Labelling styrene conversion

Fig. 12.7. Structures for the excited states Tj, T2, 5i, and S2 of styrene. Singlet-singlet conical intersections are labeled 1C (internal conversion). Singlet-triplet intersections are labeled ISC (intersystem crossing). Adapted from /. Am. Chem. Soc., 117, 6944 (1995), by permission of the American Chemical Society.

Figure 17. H P ID-nOe spectra of p-Hj enhanced (H)2Rh(PPh3)2(p-Cl)2Rh(PPh3) (styrene) (structure inset) at 295 K showing intramolecular hydride interchange and conversion to ethylbenzene during the 200 ms exchange time. The largest peaks in each trace correspond to the excitation or spin labelling point while the three smaller peaks are due to chemical exchange.

Pendent vinyl groups in styrene-divinylbenzene copolymers have been analysed by IR and Raman spectroscopy [73-84] and by wet chemical methods [83, 85] after extents of reaction varying from before gelation to after nearly complete conversion of monomers. Periysamy and Ford [86] report a new analytical approach to the problem. Copolymers of styrene with methane- C-labelled p-divinylbenzene were analysed by liquid-state and solid-state cross-polarisation magic angle spinning (CP-MAS) i C-NMR methods. 

The radical chain mechanism was considered because these reactions have induction periods and because styrene added to the reaction mixture is polymerized242. However, in the reaction of 2-picoline 1-oxide with acetic anhydride, whilst the formation of carbon dioxide and methane demonstrates the presence of free radicals, these are irrelevant to the main reaction, the addition of radical scavengers being without effect on the yield of 2-pyridylmethyl acetate. Further, conversion of 2-picoline 1-oxide by butyric anhydride into 2-pyridylmethyl butyrate is not influenced by the presence of acetate ions. These facts point to the intra-molecular production of radical or ion pairs in a solvent cage as the essential characteristic of the reaction243a. Similar experiments in which i 0-labelled acetic anhydride was used and the effect of solvents studied, point to the same conclusion and favour the formation of a radical pair in a solvent cage for the reaction both... 

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