Nobuaki Nishiyama

Nascent vibrational and rotational distributions of NH(A 3Π, c 1Π) in the dissociative excitation of NH3 by Ar(3P2,0) at thermal energy

The Ar(3P2,0)+NH3 reaction has been studied by optical emission spectroscopy. Experiments have been performed by using a flowing afterglow apparatus and a new low‐pressure apparatus. In the latter experiment the Ar(3P2,0) atoms generated by a microwave discharge were expanded into a high vacuum chamber through an orifice. Essentially the same results have been obtained from the two experimental systems. The NH(c 1Π–a 1Δ) emission as well as the NH(A 3Π–X 3∑−) emission was observed. The emission intensity ratio INH(c)/INH(A) was measured to be 0.31±0.03. The vibrational population ratio P(v’=1)/P(v’=0) for the NH(A 3Π) state was determined to be 0.35±0.05, while the effective rotational temperatures for the NH(A 3Π,v’=0) and NH(c 1Π,v’=0) states were estimated to be 2000±300 K and 1050±70 K, respectively. The observed vibrational and rotational distributions of the NH(A 3Π) state and the rotational distribution of the NH(c 1Π) state were much colder than those predicted from a simple statistical theory. Th...

Synthesis and crystallographic studies of a calix[4]arene with a 1,3-alternate conformation

25,27-Bis(ethoxycarbonylmethoxy)-26,28-bis(2-pyridylmethoxy)-5,11,17,23-tetra-tert-butylcalix[4]arene with a 1,3-alternate conformation (1,3-alternate-2) has been synthesized. Dynamic 1H NMR spectroscopy has established that the conformation is immobilized (i.e., the oxygen-through-the-annulus rotation is inhibited). The single crystal was grown from acetonitrile and analysed by X-ray crystallography. It was found that the structural characteristics of a 1,3-alternate conformation are (i) the four phenyl rings are more or less parallel to each other, the dihedral angles between the four phenyl rings and the mean plane of the four methylene groups being 93.5, 100.4, 101.4 and 106.1°, (ii) the ArCH2Ar bond angles are more expanded than those for other conformations and (iii) 1,3-alternate-2 in solution adopts C2 symmetry whereas in the solid state it is less symmetrical because of the unsymmetrical orientation of the ester and the pyridyl substituents. This is a rare example of the X-ray crystallographic analysis of 1,3-alternate calix[4]arenes.

Synthesis and characterization of dinuclear rhodium complexes containing (benzylthiomethyl)diphenylphosphine as the bridging ligand. Structure of the novel rhodium(II) complex [Rh2Cl4(CO)2(µ-PhCH2SCH2PPh2)2]

Treatment of [{RhCl(CO)2}2] with 5 equivalents of PhCH2SCH2PPh2(btmp) gave the mononuclear Vaska-type complex trans-[RhCl(CO)(btmp-P)2], whereas the reaction with 2 equivalents of btmp afforded not the expected face-to-face complex [Rh2Cl2(CO)2(µ-btmp)2] but the chloro-bridged complex [Rh2(µ-Cl)(CO)2(µ-btmp)2][RhCl2(CO)2]. The tetraphenylborate salt analogue [Rh2(µ-Cl)(CO)2(µ-btmp)2]BPh4 was obtained from the reaction of an ethanolic solution of [RhCl2(CO)2]– with 1 equivalent of btmp and NaBPh4. Treatment of [NBun4][RhCl2(CO)2] with 1 equivalent of btmp afforded the carbonyl-bridged dinuclear complex [Rh2Cl2(µ-CO)(µ-btmp)2], while the above reaction performed in the presence of hydrochloric acid gave the novel dinuclear rhodium(II) complex [Rh2Cl4(CO)2(µ-btmp)2](5). Complex (5) was also obtained from the reaction of an ethanolic solution of [RhCl2(CO)2]–and 1 equivalent of btmp. Crystals of (5) are monoclinic, space group C2/c, with a= 14.064(3), b= 19.364(4), c= 16.930(5)A, β= 116.67(2)°, and Z= 4; final R= 0.036 for 3 529 observed reflections. The structure shows that there is a metal–metal bond [Rh–Rh 2.733(3)A] and the two µ-btmp ligands are co-ordinated to rhodium atoms cis to each other with a head-to-tail arrangement. The relationships among the synthesized complexes are discussed.

Quasiclassical trajectory study of the reaction C(3P)+HI→CH(X 2Π) + I

Abstract Three-dimensional quasiclassical trajectory calculations have been performed for the C( 3 P) + HI/DI→CH (X 2 Π)/CD (X 2 Π) + I reactions by using LEPS potential energy surfaces. The experimental vibrational distribution of the product CH has been compared with the calculated one. It has been qualitatively suggested that the potential energy surface for the C + HI reaction is highly attractive, and that the smaller product vibrational energy disposal, 〈ƒ ν 〉, relative to those of the reactions of Cl, F, and O with HI is due to secondary encounters on its surface. This conclusion has been also supported by the calculated isotope effect on the product vibrational energy disposal for the C + HI/DI reactions.

Preparation and structural properties of hydroxy- and alkoxy-[2.2.1]metacyclophanes

The asymmetric 4a and symmetric conformers 4b of a trimethoxy[2.2.1]metacyclophane were isolated and the structures were established by 1H NMR spectroscopy and X-ray crystallography. The trihydroxy[2.2.1]-5 and dihydroxy(methoxy)[2.2.1]metacyclophane 6 were obtained by demethylation of isomers 4a and 4b, respectively. Treatment of compound 5 with ethyl bromoacetate afforded only the tris(ethoxycarbonylmethoxy)[2.2.1]metacyclophane 7. On the other hand the bis(ethoxycarbonylmethoxy)(methoxy)[2.2.1]-8 and ethoxycarbonylmethoxy(hydroxy)(methoxy)[2.2.1]metacyclophane 9 were obtained from compound 6. It was found that compounds 4a and 7 assume a ‘2,1-alternate’ conformation, whereas, on the other hand, compounds 4b, 6, 8 and 9 have a ‘2,2-alternate’ conformation. In the case of compound 5 both ‘2,1-alternate’ and ‘2,2-alternate’ conformers were detected by 1H NMR spectroscopy. The chiralities of compounds 4a and 9 were confirmed by their 1H NMR spectrum in the presence of Pirkles reagent.

Structure of 3-Chlorotropolone

C7H5C102, Mr = 156.6, monoclinic, P21/c, a = 8.476 (2), b = 12.241 (2), c = 8.170 (2) A, /3 -- 126.47 °, V= 681.7 A 3, z = 4, Dx = 1.525 g cm -3, A(Cu Ka) = 1.54184 A, /z = 44.63 cm-~, F(000) = 320, T = 293 K, R -- 0.046 for 833 reflections with I > 3tr(I). The hydroxylic proton forms a bifurcated hydrogen bond with carbonyl O atoms, one branch intramolecular and the other intermolecular. The latter intermolecular branches form a hydrogen- bonded dimer, which is roughly planar. Introduction. The structures of tropolone and some tropolone derivatives have been studied. It has been shown that 5,isopropyltropolone (Berg, Karlasson, (P~.tti & Wiehager, 1976) as well as tropolone manouchi & Sasada, 1973) forms a bifurcated hydrogen bond with the carbonyl O atoms, one branch being intramolecular and other intermolecu- lar. On the other hand, 4-isopropyltropone does not form a dimer, but O...O hydrogen bonds of 2.8 A link the molecules in a chain (Derry & Hamor, 1972). Very recently, we have measured the electronic spectra of the isolated 3-chlorotropolone (Tsuji, Sekiya, Nishimura, Mori & Takeshita, 1991) and 3-bromotropolone (Sekiya, Sasaki, Nishimura, Mori & Takeshita, 1990). The observation of tunnel splitting provides conclusive evidence for the de- localization of the proton. We have found that the hydroxylic proton is delocalized in 3-chlorotro- polone, whereas the proton is localized in 3- bromotropolone. It has been suggested that the localization of the hydroxylic proton strongly depends on the planarity of the molecule. In order to examine the effect of the substitution of a C1 atom on the molecular and crystal structure, an X-ray

Laser-induced fluorescence study on reactions of C+(2P) and C(1D,1S) with alcohols leading to CH(X2π) radicals at thermal energy

Thermal energy reactions of C+(2P) and C(1D,1S) with CH3OH, C2H5OH, n-C3H7OH and i-C3H7OH to give CH(X2Π) radicals have been investigated by observing laser-induced fluorescence (LIF) spectra of CH(A—X) in a flowing afterglow. In the hydride ion abstraction by C+(2P), only CH3OH exhibited the CH(A—X) LIF spectrum with a vibrational distribution of 1.0 : 0.62 for v″ = 0 and 1, respectively. On the other hand, the CH(A—X) LIF spectra exclusively from v″ = 0 were observed in the reactions of C(1D,1S) with all alcohols studied. By isotopic substitution for CH3OH it was shown that the CH(X) radicals arise from the selective attack on the methyl site in the reactions of C+(2P) and C(1D,1S) with methanol.

Novel Second Harmonic Generation from Intermolecular Charge-Transfer Complexes of Styrylpyridinium Salts in the Crystalline State

Abstract Novel second harmonic generation (SHG) was observed from the crystalline powder of the ion-pair charge-transfer (CT) complexes consisting of 1-methyl-4-(4-nitrostyryl)pyridinium as an acceptor and tetraphenylborate as a donor. The second harmonic light intensity dramatically decreased upon excitation of a CT band due to the photoinduced electron transfer from tetraphenylborate to styrylpyridinium moiety. These results strongly suggested that the CT transition in the ion-pair complexes would cause SHG. The crystalline structure of an ion-pair CT complex of 1-methyl-4-(4-cyanostyryl)pyridinium tetraphenylborate which also exhibited strong SHG was investigated to elucidate the mechanism of the SHG in the ion-pair CT complex system.

Isolation, characterization, and demethylation by BBr3 of two conformers of 8,15,23-trimethoxy[2,2.1]metacyclophane

Two conformers, (5A) and (5B), of trimethoxy[2.2.1]metacyclophane have been separated and characterized by 1H NMR spectroscopy, X-ray crystallography, and demethylation.

Internal energy disposal in the chemiluminescent reaction CD + NO → ND(A) + CO and the kinetic isotope effect

Abstract The vibrational and rotational energy disposal for ND(A) from the CD + NO reaction was measured in a flowing afterglow. The initial vibrational and rotational distributions of ND(A) were obtained from a spectral simulation. The initial vibrational distribution was (0.51 ± 0.05) ν′ = 0 : (0.26 ± 0.05) ν′ = 1 : (0.16 ± 0.05) ν′ = 2 : (0.07 ± 0.05) ν′ = 3 . The rotational temperatures in ν′ = 0, 1, 2 and 3 levels were 4500 ± 500, 4000 ± 500, 4000 ± 500 and 4000 ± 500 K, respectively. The fractions of the available energy deposited into the vibration, 〈 f v 〉 and rotation, 〈 f R 〉, were 0.21 and 0.36, respectively. The results for ND(A) were compared with those for NH(A) from the CH + NO reaction reported previously and the reaction dynamics was discussed on the basis of the observed isotope effect on the energy state distributions. The kinetic isotope effect k H / k D in the CH, CD + NO reactions was measured to be 1.84 ± 0.23. The experimental result was compared with a theoretical calculation using transition-state theory.