Diphenylacetylene (DPA) reacts instantly with sodium biphenylide (B• ™,Na+) in hexamethylphosphoramide (HMPA) and forms the radical ions DPA -. No further reduction takes place in HMPA even if B • -is in excess.

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2341be necessary to allow the quantity kc in the above equation to vary linearly with charge. Including this effect in the analysis of the trifluoromethyl compounds does not, however, change the essential conclusions. Assuming k, to be equal to 19 + 6.94qc gives a ring charge of -0.038 and a charge on the 1 carbon of -0.171, (15) J. A. Pople and M. Gordon, J. Am. Chem. SOC.. 89, 4253 (1967). Abstract: Isomerization of cis-stilbene in H M P A mediated by the free ions of stilbenides is governed by the mechanism. k l k 2 k-1 k -2Here the letters C and T refer to cis-and trans-stilbenes, respectively. The kinetic data demonstrate that K I = k l / k -l = 0.6 and k2 + k-2 = 1.5 X sec-I. Literature data indicate that k-1 is very large, at least IO8 M-I sec-I. Hence, the composition of the stilbenide radical ions is virtually maintained by equilibrium (1) and the spontaneous isomerization (2) is the slow rate-determining step, its relaxation time being -650 sec.( 2) To-Isomerization of stilbene induced by electron transfer was reported first by Hoijtink and van der Meij' who observed this reaction in the course of partial reduction of cisstilbene by alkali metal. The isomerization caused by the addition of lithium to THF solution of cis-stilbene was studied by Doran and Waack2 who monitored spectrophotometrically its progress. In both studies it was tacitly assumed that the stilbene radical anions mediate the isomerization, i.e., the reaction results from followed bywhere the symbols C and T refer to cis-and trans-stilbene, respectively.Detailed kinetic studies of cis-stilbene isomerization induced in THF by various salts of anthracenide anions, viz., Li+,A*-, Naf,A--, K+,A--, and Cs+,A. -, were reported recently by our g r o~p .~,~ Those reactions were found to be first order in cis-stilbene but otherwise more complex than originally anticipated. The C.-,Cat+ pairs present in THF are too stable to contribute significantly to the isomerization and the reaction proceeds through step 3, because the (3)dianions are more readily isomerized than the radical anions. The facile disproportionation of the latter4 maintains a reasonable concentration of the former and therefore a measurable rate of isomerization.The reported results imply that the cations bind together the adjacent phenyl groups of the cis form and thus hinder its isomerization. It became interesting, therefore, to investigate the isomerization involving free ions only. Since the C.' Tm-C2-, 2~a t ' -+ T~-, at+ ionic aggregates such as C.-,Cat+,C2-,2Cat+, etc., are likely to be fully dissociated in he~amethylphosphoramide~ (HMPA), we investigated the electron-transfer-induced isomerization of cis-stilbene in that solvent. Neither anthracenide nor pyrenide induces any observable reaction in HMPA, and we studied therefore the process initiated by a more powerful electron donor, viz., sodium biphenylide (Na+,B.-). This donor reacts instantly and quantitatively with the stilbenes yielding stilbenide radical ions. Hence, the investigated isomerization does not involve...

Carboxy-terminated oligomers of N,N-diethylacrylamide (DEAAm) with low polydispersity were synthesized by group-transfer polymerization. The oligomers were conjugated with the N terminus of epsilon-N-CBZ-protected poly(lysine) and s-CBZ-protected poly(L-cysteine). The resulting conjugates precipitated in a narrow region of lower critical solution temperatures (LCST) around 29 degrees C. The LCST of poly(lysine)-polyDEAAm-poly(lysine) conjugates was pH-independent and independent of the lengths of poly(lysine) segments. Water-soluble nonstoichiometric conjugate-DNA complexes precipitated above the conjugate's LCST. Covalent complexes of human albumin and poly(cysteine)-polyDEAAm-poly(cysteine) conjugates showed temperature-sensitive behaviour in aqueous solutions.