A CNDO/2 Study of Bipyridyls. I.

Borgen, O.; Mestvedt, Brynhild; Skauvik, Inge; Andresen, Arne F.; Sandström, M.

doi:10.3891/acta.chem.scand.30a-0043

Cited by 22 publications

(2 citation statements)

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“…From bpy it is known that the first protonation changes the conformation from trans to cis . The proton is shared between both nitrogen atoms 8–10. The second protonation leads again to a trans ‐conformation.…”

Section: Resultsmentioning

confidence: 99%

Protonation Behaviour of Chiral Tetradentate Polypyridines Derived from α‐Pinene

Düggeli

Christen

Zelewsky

2004

Chemistry A European J

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Detailed protonation experiments of the [5,6]-pinenebipyridine molecule and the unsubstituted [4,5]- and [5,6]-CHIRAGEN[0] ligands in various solvents indicate a variety of structures of the protonated species. UV-visible and NMR measurements (including (15)N chemical shifts) show the transition from trans to cis conformation of [5,6]-pinenebipyridine upon protonation. The [4,5]-CHIRAGEN[0] ligand, in which the protonation sites of the nitrogen atom donors are at opposite sides of the molecule, behave essentially like two independent bipyridine moieties; this behaviour was monitored by UV-visible, CD and NMR spectroscopy (including (15)N data). In the case of the [5,6]-CHIRAGEN[0], a pocket of donor atoms provides a chiral environment for two protons per ligand.

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Section: Resultsmentioning

confidence: 99%

Protonation Behaviour of Chiral Tetradentate Polypyridines Derived from α‐Pinene

Düggeli

Christen

Zelewsky

2004

Chemistry A European J

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“…[26] However, NMR-and IR data seem to indicate a planar s-trans conformation of the DAD backbone also in solution. [27,28] .…”

Section: Solid-state Structuresmentioning

confidence: 99%

2,3-Dialkynyl-1,4-diazabuta-1,3-dienes as Novel π-Systems: Synthesis, Structure, and Electronic Properties

Faust¹,

Göbelt

Weber

et al. 1999

Eur. J. Org. Chem.

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The introduction of alkynyl groups into the 2,3‐positions of the 1,4‐diazabuta‐1,3‐diene (DAD) backbone succeeds along two complementary synthetic routes either by condensing triisopropylsilyl‐terminated dialkynyl‐1,2‐diones with primary aromatic amines or by a palladium‐mediated alkynylation of bis(imidoyl chlorides). X‐ray crystallographic analyses of two dialkynyl DAD derivatives reveals their planar (E‐s‐trans‐E) conformations in the solid state. However, the central CC bond of both DAD backbones investigated has a length of 1.491(2) Å, and is therefore too long to indicate efficient delocalization across the DAD core. The UV/Vis spectra of dialkynyl DADs demonstrate that their absorptions in comparison to those of non‐alkynyl DADs are bathochromically shifted by more than 40 nm, thereby demonstrating the suitability of the title compounds for developing NIR chromophores. The electron absorption properties of differentially N,N′‐disubstituted dialkynyl DADs gave no indication for a push‐pull effect across the DAD skeleton and suggest the ynimine moiety as the active chromophore of dialkynyl DADs. The electrochemical properties of the title compounds were determined by cyclo‐ and steady state voltammetry and show that introducing alkynyl groups leads to more easily reducible DAD systems. Again, the perception of dialkynyl DADs as covalently linked, but electronically decoupled ynimine units is corroborated by the redox potential of a differentially N,N′‐disubstituted dialkynyl DAD. Similar conclusions were drawn from semiempirical MO (PM3) calculations of dialkynyl DADs.

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The flexibility of biphenyl and related species utilizable as molecular swivels in rodlike polymers. A CNDO/2 analysis

Welsh¹,

Jaffé²,

Kondo³

et al. 1982

Makromol. Chem.

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~M~~~:Aromatic heterocyclic polymers are exceedingfy attractive high performance materids because of their unusudiy high mechanical strength, chemieaf resistance and thermal stability, but are very difficult to process unless "swivel" atoms or groups are inserted along the chains to increase conformational flexibility. The present theoretical investigation employs the CNDO/2 method with direct geometry o p t i m~~t i o n to cdculate such flexibifity for the wbHy aromatic swivefs biphenyi, 2,2 '-bipyridyf, 2 -~h e n y l~y~~n e , ~,~' -~p y r i m i d y~, and ~~pheny~pyrimi~ne. The most important result is the prediction that both flexibility and accessibility of coplanar ~n f o r m~t i~n s shouid increase s i~~c~~~y with the number of ortrrr0-CI-I groups replaced by N-atoms. The calculations also provide information on other conformation-dependent p r o p erties such as optimized geometries, charge distributions, and dipole moments, and these results are found to be in satisfactory agreement with the results of previous theoretical and experimental studies. Finally, since these chains are soluble only in strongly acidic media, the species mono-and diprotonated 2,2 '-bipyridyl, 2,2'-bipyridyl* H@+, and 2,2 '-bipyrimidyl* 2H20were Stso investigated with regard to some of these c o~f~~a t i o n a~ c h~~c~r i~t i~s .

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A CNDO/2 Study of Bipyridyls. I.

Cited by 22 publications

References 0 publications

Protonation Behaviour of Chiral Tetradentate Polypyridines Derived from α‐Pinene

Protonation Behaviour of Chiral Tetradentate Polypyridines Derived from α‐Pinene

2,3-Dialkynyl-1,4-diazabuta-1,3-dienes as Novel π-Systems: Synthesis, Structure, and Electronic Properties

The flexibility of biphenyl and related species utilizable as molecular swivels in rodlike polymers. A CNDO/2 analysis

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