The reduction of diethyl fumarate (DEF) in tetra‐n‐butylammonium iodide (TBAI)‐dimethylformamide (DMF) solutions at a platinum electrode has been studied by cyclic voltammetry, double potential step chronoamperometry, and controlled potential coulometry. The chronoamperometric response for several possible mechanisms of electrohydrodimerization has been obtained by digital simulation techniques, and a method for distinguishing among the mechanisms suggested. Results of double potential step chronoamperometric experiments strongly support a mechanism where the electrochemically generated anion radicals undergo a second‐order dimerization reaction. Controlled potential electrolysis results give evidence for a bulk polymerization reaction in the absence of proton donor; protonation in the presence of hydroquinones; and good efficiency to the hydrodimer product in the presence of lithium perchlorate trihydrate.

corresponds to approximately 2 mg/dl in a 10-pl sample. Because this sample is diluted to more than 1 ml in the analysis, this detection limit is actually less than 1 ppm of the total analysis volume. The analysis time is generally less than 10 minutes.A unique feature of the method is the pH jump. This technique allows the enzyme to catalyze the reaction of glucose a t a favorable p H for a known length of time. The sudden change of p H to a level favorable to CL emission serves as a timing device for the enzyme reaction. Because of this, the method seems particularly amenable to automation; this aspect is currently under consideration. (Concurrent with this research, Bostick and Hercules (17) have independently developed an automated method for CL glucose analysis employing similar chemical techniques.) In addition, the extension of this technique to other oxidase enzyme systems is anticipated. The method would seem to be applicable to any substrate that yields hydrogen peroxide when it undergoes enzyme catalysis in neutral solution. ACKNOWLEDGMENT The authors thank Vicente Anido who supplied the analyzed human serum samples used in this work. The authors are grateful to D. M. Hercules for supplying a copy of his manuscript prior to publication. The efficiency of electrogenerated chemiluminescence (ECL) (decl) of several systems is reported using both potassium ferrioxalate actinometry and calibrated-photodiode measurements. Experimental methods and necessary corrections in &l-determinations are discussed and ECL in mixed solvent systems ( e.g., acetonitrile (ACN)-benzenetoluene) is described. The following deCl values were found: 9,lO-diphenylanthracene (DPA) (7.8mM), thianthrene (TH) ( 1 l . l m M ) (in mixed solvent): 20% peak efficiency, 5 % for several hours; DPA (7.7mM, in mixed solvent) 4%; DPA (2.20mM, in mixed solvent) 8 % ; rubrene (in benzonitrile) 1.9 YO. Good agreement between pulsed stationary electrode and rotating ring-disk electrode measurements and between actinometric and photodiode determinations was found. Electrogenerated chemiluminescence (ECL) involves the production of excited states, and ultimately light, by the ' Present address, D e p a r t m e n t of Chemistry, L o u s i a n a State '' Present address, Chemical Studies, Air Correction Div., P.O. Li A u t h o r t o w h o m correspondence a n d r e p r i n t requests should University, B a t o n Rouge, L a . 70803. B o x 1107. Darien. Conn. 06820.be sent.

Electrogenerated chemiluminescence (eel) resulting from the reaction of a,/3,7,5-tetraphenylporphin (TPP) anion radical with the cation radical of TPP, rubrene, or 10-methylphenothiazine in methylene chloride solutions is described. The eel emission is the same as that observed in TPP fluorescence and a mechanism is proposed

It is doubtful that additional force constant adjustments could be devised which would force the AQ and A¡ factors much below the values shown in Table III, without extending the models so far beyond what could be considered mechanistically reasonable as to make them meaningless. Our models, which were constructed not for mechanistic reasonableness, but specifically to produce low Arrhenius preexponential factors, did not result in values of Aq less than ~0.7 nor values of A{less than ~0.5. ConclusionsThere is probably no strictly defined lower limit to the value of the kinetic isotope effect Arrhenius preexponential factor, Aq, that can result, in the harmonic approximation, solely from force constant changes, at the isotopic position, between reactant and transition state. The present study indicates that, for sizable magnitude primary hydrogen kinetic isotope effects, increase in v4q with increasing temperature does not occur until temperatures as high as ~200°K (for the simple acid ionization model) to ~650°K (for the decarboxylation model) are attained. We are indebted to Professor Jacob Bigeleisen for pointing out to us a significant error in our original analysis of the temperature variation of Aq.(24) M.

Melts of scintillator compounds which are solid at room temperature, such as 2,5‐diphenyloxazole (PPO) and 2,5‐diphenyloxadiazole (PPD) containing several quaternary ammonium salts as supporting electrolytes, were examined as solvents for electrochemical and electrogenerated chemiluminescence (ECL) studies. Although the resistance of these solutions was high, cyclic voltammetry of 9,10‐diphenylanthracene and rubrene in PPO showed the production of stable radical anions and cations for both compounds, and the ECL emission was essentially the same as the fluorescence emission of these compounds in PPO. ECL of rubrene was also observed in molten phenanthrene, PPD, thianthrene, and p‐terphenyl, as well as in mixtures of PPO with 1‐ or 2‐methylnaphthalene.