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Titolo:
Molecular structure and torsional potential of trans-azobenzene. 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:
1089-5639(20011018)105:41<9347:MSATPO>2.0.ZU;2-0
Fonte:
ISI
Lingua:
ENG
Soggetto:
DENSITY-FUNCTIONAL THEORY; AB-INITIO CALCULATIONS; VIBRATIONAL FREQUENCIES; LIQUID-CRYSTALS; RAMAN-SPECTRA; FORCE-FIELDS; 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 trans-azobenzene. A gas electron diffraction study", J PHYS CH A, 105(41), 2001, pp. 9347-9353

Abstract

The molecular structure of trans-azobenzene (Ph-N=N-Ph) has been determined by gas electron diffraction. Diffraction patterns were taken at 407 K anddata analysis was made using the structural constraints obtained from MP2/6-31+G* calculations. Vibrational mean amplitudes and shrink-age 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){V-2(1 - cos 2 phi (i))/2 + V-4(1 - cos 4 phi (i))/2}, where phi (i) denotes the torsional angle around each N-C 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 (V-2 and V-4/kcal mol(-1)) and principal structure parameters (r(g)/Angstrom, angle (alpha)/deg) with the estimated limits of error (3 sigma) are as follows: V-2 = 1.7(6); V-4 = 0.6(13); r(N=N) = 1.260(8); r(N-C) = 1.427(8); <r(C-C)> = 1.399(l); <r(C-H)> = 1.102(7); angle NNC = 113.6(8); (angle NCCcis - angle NCCtrans)/2 = 5.0(9), where < > means an average value and C-cis and C-trans denote the carbon atoms cis andtrans to the N=N bond, respectively. Thus, the stable form was found to beplanar with C-2h Symmetry. The observed structure was compared with those of trans-azoxybenzene (Ph-N(-O)=N-Ph) and trans-stilbene (Ph-CH=CH-Ph). Thestability of the liquid crystals with these types of molecular cores was discussed on the basis of the gas-phase structures of the model compounds ofcores. Nearly the same results were obtained in the data analysis using the constraints from RHF/6-31G** ab initio calculations.

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Documento generato il 10/07/20 alle ore 07:14:57