ZfN: Search Results

1	Author	K. Figueroa, A., M. Campos-Vallette, R. Contreras, R.	Requires cookie*
	Title	A Theoretical Analysis of the Contributions to the Internal Rotation Barrier in N-Benzylideneanilines
	Abstract	An analysis, using CNDO wave functions, has been carried out on the different contributions to the internal rotation barrier in N-benzylideneaniline (1) and p-dimethylaminobenzylidene-p-nitro-aniline (2) in several conformations. The stability of the different structures has been expressed in terms of a partition of the total energy into electronic, net charges and steric hindrance contributions. Based on the shape of the total energy surface it appears that the barrier composition may be reasonably well described without approaching the absolute minimum. Rotation of the aniline group in both molecules is mainly governed by steric hindrance. Rotation of the benzylidene group shows a prevalent destabilizing electronic effect. The donor strength of the substituent in the benzylidene ring seems to play an important role in stabilizing a less nonplanar structure.
	Reference	Z. Naturforsch. 45a, 1199—1204 (1990); received July 4 1990
	Published	1990
	Keywords	N-benzylideneanilines, Semiempirical calculation, Energy partition and internal rotation
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	TEI-XML for	default:Reihe_A/45/ZNA-1990-45a-1199.pdf
	Identifier	ZNA-1990-45a-1199
	Volume	45

2	Author	C. Margheritis, C. Sinistri	Requires cookie*
	Title	/?-cyclodextrine and Water: Semiempirical Calculations
	Abstract	AMI and PM3 calculations were carried out on ß-cyclodextrine (ß-CD) undecahydrate in the experimental conformation at 120 K. The calculated /TCD/water interaction energies are very small and indicative for each water molecule of an unfavorable condition in respect to that of pure water. The conformationally optimized system was also studied: ß-CD appears highly symmetrical with negligible dipole moment, mainly because of the circular arrangement of the single vectors. Primary hydroxyls can easily rotate, while the secondary ones are stabilized by heteroannular hydrogen bonds and homoannular electrostatic interactions due to the consequent increase of the atomic charges. The ß-CD/water interaction energies in the optimized hydrated system are not significantly different from the experimental ones. This almost hydrophobic character is also shown by MM equilibrated solutions: all water molecules are rejected beyond 2.4 A; between 2.4 and 2.9 A highly structured water is present. From a purely enthalpic standpoint the molecule hydration appears highly improbable, thus the formation of ß-CD 11 H 2 0 must involve a compensation mechanism.
	Reference	Z. Naturforsch. 51a, 950—956 (1996); received May 13 1996
	Published	1996
	Keywords	ß-cyclodextrine hydrate, Semiempirical calculations, Water interactions
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	TEI-XML for	default:Reihe_A/51/ZNA-1996-51a-0950.pdf
	Identifier	ZNA-1996-51a-0950
	Volume	51

3	Author	Hans Bocka, Sabine Nicka, ChristianN. Äthera, JanW. Bats3, Professor Franz-Gustav	Requires cookie*
	Title	Strukturen ladungsgestörter Moleküle, 47 [1 , 2 ] Dinatrium-und Dikalium-Nitranilate: Die Cyanin-Verzerrung der Kohlenstoff-Sechsringe Structures of Charge-Perturbed Molecules 47 [1,2] Disodium and Dipotassium Nitranilates: The Cyanine Distortion of the Six-Membered Carbon Ring
	Abstract	Crystals of lemon yellow dipotassium nitranilate and of yellow disodium nitranilate di hydrate have been grown and their structures determined at 290 and 200 K. The six-member-ed, 0 2N-disubstituted rings show a pronounced cyanine distortion with all four CO bonds identical and the two (0 C C (N 0 2) C 0) e chains connected by single CC bonds of each 156 pm length. In the anhydrous K® salt, the ring is planar, but in the Na® hydrate salt it exhibits a twist conformation. Quantum chemical calculations allow to reproduce the structure in every detail, demonstrate strong charge alternation along the cyanine chains with considerable delocalization into the 0 2N acceptor substituents, and suggest that the rather long connecting CC bonds contain positively charged carbon centers on both ends. In addition, metal ion coordination effects as well as the rather high pKa value of nitranilic acid are rationalized.
	Reference	Z. Naturforsch. 49b, 1021—1030 (1994); eingegangen am 17. März 1994
	Published	1994
	Keywords	Cyanine Distortion of C6-Rings, Single Crystal Structures, Semiempirical Calculations
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	TEI-XML for	default:Reihe_B/49/ZNB-1994-49b-1021.pdf
	Identifier	ZNB-1994-49b-1021
	Volume	49