Tsutomu Minato

Molecular orbital study on the gas-phase nucleophilic displacement on acyl chlorides

On etudie les reactions suivantes: F − +CH 3 COCl→CH 3 COF+Cl − et Cl − +CH 3 COCl→CH 3 COCl+Cl −

A Mechanistic Study of a Gas-Phase Ion/Molecule Reaction between CH2NH2+ and CH4

A gas-phase ion/molecule reaction starting from (CH4+ and N2O)/(CH4 and N2O+) is studied using a pulsed-discharge high-pressure mass spectrometer and the ab initio MO calculation. Two dominant ions, C2H6N+ and C3H8N+, are recognized; they are formed by the methylation of CH4N+. The C2H6N+ is formed via the following two reactions:CH2NH2+(or CH3NH+)+CH4 → (CH3)2NH2+ (5)(CH3)2NH2+ → CH3NHCH2++H2 (7)The methylation is composed of the heterolytic CH3+–H− addition to the C=N bond of CH4N+ and the subsequent H2 elimination. The growth of the ion by the methylation is largely exothermic, while the H2 elimination has a large energy barrier on the potential energy surface.A gas-phase ion/molecule reaction starting from (CH4+ and N2O)/(CH4 and N2O+) is studied using a pulsed-discharge high-pressure mass spectrometer and the ab initio MO calculation. Two dominant ions, C2H6N+ and C3H8N+, are recognized; they are formed by the methylation of CH4N+. The C2H6N+ is formed via the following two reactions:CH2NH2+(or CH3NH+)+CH4 → (CH3)2NH2+ (5)(CH3)2NH2+ → CH3NHCH2++H2 (7)The methylation is composed of the heterolytic CH3+–H− addition to the C=N bond of CH4N+ and the subsequent H2 elimination. The growth of the ion by the methylation is largely exothermic, while the H2 elimination has a large energy barrier on the potential energy surface.

Experimental and Theoretical Analyses of Azulene Synthesis from Tropones and Active Methylene Compounds: Reaction of 2-Methoxytropone and Malononitrile

A representative azulene formation from an active troponoid precursor (2-methoxytropone) and an active methylene compound (malononitrile) has been analyzed both experimentally and theoretically. (2)H-Tracer experiments using 2-methoxy[3,5,7-(2)H(3)]tropone (2-d(3)) and malononitrile anion give 2-amino-1,3-dicyano[4,6,8-(2)H(3)]azulene (1-d(3)) in quantitative yield. New and stable (2)H-incorporated reaction intermediates have been isolated, and main intermediates have been detected by careful low-temperature NMR measurements. The detection has been guided by mechanistic considerations and B3LYP/6-31(+)G(d) calculations. The facile and quantitative one-pot formation of azulene 1 has been found to consist of a number of consecutive elementary processes: (a) The troponoid substrate, 2-methoxytropone (2), is subject to a nucleophilic substitution by the attack of malononitrile anion (HC(CN)(2)(-)) to form a Meisenheimer-type complex 3, which is rapidly converted to 2-troponylmalononitrile anion (5). (b) The anion 5 is converted to an isolable intermediate, 2-imino-2H-cyclohepta[b]furan-3-carbonitrile (6), by the first ring closure in the reaction. (c) A nucleophilic addition of the second HC(CN)(2)(-) toward the imine 6 at the C-8a position produces the second Meisenheimer-type adduct 7. (d) The second ring closure leads to 1-carbamoyl-1,3-dicyano-2-imino-2,3-dihydroazulene (11). A base attacks the imine 11, which results in generation of a conjugate base 12 of the final product, azulene 1.

Norcaradiene intermediates in mass spectral fragmentations of tropone and tropothioneElectronic supplementary information (ESI) available: reaction paths supporting Figs. 3–6. See http://www.rsc.org/suppdata/p2/b1/b102127n/

The fragmentation of mass spectroscopy of tropone (1) was compared with that of tropothione (2). The electron-impact mass spectroscopy of 1 afforded almost exclusively the benzene cation radical (m/z = 78). Mass spectroscopy of 2 gave similarly the m/z = 78 base peak along with an unusual (M+ − 1) peak. This hydrogen elimination was found to occur at the C(α)–H bond by the use of a 2H-labeled analogue of 2. Ab initio calculations (UB3LYP/6-31G*) showed that a π cation radical of 1 and a σ cation radical of 2 were converted to norcaradiene intermediates. Their further isomerizations led to [the benzene cation radical (m/z = 78) + CO] and [(m/z = 78) + CS], respectively. The fragmentation channel of 1 was calculated to have sufficiently small activation energies of intervening transition states to give almost exclusively the m/z = 78 peak. For a σ radical of 2, an α hydrogen moved to the sulfur atom. The resultant thiol was isomerized to a second norcaradiene and its further isomerization led to a thioketene like cation and a hydrogen atom corresponding to the unusual (M+ − 1) peak. The difference in fragmentation patterns of 1 and 2 is discussed in terms of their electronic structures.

Dual one-centre frontier-orbital interactions in [2 + 2] cycloadditions of ketenes

Dual one-centre frontier–orbital interactions are found to control the paths of cycloadditions of ketene to ethylene, methylenimine and formaldehyde by the analysis of the intrinsic reaction coordinates calculated with the MP2/6-31G* basis set.

Ab initio structures of transition states in electrophilic addition reactions of molecular halogens with ethene

The fluorination of ethene occurs via a four-centred transition state, while chlorination and bromination give zwitterionic three-centred transition states.

A theoretical comparison of SN1 and SN2 reactions of saturated alkyl chlorides

The mechanistic difference between bimolecular (SN2) and unimolecular (SN1) nucleophilic substitutions of saturated alkyl chlorides is investigated with ab initio molecular orbital (MO) calculations. The t-butyl substrate undergoes early (almost spontaneous) C–Cl bond scission, which may give double OH–(reagent) co-ordination on the carbonium cation. However, the symmetrically solvated ion, which has been accepted as a stable intermediate for racemization, is found to be located at the energy maximum of the OH– exchange reaction. The origin of racemization in nucleophilic substitution is discussed on the basis of the calculated potential surface.

Molecular-orbital study of the gas-phase reactions between methyl formate and the fluoride ion

An ab initio MO calculation with the 4-31G basis set is carried out on the gas-phase reaction between the fluoride ion and methyl formate. The minimum-energy paths of two channels F–+ HCOOCH3→ CH3OHF–+ CO (1), F–+ HCOOCH3→ HCOO–+ CH3F (2), are investigated by the geometry optimization. For (1) and (2), two and one intermediates are generated, respectively. The reactivity of the fluoride ion toward the carbonyl site is discussed with reference to the presence or the absence of a solvent effect.