Comparisons of Photo-Fries Rearrangements of 4-Dodecylphenyl Phenylacetate and Two Structurally Related Esters in Hexane and Polyethylene Cages. How Important Are Anchoring Chains?†

Abstract

Photo-Fries rearrangements of 4-dodecylphenyl phenylacetate have been investigated in polyethylene films with 0-71% crystallinity and in hexane over a range of temperatures. The results are compared to those reported previously from phenyl phenylacetate and 1-naphthyl tetradecanoate to assess the influence of a long alkyl chain on the in-cage motions of the intermediate singlet radical pairs. It is demonstrated that the reactivity and selectivity of intimate singlet radical pairs can be tuned by judicious placement of long-chain substituents and selection of a specific polyethylene type as the reaction matrix.

Cage Effect under Photolysis in Polymer Matrices

“…One approach is based on product analysis of photodissociation of organic compounds in polymers. It was successfully used by Weiss, Chesta, and their collaborators [8][9][10][11][12][13]. Norrish type I cleavage of 1-(4-alkylphenyl)-3-phenyl-2-propanone (ACOB) was used as a probe of polymer matrices:…”

“…Photochemistry experiments were done in PE not only with ACOB but also with naphthyl esters and ethers undergoing photo-Fries and photo-Claisen reactions [12,13]. The two latter reactions proceed via singlet RPs [12,13].…”

“…Photochemistry experiments were done in PE not only with ACOB but also with naphthyl esters and ethers undergoing photo-Fries and photo-Claisen reactions [12,13]. The two latter reactions proceed via singlet RPs [12,13]. It was concluded that polymer free volume V f was the dominant factor controlling the diffusion of the benzyl and other radicals, and, therefore, the kinetics of cage recombination and cage escape [10].…”

Dynamics of Radical Pair Processes in Bulk Polymers

“…In hexane solutions, two photoproducts, 2-myristoyl-1-naphthol and 4-myristoyl-1-naphthol are obtained in a 1.3/1 ratio 68b ; only one photoproduct, 2-myristoyl-1-naphthol (2-AN), is obtained in unstretched LDPE and HDPE. 68b, 70 The irradiations of 1-NA and 1-NM have also been investigated above (at 323K) and below (273K) the Tg of two poly(vinyl acetate) films (PVAC-83 and PVAC-140; average molecular weight 83K and 140K, respectively). 71 The results in Table 13 representative.…”

Reaction mechanisms : Part (i) Radical and radical ion reactions

“…103 In a very interesting application of radical chemistry to materials research, Weiss et al used the photo-Fries rearrangement of phenyl phenylacetate (Scheme 29) to probe the size, shape, and wall stiffness of cavities formed in polyethylene films. 104 Because a radical pair is produced, these environmental factors impact the rates, stereo-and regiochemistry of in-cage combinations, and the rate of cage escape, which in turn is reflected in the nature of the products formed.…”