Selective dimerization by a radical chain reaction in γ-irradiated crystals of 1,3-bis(3-acetoxyprop-1-ynyl)-4-methoxy-6-methylbenzene

Abstract

A single dimer is formed by a radical chain reaction upon γ-irradiation of 1,3-bis(3-acetoxyprop-1-ynyl)-4-methoxy-6-methylbenzene (1) crystals, sealed in a glass ampoule under vacuum at room temperature. The dimerization is initiated by the addition of the prop-2-ynyl-type radical attached at the 1-position of the benzene ring to the β-carbon of the triple bond attached at the 3-position of the benzene ring. The resulting vinyl radical undergoes H-abstraction from the prop-2-ynyl methylene of the 3-acetoxyprop-1ynyl group attached at the 1-position resulting in a chain reaction. The dimerization proceeds after the γ-irradiation is stopped. The kinetic chain length of the dimerization may be more than 2 × 10 3 . Such an exclusive formation of a dimeric product by the γ-irradiation was observed neither for benzene solutions of 1 nor for crystals of other disubstituted bis(3-acetoxyprop-1-ynyl)benzenes. The crystal structure of 1 is responsible for the selective dimerization by the chain reaction. A mechanism for the chain reaction is proposed on the basis of the crystal structure.

Chemo- and Stereospecific Solid-State Thermal Dimerization of Sodium trans-2-Butenoate and γ-Ray-Induced Single-Crystal-to-Single-Crystal Dimerization of Hexaaquamagnesium trans-2-Butenoate Dihydrate: Both Give rel-(3S,4R)-1-Hexene-3,4-dicarboxylate but by Different Mechanisms. Stereospecific γ-Ray-Induced Trimerization of Sodium trans-2-Butenoate

“…The formation of both carbon–carbon bonds and hydrogen atom transfer is unequivocally topochemical, stereospecific, and not the result of a random process . , As indicated above, γ-ray-initiated solid-state polymerization reactions have been extensively studied. − On the other hand, there are very few examples of reactions of radical chain solid-state reactions that lead cleanly to monomeric, dimeric, or trimeric compounds. In addition to the formation of 3 , 5 , 7 , 9 , and 11 , the only examples we are aware of are the isomerizations of α-lactose monohydrate, , D-fructose, ,− and 2-deoxy-β-D- erythro -pentoypyranose , and the dimerization of a bis alkyne . In all of the highly stereospecific reactions we studied, the single crystals become amorphous as the reaction proceeds.…”

“…The crystal structure of triaquabis(trans-2-butenoato)magnesium (6) nose 36,41 and the dimerization of a bis alkyne. 42 In all of the highly stereospecific reactions we studied, the single crystals become amorphous as the reaction proceeds. While there are many examples of single-crystal-to-single-crystal transformations that arise from thermal and/or photochemical processes, 43,44 we are unaware of examples of γ-ray-induced transformations that proceed to monomeric, dimeric, or trimeric compounds with retention of single-crystal quality.…”

“…Thus, we hypothesized that, if (a) there were a minor component pair interleaved between two major component pairs and (b) it could be shown that this arrangement did not lead to unusually short contacts, the result would be a consistent geometrical mechanism that includes the 41 3.4 Å for D-fructose, 39 and 3.05−3.47 Å for a bis alkyne dimerization. 42,63 The only other hydrogen atoms that can be abstracted by the alkyl radical of dimer 19 are either sp 2 hydrogen atoms (bond strength 111 kcal/mol) or water hydrogen atoms (bond strength 117 kcal/mol) 64 that are too strongly bound to be abstracted by an alkyl radical. It is likely that the radical has a long lifetime in the crystal.…”

Crystal structures and solid-state reactivities of 1,4- and 1,2-bis(5-hydroxypenta-1,3-diynyl)benzenes and 1-(5-hydroxypenta-1,3-diynyl)-4-ethynylbenzene

“…We have previously reported on the reactions of γ-irradiated crystals of diethynylbenzene derivatives. [1][2][3] The crystal structures of the monomers were markedly affected by the nature of the substituents and their positions in the aromatic ring, leading to a variety of solid-state reactivities. Polymerization or dimerization occurred selectively depending on the crystal structures in contrast to the non-selective reactivities in solution.…”

“…The present study is concerned with the crystal structures and solid-state polymerization of bifunctional derivatives having diacetylene moieties. The structures and the melting points of the monomers, 1,4-bis(5-hydroxypenta-1,3-diynyl)benzene (1), 1,2-bis(5-hydroxypenta-1,3-diynyl)benzene (2) and 1-(5-hydroxypenta-1,3-diynyl)-4-ethynylbenzene (3), used in the present study, are shown in Fig. 1.…”