Active 4 years, 1 month ago. Viewed 12k times. Improve this question. Add a comment. Active Oldest Votes. I invite you to draw the mechanisms by yourself: A reaction that involves carbon atoms 1 and 4 or 5 and 8.
Possible, by mechanism. There are five double bonds remaining in conjugation, and you count one six-membered ring in the state of "a benzene ring" the very left one. In the very right six-membered ring, there is only a single double bond, too. Alternatively, a Diels—Alder reaction with carbon atoms 9 and It is so much favourable to the former, that this is the reaction observed. Pure anthracene is usually found as a colourless crystal solid. It does not readily dissolve in water, but will dissolve in organic carbon-containing solvents.
Is anthracene a carcinogen? Anthracene, also called paranaphthalene or green oil, a solid polycyclic aromatic hydrocarbon PAH consisting of three benzene rings derived from coal-tar, is the simplest tricyclic aromatic hydrocarbon. Carcinogenicity bioassays with anthracene generally gave negative results. Why is phenanthrene more stable than anthracene? When two electrons are removed, i. How do you prepare anthracene?
Preparation of anthracene Pieces of porous pumice stone of a size that will conveniently pass into a combustion tube are added to a paste prepared from g of good zinc dust and 30 ml of alcohol. The mixture is stirred to incorporate the pumice and paste. Is c14h10 soluble in water? Phenanthrene is nearly insoluble in water but is soluble in most low polarity organic solvents such as toluene, carbon tetrachloride, ether, chloroform, acetic acid and benzene. Gratifyingly, we could successfully achieve regioselective functionalization of the terminal rings of 9,unsubstituted anthracenes by placing sufficiently strong electron-donating substituents at the 1- or 1,5-positions which exert their effects by imposing largest orbital coefficients in the HOMO at the 1,4-positions of the anthracene moiety making the transformations kinetically favored with highly asynchronous transition states leading to the corresponding 1,4-cycloadducts and substitution products.
Synthetic valorization of the 1,4-cycloadducts has also been demonstrated. Herein, we describe our results in detail.
Next, we turned our attention to evaluating alkyne dienophiles such as dimethylacetylene dicarboxylate DMAD, D which are also known for being exclusively 9,selective for unsubstituted anthracene 11 1a , Fig. The 1,4-cycloadduct 3bD was isolated and unambiguously characterized by spectroscopic and single-crystal X-ray analysis Fig.
The structure of the 1,4-cycloadduct 3cD was again confirmed by single-crystal X-ray analysis Fig. Diels-Alder reactions between 1,5-disubstituted anthracenes and alkynes D-F. Accordingly, we synthesized the monosubstituted pyrrolidino anthracene derivative 1e for details see Supplementary Methods. In contrast, methyl phenylpropiolate F did not undergo any cycloaddition reaction with 1e.
The structures of the 1,4-cycloadducts 3b—eD were unambiguously assigned by nuclear magnetic resonance NMR spectroscopy and were confirmed by single-crystal X-ray diffraction analysis Fig.
Analogous to the cycloaddition reactions, electrophilic aromatic substitution of anthracenes generally takes place in the central B ring as a consequence of maximizing the aromatic stabilization energies in the transition state 15 , 16 , Electron-donating substitution effect on the reactivities of anthracenes was also evident when electrophilic substitution reactions were compared between unsubstituted anthracene 1a and pyrrolidine anthracene 1e with different electrophiles such as N -arylmaleimides, MTAD, and bromine.
The practical benefits of our developed methodology could be gleaned from the results of the synthetic exploration of the 1,4-cycloadducts particularly focusing on the exploitation of the isolated, unsubstituted olefinic moiety at the 11,positions in various types of reactions. Next, a formal 1,3-dipolar cycloaddition reaction was performed on the same olefin functionality employing N -hydroxybenzimidoyl chloride 12 as the precursor for the corresponding N -phenyl nitrile oxide Accordingly, when 3eD was reacted with 2.
Considering the easy functionalizability of the ester groups in 14 , this route could provide an expedient access to varied 2,3-disubstituted anthracene derivatives which might otherwise be difficult to obtain despite of being useful in a number of transformations 20 , We propose that the reaction proceeds via the initial formation of a cyclic bromonium ion intermediate 16 at the 11,positions of 3eD and then with the anchimeric assistance from the pyrrolidine nitrogen lone pair, a [1,2]-sigmatropic shift takes place to form the iminium intermediate 17 that upon hydrolysis furnishes the skeletally rearranged product 15 in good yield 22 , The structure of 15 was unambiguously determined by spectroscopic data and single-crystal X-ray analysis see Supplementary X-Ray Crystallographic Studies and Supplementary Data 6.
The fundamental question arises, which governs the 9, vs. The two dienophiles B and D were picked as they show a stark contrast in their position-selectivity in the reactions with the dienes 1a - e. Whereas D followed a smooth trend from 9, to 1,4-selectivity with the variation of the electronics of the dienes, B apparently was insensitive to this and showed expected 9,selectivity only.
A judgment about the minimum energy pathways MEP, concerted vs. The calculations have been run with the Gaussian For further details and citations see Supplementary Computational Studies. The calculated activation barriers reproduce the experimentally observed trend of 9, to 1,4-cycloaddition selectivity as a function of the electron donor substituent ED at the diene Table 1. Therefore, this LOT was used for a more detailed analysis. To determine the extent of concertedness, transition state TS structures were analyzed with respect to the extent of the bond reorganization Fig.
Color coding: yellow squares C9-C10 product, blue circles C1-C4 product. Interestingly, the cycloaddition of D even with the parent anthracene 1a the TS structures of the 9,addition, as well as the 1,4-addition, are asynchronous, with the 1,4-addition slightly more so Fig.
This is contrary to the TS structures with maleic anhydride B Fig. Based on the analysis of the RMS gradient along the calculated IRC a stepwise mechanism was identified to be in operation for the 1,4-additions of D with 1d and B with 1b - 1d. With the help of this energy and force related differentiation of concerted vs. A definition of step-wise vs.
Therefore, we opted for an approach based on the RMS gradient analysis. Based on the MEP-analysis the comparison of the Gibbs free activation barriers of the 9, vs. In case of the addition reaction with D the 1,4 addition is consistently facilitated by increasingly electron-donating substituents, whereas the 9,addition barrier is significantly less sensitive to changes in the diene electronics see Supplementary Tables 2 — 4 and in addition, shows no consistent correlation.
On the contrary, the 1,4-addition product is thermodynamically significantly less stable than the 9,addition product and moreover, the driving force for the 1,4-product formation decreases with increasing strength of the electron donor ED; see Fig.
Clearly, there is no linear free energy relationship in operation. A Variation of the anthracene exemplified for 1a and 1d in presence of D leads to changes in the regioselectivity that are driven by kinetic parameters. B Based on the FMO analysis this regioselectivity is intrinsic to the anthracene biggest orbital coefficients. On the contrary, changing the dieneophile from D to B this intrinsic and kinetic preference of the 1,4-product is overwritten by its unfavorable thermodynamics.
Energies were calculated using the harmonic oscillator approach and include zero-point energy corrections for further details see Supplementary Computational Studies.
Kinetic control of the product formation may be rationalized by a maximal orbital overlap in the rate-determining step. Therefore, we focused our analysis on the understanding of how the amino substituents change the electronic FMO and nuclear structure of the transition states TSs and the dienes in favor of the 1,4-addition process.
This analysis is based on the frontier molecular orbitals FMOs , and the natural bond orbital NBO analysis partial charges. Although the 1,4-addition pathway is shifting from a concerted to a step-wise bond reorganization in the series 1a to 1e the FMO analysis of the anthracenes turned out to correctly predict the position selectivity in the reactions with D. This article is cited by 9 publications. Brittni A. Qualizza , Jacob W.
Experimental survey of the kinetics of acene Diels-Alder reactions. Journal of Physical Organic Chemistry , 28 10 , Chemistry - A European Journal , 21 5 , Angewandte Chemie , 41 , Angewandte Chemie International Edition , 51 41 , Atherton , S.
Diels—Alder reactions of anthracene, 9-substituted anthracenes and 9,disubstituted anthracenes.
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