Crystal Structure and the Radiation-Induced Free-Radical Chain Reaction of 2-Deoxy-β-D-erythro-pentopyranose in the Solid State

Abstract

<jats:title>Abstract</jats:title><jats:p> The crystal structure of 2-deoxy-β-D-enrythro-pentopyranose (1) was reexamined by X-ray crystallographic studies. In crystalline 1, a radiation-induced chain reaction occurs with the only product being, 2,5-dideoxy-D-enrythro-pentonic acid (4). In the chain propagating step leading to 4, an H atom is transferred over a distance of ≤ 3.3 Å as taken from interatomic distances in the unperturbed crystal. The crystal structure clearly indicates the direction by which the chain reaction proceeds through the crystal. The strong temperature dependence of G(4) is discussed in terms of temperature effects on chain initiation, propagation and termination rates.</jats:p>

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 4.521 Å distance between the carbon radical and the methyl hydrogen atom in propagation step 2 of the major–major reaction (and the analogous distances of 4.090 and 4.034 Å for the major–minor reaction) are much longer than those that we and others have observed in γ-ray initiated radical chain reactions as taken from monomer–monomer distances which are 3.13 Å for 4 , 3.32 Å for 6 , 3.31 or 3.55 Å for 8 , 3.10 or 3.30 Å for 10 , 3.09–3.30 Å for 2-deoxy-β-D-erythro-pentopyranose, 3.4 Å for D-fructose, and 3.05–3.47 Å for a bis alkyne dimerization. , 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) 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.…”

“…Apart from our work with trans- 2-butenoates − and early work with carbohydrates, − there are no systematic studies of the chemo-, regio-, and stereospecific syntheses of small molecules using ionizing radiation. We hope that our studies will stimulate the search for new classes of these reactions.…”

“…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.…”

“…We thought that a group IIA metal with a shorter radius might also form a trans-2-butenoate salt with the correct orientation to form a cyclodimer, hopefully the diastereomeric trans,trans-nepetate 7. 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.…”

“…2.2:1, the majorcomponent mechanistic reaction pathway (Figure 8) must be considered, but we cannot use the same process to propose a sensible mechanism for the minor component: the singlecrystal-to-single-crystal radical chain process cannot proceed under those circumstances. 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.…”