond lengths, the effect is associated not only with the changes in electronegativity but also, even to a greater extent, with the mesomeric effect, in other words, with a possibility of π-electron delocalization …”

Section: 4 Ab Initio Modeling Of the H-bond Effect On The Ring In The...mentioning

confidence: 99%

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Interrelation between H-Bond and Pi-Electron Delocalization

2005

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Proton transfer reaction in N‐methyl‐2‐hydroxy‐Schiff bases

Filarowski

Koll

Głowiak

et al. 1998

Ber Bunsenges Phys Chem

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The structure of two ortho‐hydroxy N‐methyl Schiff bases as well as the selfcondensation product of 2‐(N‐methyliminomethyl)‐phenol are determined by X‐Ray crystallography and by ab initio DFT, on B3LYP/6‐31G** level, calculations. Electronic coupling between acidic and basic centres of the molecules, especially effective in the proton transfer structure, is discussed on the basis of detailed analysis of differentiation of bond lengths both in aromatic and chelate rings. Consequences of this coupling on the intramolecular hydrogen bonding and proton transfer process are discussed.

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Crystallographic studies of intra- and intermolecular interactions Part VII. Crystal and molecular structure of the complex of acridine—pentachlorophenol: H-bonding effect on the geometry of the pentachlorophenol moiety

Cited by 17 publications

References 13 publications

Combined X-ray Diffraction and ¹⁵N CPMAS NMR Study of Molecular Structure and Proton Order/Disorder Phenomena in Cyclic N,N‘-Bisarylformamidine Dimers

Combined X-ray Diffraction and ¹⁵N CPMAS NMR Study of Molecular Structure and Proton Order/Disorder Phenomena in Cyclic N,N‘-Bisarylformamidine Dimers

Interrelation between H-Bond and Pi-Electron Delocalization

Proton transfer reaction in N‐methyl‐2‐hydroxy‐Schiff bases

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Crystallographic studies of intra- and intermolecular interactions Part VII. Crystal and molecular structure of the complex of acridine—pentachlorophenol: H-bonding effect on the geometry of the pentachlorophenol moiety

Cited by 17 publications

References 13 publications

Combined X-ray Diffraction and 15N CPMAS NMR Study of Molecular Structure and Proton Order/Disorder Phenomena in Cyclic N,N‘-Bisarylformamidine Dimers

Combined X-ray Diffraction and 15N CPMAS NMR Study of Molecular Structure and Proton Order/Disorder Phenomena in Cyclic N,N‘-Bisarylformamidine Dimers

Interrelation between H-Bond and Pi-Electron Delocalization

Proton transfer reaction in N‐methyl‐2‐hydroxy‐Schiff bases

Contact Info

Product

Resources

About

Combined X-ray Diffraction and ¹⁵N CPMAS NMR Study of Molecular Structure and Proton Order/Disorder Phenomena in Cyclic N,N‘-Bisarylformamidine Dimers

Combined X-ray Diffraction and ¹⁵N CPMAS NMR Study of Molecular Structure and Proton Order/Disorder Phenomena in Cyclic N,N‘-Bisarylformamidine Dimers