Bimolecular rate constants (kQ) were measured for the fluorescence quenching of a series of aromatic hydrocarbons by di-t-butylnitroxide (DTBN). In methylcyclohexane, measured values of kQ were close to the diffusion limit with only a 6.5-fold variation through the hydrocarbon series. A study of the viscosity dependence of the quenching reaction, in the Smoluchowski manner, suggests an interaction distance of 4–6 Å. A comparison is made of the efficiency of the DTBN and O2 fluorescence quenching reactions. Possible mechanisms are discussed.

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CN 74 ± 7 4.3 ± 0.4 X 107 a From T0bsd-1 = tl-1 + #csq [B]. 6 To be compared with tl = 27 s and Lsq = 1.25 X 108 M~' s'1, ref 3f. 1 Note that this is a corrected value for that previously reported by us as 5.5 qs. d To be compared with tl = 10 ± 1 qs and ksQ = 1.6 X 105 M~' s'1, ref 3g. e To be compared with ksQ = 3.25 X 105 M'1 s'1, ref 3g. / From benzene quenching data in Table II using the relationship tl'1 kq(Q) where (Q) 12 M.

S-( -) -N-(l-phenylethyl) diphenylvinylidene-x lo-, s-l, and in CD,CN, k (3.9 f 0.4) x lo-, s-l, with apparent 100% efficiency. f. amine (1) rearranges, apparently quantitatively, to S-( -)-2,2,3-triphenylbutyronitrile (2) in CCl,, k (2.9 0.3) x s-l, a t 60 "C s-l, and CD,CN, k (3.9 f 0-4) x