Resonance Effects in the Solvolysis of α-t-Butyl-α-neopentylbenzyl and α-t-Butyl-α-isopropylbenzyl p-Nitrobenzoates

Fujio, Mizue; Ohe, Makoto; Nakata, Kohei; Tsuji, Yutaka; Mishima, Masaaki; Tsuno, Yuho

doi:10.1246/bcsj.70.929

Cited by 10 publications

References 37 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

Ab initio MO study of benzylic cations. Part 3. Protonated benzoyl derivatives

Nakata

Fujio

Mishima

et al. 1998

J. Phys. Org. Chem.

View full text Add to dashboard Cite

Structures of α‐hydroxybenzylic cations and their conjugate bases, which cover a wide variation of stability, were optimized by means of ab initio molecular orbital method at the RHF/6–31G* level. Total energies were calculated at the MP2/6–31G*//RHF/6–31G* + ZPE (scaled 0.9) level. Calculated relative proton affinities of the respective neutral molecules (benzoyl compounds; conjugate bases of α‐hydroxybenzylic cations) agreed well with the corresponding basicities in the gas phase. The geometries of α‐amino‐α‐hydroxybenzyl and α‐hydroxy‐α‐dimethylaminobenzyl cations were also optimized at the fixed dihedral angles between the cationic 2pπ orbital and the benzene π orbital (ϕ), and between the cationic 2pπ orbital and lone pair electron orbital of the α‐substituent (θ). The changes in Wiberg bond orders and the rotational potentials about ϕ and θ showed that the degree of resonance interaction between the cationic center and phenyl ring is balanced by the electronic effects of α‐substituents in benzylic cations. The obtained theoretical indices of all parent cations such as Mulliken population, Wiberg bond order and bond lengths were correlated linearly with the resonance demand parameter (r value) which were given by the Yukawa–Tsuno substituent effect analysis in the gas phase and in aqueous solution. These relationships are consistent with those for other benzylic cations such as destabilized carbocations and sterically hindered cations studied previously. This confirms that the empirical r value has a definitive physical meaning, i.e. a measure of the resonance interaction between the cationic center and the aryl moiety. Copyright © 1998 John Wiley & Sons, Ltd.

show abstract

Ab initio MO study of benzylic cations. Part 3. Protonated benzoyl derivatives

Nakata

Fujio

Mishima

et al. 1998

J. Phys. Org. Chem.

View full text Add to dashboard Cite

show abstract

Substituent effects on the solvolysis of 1,1-diphenyl-2,2,2-trifluoroethyl tosylates. Part III. Effects of electron-donating substituents in the fixed aryl moiety

Fujio

Kim

Morimoto

et al. 1999

J. Phys. Org. Chem.

Self Cite

View full text Add to dashboard Cite

The solvolysis rates of 1-aryl-1-(p-methoxyphenyl)-2,2,2-trifluoroethyl and 1-aryl-1-(p-phenoxyphenyl)-2,2,2-trifluoroethyl bromides and chlorides were conductimetrically measured at 25.0°C in 80% aqueous ethanol. The solvolysis rates of 1-(p-methylphenyl)-fixed series were also set up to analyze the substituent effect. The substituent effects on these Y-series of solvolyses were analyzed on the basis of the Yukawa-Tsuno equation. The pmethoxyphenyl-fixed series showed a linear correlation with r = À1.7 and r = 1.0 for the substituent range less reactive than p-Me including all meta substituents, and a discrete correlation with r = À3.9 and r = 1.26 for the strong p-donor class substituents more reactive than p-PhO. A similar bilinear correlation was obtained for the Y = p-PhO series. The partial correlations for the strong p-donor class substituents in both Y-series are nearly the same as the correlation r = À4.2 and r = 1.2 for symmetrically disubstituted (X = Y) series. These bilinear (or non-linear) correlations were explicable in terms of changes in the coplanarity of the two benzene rings depending upon the resonance capabilities of X and Y substituents. For strong p-donor class X substituents as strongly p-electron donating as the Y substituent, both aryl rings are equivalently twisted as in the symmetrical X = Y series, and for less electrondonating X substituents, the fixed p-methoxyphenyl (or p-phenoxyphenyl) ring remains in a coplanar conformation and X-phenyl is twisted more out of coplanarity. In the fixed Y = p-Me series, a significantly non-linear correlation was found, comprising three distinct correlations characteristic of three conformers, a conformer with the X-aryl coplanar and Y-aryl twisted, a symmetrical conformer with X being a weak or moderate p-electron donor and both aryls being equivalently twisted, and a conformer with Y-aryl coplanar and X-aryl twisted. The relative stabilities of these conformers were estimated by the ab initio MO optimization of the mono-p-methoxycarbenium ion, confirming the conclusions above.

show abstract

Solvolysis of Highly Congested Tertiary Benzylic p‐Nitrobenzoates. Kinetic Probe for Detecting Resonance Contribution of Aryl Moiety to the Cationic Transition State

Liu

Chin

Kuo

2006

J Chinese Chemical Soc

View full text Add to dashboard Cite

The solvolysis of a series of 1‐aryl‐2,2‐dimethyl‐1‐phenyl‐1‐propyl p‐nitrobenzoates (6a‐6g) in a variety of solvents were studied. Both the single‐parameter Hammett‐Brown equation (Eqn. 1) and the dual‐parameter Yukawa‐Tsuno equation (Eqn. 2) showed excellent linear correlations, although inverse order of k(p‐CF3)/k(m‐CF3) was realized in five different solvent systems. A similar result was also found in 3‐aryl‐2,2,4,4‐tetramethyl‐3‐pentyl p‐nitrobenzoates (5) in 80% acetone. The result of Grunwald‐Winstein type correlation analysis against YBnOPNB or YxBnOPNB showed ambiguity for interpretation. It provides more evidence for the lack of coplanarity between the aryl ring and the sp2 plane at the cationic transition state, and thus an insignificant resonance contribution from the aromatic moiety. A comprehensive collection of published data is tabulated.

show abstract

Resonance Effects in the Solvolysis of α-t-Butyl-α-neopentylbenzyl and α-t-Butyl-α-isopropylbenzyl p-Nitrobenzoates

Cited by 10 publications

References 37 publications

Ab initio MO study of benzylic cations. Part 3. Protonated benzoyl derivatives

Ab initio MO study of benzylic cations. Part 3. Protonated benzoyl derivatives

Substituent effects on the solvolysis of 1,1-diphenyl-2,2,2-trifluoroethyl tosylates. Part III. Effects of electron-donating substituents in the fixed aryl moiety

Solvolysis of Highly Congested Tertiary Benzylic p‐Nitrobenzoates. Kinetic Probe for Detecting Resonance Contribution of Aryl Moiety to the Cationic Transition State

Contact Info

Product

Resources

About