Electrophilic reactivity in anti-Mills-Nixon systems

Eckert‐Maksić, Mirjana; Glasovac, Zoran; Maksić, Zvonimir B.; Zrinski, Irena

doi:10.1016/0166-1280(96)04515-0

Cited by 25 publications

(20 citation statements)

References 40 publications

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“…40 Moreover, it is interesting to mention that in systems exhibiting the reversed MN effect, the orientational ability of small ring(s) in controlling the electrophilic reactivity is diametrically opposed to that in MN systems. 41,42 Hence, it follows that the electrophilic reactivity of fused molecules is well understood. A point of utmost importance is the fact that the MN effect on the electrophilic reactivity is a result of a combined action of angular strain and cationic resonance.…”

Section: Discussionmentioning

confidence: 99%

The Mills–Nixon effect and chemical reactivity—methyl cation affinity of some cycloalkabenzenes

Eckert‐Maksić

Glasovac

Coumbassa

et al. 2001

J. Chem. Soc., Perkin Trans. 2

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The problem of the methyl cation attack on carbon atoms belonging to the benzene moiety fused to small rings is explored by the ab initio models at the MP2 level of sophistication. It is shown that the β-position is more reactive than the α-site in kinetically controlled reactions, which is in accordance with the original Mills-Nixon postulate. On the other hand, it appears that in thermodynamically controlled electrophilic substitution reactions the α-site should be slightly preferred for three-, four-and five-membered annelated rings. The differences between the methyl cation affinities MCA β and MCA α are analyzed and resolved into angular strain and the cationic resonance contribution. The latter involves the hyperconjugation/conjugation and relaxation effects. It turns out that the angular strain contribution is inversely proportional to the size of the annelated ring, whereas the opposite is the case for the cationic resonance interaction. Their interplay determines the selectivity and its extent in the electrophilic substitution reactions. The same analysis is applicable to other electrophilic groups.

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Section: Discussionmentioning

confidence: 99%

The Mills–Nixon effect and chemical reactivity—methyl cation affinity of some cycloalkabenzenes

Eckert‐Maksić

Glasovac

Coumbassa

et al. 2001

J. Chem. Soc., Perkin Trans. 2

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“…There were, however, some facts that were not explained by the above-mentioned studies, such as why some of the molecules (for example, 3 ,12a 4 , and 5 ) that should exhibit positive Δ R show, in fact, negative Δ R . Extreme examples of systems that show distortion which is apparently inconsistent with SIBL were studied by Maksic et al and by Siegel et al, who have calculated the structures of bora- and aza-substituted cyclopropabenzenes. The concept of these studies was to use heteroatoms in order to introduce different numbers of π electrons, leaving all the rest of the conditions almost unchanged.…”

Section: Introductionmentioning

confidence: 99%

Strain-Induced Bond Localization. The Heteroatom Case

Stanger

1998

J. Am. Chem. Soc.

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Strain-induced bond localization (SIBL) has been a debated issue for almost 70 years. In the past decade there have been some developments that showed that strain can indeed localize aromatic bonds. However, some compounds that should have exhibited positive ΔR (Mills−Nixon distortion) showed instead negative ΔR (anti-Mills−Nixon distortion), apparently more coherent with π effects (aromaticity−antiaromaticity arguments). Using ab initio methods, the structure of cyclopropabenzenes, cyclobutabenzenes, and benzocyclobutadienes, where the three- and four-membered rings consist of carbon, nitrogen, or boron, were calculated at the B3LYP/6-31G* level of theory. Analyses of these structures show that SIBL and not aromatic factors are responsible for the localization observed in the aromatic moieties, both with positive and negative ΔR.

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“…Other possible C 6 D 5 B reaction products considered, phenylborylene ([D 5 ]-2) and the didehydroborepine isomer ([D 5 ]-3), were found to be much higher in energy than 1 and thus could be excluded as reaction products. While 1 has been repeatedly studied with respect to the Mills-Nixon effect, [17][18][19] 2 was sought experimentally in 1970 by Fox et al 20 The 1-naphthyl analogue (also called 1-naphthylboryne) of phenylborylene 2 was reported in 1977 to result from irradiation (λ > 350 nm) of tri-1-naphthylboron in solution, 21 but this claim was refuted 7 years later. 22 The only theoretical investigation of 2 has been reported by Uddin et al, 23 who studied its bonding properties in transition metal compounds, while 3 has never been studied before to the best of our knowledge.…”

Section: Introductionmentioning

confidence: 99%

Reaction of Benzene and Boron Atom: Mechanism of Formation of Benzoborirene and Hydrogen Atom

Bettinger

Kaiser

2004

J. Phys. Chem. A

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The reaction of C 6 D 6 + B( 2 P) is investigated by crossed molecular beam experiments at a collision energy of 5.5 kcal mol -1 and by electronic structure computations. The latter were performed employing hybrid Hartree-Fock/density functional theory (B3LYP), coupled cluster theory with single, double, and a perturbative estimate of triple excitations [CCSD(T)], complete active space self consistent field (CASSCF), and multiconfiguration quasi-degenerate perturbation theory to second order (MC-QDPT2) in conjunction with 6-31G*, 6-311+G**, and cc-pVTZ basis sets. Final energies were obtained at the CCSD(T)/cc-pVTZ//B3LYP/ 6-311+G** + ZPVE level of theory. Two possible addition channels to the benzene π system were characterized. One involves a weakly bound benzene-boron π complex and proceeds over a barrier, which lies below the energy of separated reactants, to an η 1 C 6 H 6-B σ complex (4). The second channel is the symmetric attack (η 2 ) to a π bond of benzene. This addition mode following the 2 A′′ potential energy surface involves a valley ridge inflection (VRI) point and therefore results in 4. This VRI point also makes the formation of the 7-boranorbornadiene-7-yl radical (6, 2 A′) via nonadiabatic transition from 2 A′′ to 2 A′ unlikely. The primary addition products 4 (and 6) can rearrange over barriers below the energy of separated reactants to finally reach the phenylboryl radical (10, 2 A′). This is the most stable C 6 H 6 B species identified. Cleavage of an o-CH bond goes along with closure of a C-B bond and yields benzoborirene (1, 1 A 1 ) and hydrogen atom (-19.2 kcal mol -1 ; -16.7 kcal mol -1 for the [D 6 ]-benzene system). Abstraction of hydrogen by boron to produce phenyl radical ( 2 A 1 ) and borylene ( 1 Σ + ) is endoergic by +30.4 kcal mol -1 (C 6 D 5 + BD, +31.6 kcal mol -1 ) and is therefore not viable under our experimental conditions. The features of this C 6 D 6 B potential energy surface identified computationallysno entrance barrier with respect to separated reactants, exoergicity of -16.7 kcal mol -1 , transition state energy and structure in the exit channel (6.5 kcal mol -1 with respect to 1 + D)sare in agreement with crossed-beam data (exoergicity -14.8 ( 1.2 kcal mol -1 ; exit channel barrier 2.4-4.8 kcal mol -1 ). Phenylborylene 2 and didehydroborepine 3 are alternative C 6 H 5 B species, but these are higher in energy than 1 by 32 and 43 kcal mol -1 and are therefore not formed in the crossed-beam experiment.

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Electrophilic reactivity in anti-Mills-Nixon systems

Cited by 25 publications

References 40 publications

The Mills–Nixon effect and chemical reactivity—methyl cation affinity of some cycloalkabenzenes

The Mills–Nixon effect and chemical reactivity—methyl cation affinity of some cycloalkabenzenes

Strain-Induced Bond Localization. The Heteroatom Case

Reaction of Benzene and Boron Atom: Mechanism of Formation of Benzoborirene and Hydrogen Atom

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