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Titolo: Molecular structure and torsional potential of transazobenzene. A gas electron diffraction study
Autore: Tsuji, T; Takashima, H; Takeuchi, H; Egawa, T; Konaka, S;
 Indirizzi:
 Hokkaido Univ, Grad Sch Sci, Div Chem, Sapporo, Hokkaido 0600810, Japan Hokkaido Univ Sapporo Hokkaido Japan 0600810 oro, Hokkaido 0600810, Japan
 Titolo Testata:
 JOURNAL OF PHYSICAL CHEMISTRY A
fascicolo: 41,
volume: 105,
anno: 2001,
pagine: 9347  9353
 SICI:
 10895639(20011018)105:41<9347:MSATPO>2.0.ZU;20
 Fonte:
 ISI
 Lingua:
 ENG
 Soggetto:
 DENSITYFUNCTIONAL THEORY; ABINITIO CALCULATIONS; VIBRATIONAL FREQUENCIES; LIQUIDCRYSTALS; RAMANSPECTRA; FORCEFIELDS; STILBENE; ENERGY; APPROXIMATION; MESOGEN;
 Tipo documento:
 Article
 Natura:
 Periodico
 Settore Disciplinare:
 Physical, Chemical & Earth Sciences
 Citazioni:
 40
 Recensione:
 Indirizzi per estratti:
 Indirizzo: Konaka, S Hokkaido Univ, Grad Sch Sci, Div Chem, Sapporo, Hokkaido 0600810, Japan Hokkaido Univ Sapporo Hokkaido Japan 0600810 ido 0600810, Japan



 Citazione:
 T. Tsuji et al., "Molecular structure and torsional potential of transazobenzene. A gas electron diffraction study", J PHYS CH A, 105(41), 2001, pp. 93479353
Abstract
The molecular structure of transazobenzene (PhN=NPh) has been determined by gas electron diffraction. Diffraction patterns were taken at 407 K anddata analysis was made using the structural constraints obtained from MP2/631+G* calculations. Vibrational mean amplitudes and shrinkage corrections were calculated from the harmonic force constants given by a normal coordinate analysis. Vibrational mean amplitudes were refined as groups. The torsion of each phenyl ring was treated as a large amplitude vibration. The potential function for torsion was assumed to be V(phi (1),phi (2)) = Sigma (i=1,2){V2(1  cos 2 phi (i))/2 + V4(1  cos 4 phi (i))/2}, where phi (i) denotes the torsional angle around each NC bond. Quantum mechanical calculations were performed by taking account of two torsional motions to derive a probability distribution function, P(phi (1),phi (2)). Because P(phi (1),phi (2)) = N exp(V(phi (1),phi (2)/kT) was found to be a good approximation at 407 K where N is a constant, it was adopted in the data analysis. The determined potential constants (V2 and V4/kcal mol(1)) and principal structure parameters (r(g)/Angstrom, angle (alpha)/deg) with the estimated limits of error (3 sigma) are as follows: V2 = 1.7(6); V4 = 0.6(13); r(N=N) = 1.260(8); r(NC) = 1.427(8); <r(CC)> = 1.399(l); <r(CH)> = 1.102(7); angle NNC = 113.6(8); (angle NCCcis  angle NCCtrans)/2 = 5.0(9), where < > means an average value and Ccis and Ctrans denote the carbon atoms cis andtrans to the N=N bond, respectively. Thus, the stable form was found to beplanar with C2h Symmetry. The observed structure was compared with those of transazoxybenzene (PhN(O)=NPh) and transstilbene (PhCH=CHPh). Thestability of the liquid crystals with these types of molecular cores was discussed on the basis of the gasphase structures of the model compounds ofcores. Nearly the same results were obtained in the data analysis using the constraints from RHF/631G** ab initio calculations.
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Documento generato il 10/07/20 alle ore 07:14:57