Kazuhide Nakata

Ab initio MO study of benzylic cations?1. Some theoretical parameters related to the resonance demand in the Yukawa-Tsuno equation

Structures of 14 kinds of benzylic cations into which are introduced various substituents at benzylic position were optimized by means of the ab initio molecular orbital method at the RHF/6-31G* level. The theoretical indices obtained associated with the resonance interaction, such as population, bond order and bond length, were compared with the resonance demand parameter (r value) of corresponding solvolysis systems that were given by the Yukawa-Tsuno substituent effect analysis. The r value was linearly correlated with the theoretical resonance indices.

Substituent effect on the solvolysis of α-t-butyl-α-methylbenzyl chlorides

Abstract The substituent effect on the solvolysis rates of α-t-butyl-α-methylbenzyl chlorides in 80% aq. acetone was correlated to give ϱ=−4.3 and r=0.91 in terms of the LArSR Eq. (1). This slightly reduced r value relative to full conjugation corresponds to a deviation by θ=24.5° from the coplanarity of the benzylic π-system.

Substituent effect on the solvolysis of 2,2-dimethylindan-1-yl chlorides

Abstract The substituent effect on the solvolysis of 2,2-dimethylindan-1-yl chlorides was analyzed in terms of the LArSR Eq., to give ϱ=−5.81 and r=1.14. The coplanarity of α-t-butylbenzyl cation system was discussed.

Separation of the energetic and geometric contributions to aromaticity. Part VI. Changes of the aromatic character of the rings in naphthalene, anthracene, phenanthrene and pyrene derivatives induced by the charged substituent CH2+

Ab initio 6-31G∗ optimised geometries of naphthalene, anthracene, phenanthrene, pyrene and all their CH2+ mono-substituted derivatives have been examined in respect to estimate the changes of their aromatic character due to these kinds of substitution. CH2+ substituent attached to aromatic hydrocarbons causes dramatic changes in their molecular geometry. This implies great changes in both local (i.e. referring to a single ring) and global aromaticity. The substituted rings always lose some part of their original aromatic character, but if the position of the substitution permits formation of the quinoidal structure via a short CC bond which is spread over the larger part of the molecule, the decrease of aromatic character is greater than in the other cases. Formation of quinoidal structures in a molecule leads to a long-range intramolecular charge transfer.

The importance of resonance stabilization in the benzylic solvolysis. Substituent effects on the solvolysis of α,α-diisopropylbenzyl chlorides

The substituent effect on the solvolysis of α,α-diisopropylbenzyl chlorides can be described in terms of σ+ value. No significant steric loss of resonance was observed by introducing two bulky isopropyl groups into benzylic reaction center.

Computational study of the substituent effects on the gas-phase stabilities of phenylboranylmethyl anions

Abstract The relative gas-phase stabilities of ring-substituted phenylboranylmethyl anions were computationally determined using isodesmic reactions. The energies of species included in the reactions were calculated at the B3LYP/6-311+G(2d,p) level of theory. The obtained substituent effects were analyzed by the extended Yukawa-Tsuno equation, and unexpectedly substantial r− (0.59) and s (0.65) values were found for the fully-optimized planar anion. The substantial through-resonance effect quantified by the r− value was observed, although it is not possible to draw a canonical form in which the negative charge is delocalized on the benzene ring. Substituent effects were also analyzed for the anions in which the dihedral angle (φ) between the side chain plane and the benzene ring was fixed. The r− value decreased significantly by changing the φ from 0° to 90°, while the s value changed little. NBO analyses revealed that the r− value is proportional to the sum of the π–π* and σ–π* orbital interactions between the side chain and the benzene ring. This fact shows that the through-resonance effect quantified by the r− value is present at all φ, and therefore, the anion cannot become an ideal σ0-reference system. The constant saturation effect quantified by the s value can be explained by the constant charge distributed to the benzene ring. The combination of substituent-effect analysis and NBO analysis successfully revealed the nature of the anion.