An Interpretation of Meta Orientation in the Alkylation of Toluene. The Relative Reactivity and Isomer Distribution in the Chloromethylation and Mercuration of Benzene and Toluene<sup>1,2</sup>

Brown, Herbert C.; Nelson, K. LeRoi

doi:10.1021/ja01120a053

Cited by 83 publications

(26 citation statements)

References 15 publications

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“…Similarly, the relative reactivity of two similar aromatic compounds, e. g . toluene and benzene, towards different electrophiles gives a measure of the extent of interaction in the transition state as assumed in the rule of Brown and NeZson [28]. Since the selectivities[**' given in this way vary from ca.…”

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confidence: 99%

The Perturbation Treatment of Chemical Reactivity

Hudson

1973

Angew. Chem. Int. Ed. Engl.

159

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geometrical properties of the methane derivatives. A more detailed analysis has to be based upon this fact.The polynomial (2 a) appears to describe the T,-contribution in an acceptable approximation, at least for those derivatives having ligands from Table 6, and to predict the correct sign for derivatives whose optical rotations are not too small. It should be profitable on the one hand to continue the test in the form described and on the other to use the results of a quantum-mechanical theory of the phenomenon, which have been completely disregarded here, to correlate the Td-component and contributions due to deviations from the Td-situation with physical or geometrical details. It should ultimately be possible to obtain information from the optical activity about preferred conformations in methane derivatives or about changes in the geometric arrangement as a result of association, solvent effects, etc. We regard the test carried out here as a first successful step on the way to this goal.We thank B. Weimann (MPZ fur Kohlenforschung, Miilheim) for the calculation of optimum values of the parameters and for the program required for this purpose. We thank the Deutsche Forschungsgemeinschaft for financial support of B. R. Received: June 6,1972 [A 922c IE] German version: Angew. Chem. 85,21 (1973) [l] E. Ruch and A. Schiinhofer, Theor. Chim. Acta 10,91 (1968) [2] E. Ruch, W Runge, and G. Kresze, Angew. Chem. 85, 10 (1973); Angew. Chem. internat. Edit. 12,20 (1973).[3] E. Rucfi and A. Schiinhofer, Theor. Chim. Acta 19,225 (1970 Chem. 594,76 (1955).[9] P. Karrer, P. Portmann, and M . Suter, Helv. Chim. Acta 31, 1619Acta 31, (1948.[lo] D. Pitre and E. B. Grabitz, Chimia 23, 399 (1969).[ll] G. Smolinsky and B. I . Feuer, J. Amer. Chem. SOC. 86,3085 (1964).[12] L. G. Thomi, Chem. Ber. 36, 582 (1903).[13] A. Kjaer and S. E. Hansen, Acta Chem. Scand. 11,898 (1957).[14] C . Djerassi, K . Undheim, R . C. Sheppard, W C . Terry, and B. Sjoberg, Acta Chem. Scand. 15,903 (1961).[IS] N . N . Kalinina, A . M . Kritsyn, A. M . Likhosherstov, T K Protopopova, and A. P. Skoldinov, Zh. Obshch. Khim. 33,3471 (1963 The perturbation method of treating chemical reactions is discussed in a simple manner, by invoking the general hypothesis that the initial perturbation determines the course of a reaction. This approach is used to develop a general theory, as an alternative to the transition state theory. Such apparently diverse concepts as the symmetry rules for cyclic processes, and hard and soft acids and bases can be derived by this treatment, which is applied to radical reactions and aliphatic and aromatic substitution. IntroductionThe quantitative treatment of reactivity remains one of the most difficult and yet intriguing problems of chemistry, of particular importance in the field of reaction mechanisms. Chemical reactivity is usually discussed in terms of the transition state theory"], but this method has severe limitations ['] in that neither the activation energy nor the activation entropy can be calculated to wit...

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confidence: 99%

The Perturbation Treatment of Chemical Reactivity

Hudson

1973

Angew. Chem. Int. Ed. Engl.

159

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“…rate 38.5 [5] These reactions also reveal high selectivity between the exo and endo isomers of norbornyl (8, 13) (Eqs. 6 [9] Clearly, this last reaction is not a satisfactory one to explore structural effects in the norbornyl system.…”

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“…In other words, a reaction which exhibits a high degree of selectivity between toluene and benzene shows high selectivity between the meta and the ortho + para positions of toluene. One which exhibits low selectivity between toluene and benzene shows low selectivity between the meta and the ortho + para positions of toluene (9).…”

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The Selectivity Principle and the Question of the Bridged Structure of the 2-Norborynyl Cation

Brown

Peters²

1974

Proc. Natl. Acad. Sci. U.S.A.

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Low exo/endo rate ratios in the solvolysis of certain norbornyl derivatives have been attributed to the involvement of classical (unbridged) 2-norbornyl cations. Consequently, the high exo/endo rate ratio in the parent system, 2-norbornyl arenesulfonates, has been interpreted as involving rate enhancement in the exo isomer arising from a-participation. It is pointed out that this treatment involves neglect of the Selectivity Principle. Taking the relative reactivity of cyclopentyl to cyclohexyl as a representative test system, it is pointed out that those reactions which reveal low exo/endo rate ratios in norbornyl also reveal low cyclopentyl/cyclohexyl rate ratios. It is proposed that the low exo/endo rate ratios in norbornyl, observed in the above reactions, arise from the low selectivities of the test reactions. Consequently, the results cannot be utilized to support the argument that low exo/endo rate ratios reflect the absence of a-participation and high exo/endo rate ratios reflect the presence of ¢-participation.Since 1962 (1) there has been active discussion as to whether the high exo/endo rate ratio (280) in the acetolysis of norbornyl toluenesulfonates (tosylates, OTs) involves steric factors (2) or a-participation (3). The respective interpretations may be summarized as follows. and the interpretation that these low ratios are characteristic of classical (unbridged) 2-norbornyl cations (4).For example, the exchange of methoxyl groups in norcamphor dimethyl ketal in methanol-d4 at 31.80 (5) In this case the low ratio is attributed to the delocalization of charge from the carbonium ion center through allylic resonance, thereby preventing a-participation. Similarly, the solvolysis in 70% aqueous acetone at 100°o f the 3-spirocyclopropylnorbornyl 3,5-dinitrobenzoates (ODNB) (7) yields an exo/endo rate ratio of 2.8 (eq. 3).The available evidence has recently been reviewed and subjected to detailed analysis by G. D. Sargent (4). The author concludes that the high exo/endo rate ratio in tertiary 2-norbornyl systems is the result of steric factors. On the other hand, he reaches the conclusion that the high exo/endo rate ratio in the secondary 2-norbornyl systems is the result of electronic factors, namely a-participation in the exo and its absence in the endo.It is rare in science for such similar phenomena to have such different physical bases, as proposed.Careful examination of the arguments reveal that the author's conclusion that a-participation is responsible for the high exo/endo rate ratio in secondary 2-norbornyl derivatives rests largely upon low exo/endo rate ratios which have been observed in certain reactions of norbornyl derivatives (5-7) + ODNB ODNB [3] Here it is the cyclopropylcarbinyl cationic system which facilitates the charge delocalization postulated to inhibit ubridging.These low exo/endo rate ratios are considered to be characteristic of unbridged norbornyl systems. It is therefore argued that the much higher exo/endo rate ratio, 280 (8), observed in the acetolysis of 2-norborn...

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“…this ratio was 0.5. This may be compared with the decrease by one nitro group of the reactivity of benzene towards nitration of 1 the order of lo6 (7), and with the fact that whereas the isopropyl cation is very reactive and non-discriminating in its attack upon toluene (8), nitrobenzene may be used as a I solvent in Friedel-Crafts alkylations. The kinetics of the thermal decomposition of I (I; X = CO) in aqueous acid solution have established that the rate-determining step I is the SN1 decomposition of the diazonium salt and that the substituent R has a small, predictable effect upon this step (6).…”

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Aromatic Substitution: Part Ix. On the Mechanism of the Pschorr Cyclization

Abramovitch¹,

Tertzakian²

1965

Can. J. Chem.

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The decomposition of the diazoniuni salt from 3-(0-ami1iobenzoy1)pyridine has been studied under various conditions. A competitive-type cyclization of an equi~nolar ~iiixture of the diazonium salts of 2-aminobenzophenone and 2-arnino-3'-nitrobenzophenone has also been carried out. The results are interpreted in ternis of a radical process in the copper-catalyzed reactions. I t is suggested t h a t the uncatalyzed thermal decompositions in aqueous acid s o l u t i o~~ give rise to a diradical cation interlnediate in equilibriu~n with the aryl cation.

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An Interpretation of Meta Orientation in the Alkylation of Toluene. The Relative Reactivity and Isomer Distribution in the Chloromethylation and Mercuration of Benzene and Toluene^1,2

Cited by 83 publications

References 15 publications

The Perturbation Treatment of Chemical Reactivity

The Perturbation Treatment of Chemical Reactivity

The Selectivity Principle and the Question of the Bridged Structure of the 2-Norborynyl Cation

Aromatic Substitution: Part Ix. On the Mechanism of the Pschorr Cyclization

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An Interpretation of Meta Orientation in the Alkylation of Toluene. The Relative Reactivity and Isomer Distribution in the Chloromethylation and Mercuration of Benzene and Toluene1,2

Cited by 83 publications

References 15 publications

The Perturbation Treatment of Chemical Reactivity

The Perturbation Treatment of Chemical Reactivity

The Selectivity Principle and the Question of the Bridged Structure of the 2-Norborynyl Cation

Aromatic Substitution: Part Ix. On the Mechanism of the Pschorr Cyclization

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An Interpretation of Meta Orientation in the Alkylation of Toluene. The Relative Reactivity and Isomer Distribution in the Chloromethylation and Mercuration of Benzene and Toluene^1,2