Yuho Tsuno

The Yukawa-Tsuno Relationship in Carbocationic Systems

Publisher Summary This chapter deals with reactions involving carbocationic transition states, in most cases forming intermediates having carbocationic centers at the conjugative position in the side chain. Yukawa–Tsuno (Y–T) introduced the concept of the varying resonance demand of reactions into substituent effect analysis. Nevertheless, the correlation results were always compared with those of the Brown equation implying constant resonance demand. The Y–T equation has been used extensively in studies of electrophilic substitution in the aromatic ring, and aliphatic nucleophilic substitution and related reactions forming a carbocation or a carbocationic (electron-deficient) center at the conjugative position (mostly benzylic position) in the side chain. The Y–T equation has proved to be one of the most fundamental and essential equations for understanding structure–reactivity relationships in chemical reactions using the language of the physical organic chemist.

Microwave spectra of 13CH3 12CD3 and 12CH3 13CD3 and the C–C bond length of ethane

We observed the J=2←1, K=1 transitions of two doubly labeled ethanes 13CH3 12CD3 and 12CH3 13CD3, which were contained in natural abundance in a CH3CD3 sample. The measured frequencies were subsequently made more accurate using enriched samples. Assuming the centrifugal distortion constants DJ and DJK, which were determined for 12CH3 12CD3, we calculated the B0 constants to be 16 088.428±0.030 and 16 251.914±0.030 MHz for 13CH3 12CD3 and 12CH3 13CD3, respectively. By combining these with the B0 of 12CH3 12CD3(16 474.438±0.030 MHz), we derived the rs distance of C–C to be 1.526131±0.000083 A, where the error was due to uncertainties of the rotational constants. We also calculated the rz(C–C) distance to be 1.5312 A in 12CH3 12CD3 by transferring Kuchitsu’s rz(C–H), rz(C–D), ϑz(CCH), and ϑz(CCD). We evaluated the dipole moments of the two species from the Stark effects to be 0.01067±0.00010 D and 0.01094±0.00011 D for 13CH3 12CD3 and 12CH3 13CD3, respectively, which were to be compared with 0.01078±0.00009 ...

Gas phase substituent effects. Stabilities of 1-aryl-2,2,2-trifluoroethyl cations

Abstract Gas-phase stabilities of 1-aryl-2,2,2-trifluoroethyl cations were determined based on chloride-transfer equilibria. The substituent effect was analyzed based on the LArSR Eq., giving a remarkably high r of 1.53 and a ϱ of −14.6.

Structure–reactivity correlations in nucleophilic substitution reactions of Y-substituted phenyl X-substituted benzoates with anionic and neutral nucleophiles

A kinetic study is reported for the reactions of 4-nitrophenyl X-substituted benzoates (1a-1) and Y-substituted phenyl benzoates (2a-1) with two anionic nucleophiles (OH(-) and CN(-)) and three amines (piperidine, hydrazine, and glycylglycine) in 80 mol% H(2)O-20 mol% dimethyl sulfoxide (DMSO) at 25.0 +/- 0.1 degrees C. Each Hammett plot exhibits two intersecting straight lines for the reactions of 1a-1 with the anionic nucleophiles and piperidine, while the Yukawa-Tsuno plots for the same reactions are linear. The Hammett plots for the reactions of 2a-1 with hydrazine and glycylglycine demonstrate much better linear correlations with sigma(-) constants than with sigma degrees or sigma constants, indicating that the leaving group departure occurs at the rate determining step (RDS). On the contrary, sigma(-) constants result in poorer Hammett correlation than sigma degrees constants for the corresponding reactions with OH(-) and CN(-), indicating that the leaving group departure occurs after the RDS for the reactions with the anionic nucleophiles. The large rho(X) value (1.7 +/- 0.1) obtained for the reactions of 1a-1 with the anionic nucleophiles supports the proposal that the reactions proceed through an addition intermediate with its formation being the RDS.

Varying resonance demands in substituent effects. Acetolysis of neophyl p-bromobenzenesulfonates

Abstract Rates of acetolysis of 2-aryl-2-methylpropyl p-bromobenzenesulfonates were determined for an extended series of substituents. The substituent effect can be described accurately in terms of our LArSR relationship (Yukawa-Tsuno Equation), giving an r value of 0.57. The correlation result can be reasonably accounted for on the basis of the accepted mechanism of this reaction, involving a rate-determining aryl-assisted transition state. The present study leads to the conclusion that this unique r value should be related to the resonance demand characteristic of the aryl-assisted ionization process of this reaction. The simple application of the Brown ϱσ + equation or its extended treatment and the interpretation based thereon are criticized.

Gas phase substituent effects in a highly electron deficient system. Intrinsic resonance demand of 1-aryl-1-(trifluoromethyl)ethyl cation

Abstract Gas phase stabilities of 1-aryl-1-(trifluoromethyl)ethyl cations were determined based on the proton transfer equilibrium. The LArSR analysis of the substituent effect gave a unique r value of 1.40 with a ϱ value of −14.0. This r value is identical with that for the corresponding solvolysis.

Resonance effect in solvolysis of 1-methylbenzyl chlorides

Abstract Substituent effects of p-MeO and p-MeS groups deactivated by additional m-substituents in cumyl and α-phenylethyl solvolyses were studied to provide evidence for the higher resonance demand in the α-phenylethyl system.

Substituent effects on the gas phase basicities of acetophenones

The gas phase basicities of m- and p-substituted acetophenones have been determined by the ion cyclotron resonance (ICR) equilibrium constant method. The application of the LArSR Eq. to these substituent effects provides a ϱ=12.2 and an r+=0.76 with excellent precision.

Substituent effects. XVI Acetolysis of 2-phenylethyl tosylates.

The acetolysis rates of 2-arylethyl tosylates were determined for a series of aryl substituents. The non-linear substituent effect was reasonably accounted for on the basis of two linear LArSR relationships; one for the aryl-assisted (FkΔ) and one for the unassisted (ks) processes, respectively. A precise dissection of the apparent substituent effect into individual effects for both processes was achieved in this manner. The substituent effect on the ks process can be described as a linear function of σ° with a small ρs of −0.19, and that on the FkΔ process in terms of the LArSR Eq., with ρΔ=−3.87 and an rΔ=0.631. The use of σ+ for the FkΔ process failed to give any reasonable dissection. The r value for this FkΔ process is essentially identical to that for the neophyl solvolysis. The unique r value of 0.6 is concluded to be characteristic of β-arylassisted ionization processes in general.

Substituent effect on the acetolysis of neophyl p-bromobenzenesulfonates

Abstract The substituent effect on the acetolysis of neophyl brosylates was analyzed successfully based on the analysis method of Yukawa-Tsuno. The basic concept of this method was strongly supported.