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A novel class of photochemically active amphiphiles has been synthesized containing a ketone moiety as a biradical or radical pair precursor on the hydrophobic tail of sodium sulfate surfactants. Alteration of the molecular structure of each ketone-containing surfactant allows for the systematic and predictable manipulation of the micellar size and shape, both of which are important in determining the coupling between the unpaired electrons confined within the micelle and the intraradical dynamics. The structure of the resulting aggregates has been analyzed by small-angle neutron scattering (SANS). The results show that the amphiphiles form ellipsoidal micelles with aggregation numbers between 30 and 150 that depend on the balance between monomer dimensions and steric effects caused by the atomic spatial arrangement within the hydrophobic tail of the different surfactants.

X-band time-resolved electron paramagnetic resonance (TREPR) spectra of 1,16- and 1,21- acylalkyl biradicals, obtained in toluene solution at low temperatures (187−253 K), are reported. The spectra show a strong temperature dependence in their patterns of chemically induced electron spin polarization. The spin-correlated radical pair (SCRP) mechanism dominates at high temperatures, while the radical pair mechanism (RPM) is the main pattern at lower temperatures. It is postulated that the SCRP spectrum is suppressed at the lower temperature due to molecular motion on a time scale which modulates the exchange interaction (J) between the unpaired electrons. Simultaneously the RPM is enhanced by this motion. Average values of J calculated from end-to-end distance distributions for the C21 biradical show that in the absence of this dynamic effect, an intense SCRP spectrum would be present at the lower temperature. The results demonstrate that the interpretation of average J couplings may be difficult in temperature regions where these motional effects dominate the appearance of the spectrum.

The olefin metathesis reaction is of great synthetic utility in polymer chemistry. The recent development of ring-opening (ROMP) and acyclic diene (ADMET) metathesis polymerization reactions has opened new avenues for the synthesis of novel polymeric materials. Recently the authors used ADMET to synthesize several photochemically active poly(keto olefins) using the catalyst Mo(CHCMe[sub 2]Ph)(NAr)(OCMe(CF[sub 3])[sub 2])[sub 2] (Ar = 2,6-diisopropylphenyl) (1) developed by Schrock and co-workers in 1990. In the course of that work, they discovered that neat samples of highly substituted dienes will cyclize quantitatively via metathesis to give difunctional five- and seven-membered rings instead of the expected linear polymer. Examples of substituted diene cyclizations by metathesis even in the presence of a solvent are rare. Their systematic exploitation in organic synthesis has therefore been limited to two recent studies by Fu and Grubbs, who cyclized several substituted diene ethers, amines, and amides to unsaturated oxygen and nitrogen heterocycles. Cyclization of unsubstituted dienes in various solvents has been reported, but complete conversion occurred in only a few cases. Formation of cyclic alkene oligomers from back-biting during the ROMP reaction is also known. The reactions reported here are unusual in that they are intermolecular between catalyst and substrate, yet can givemore » 100% yield of product solely from the monomer in the absence of solvent. 13 refs.« less