Conformational barriers in triplet 1- and 2-naphthylcarbene. 2. Absolute rate of decay of arylcarbenes by electron spin resonance spectroscopy

Abstract

k , .a s-' 2.8 \ k:; M-' s-' k , , M-' s-' 4a-thiol addition k,, s-' k f , S-' 0.5 4.5 2.6 3.8 H, 0 solvent oxidations ( M -l s -l ) of I-3.0 95%EtOH 0 r " H o r ' s W W k , , s-'4a-peroxide dissociation a The k , values have been extrapolated to zero buffer concentration. Table V reveals that with a particular solvent, the values of AAG* (=AGlci -AGIN1) are similar for the reactions investigated (save the acid-catalyzed process associated with kl of pseudobase formation). This observation supports a greater electrophilicity of the 4a-position of the N' flavins when compared to the C1 flavins and a greater polarization of the peroxide moiety of the N1-4a-F1Et00H as compared to C1-4a-F1Et00H. Inspection of Table V also shows that the dissociation rate constants (for RS-, HO-, and HOO-) from the 4a-position of the N1 flavin are larger than those seen with the C' flavin. The ground states of C1-fix+Et and &+Et differ in free energy content by the same amount as the ground states of the products C1-4a-FlEtX and 4a-FlEtX. Lowering of the free-energy content of the transition state for addition of X must also lower the ground state for dissociation of X and by the same value of AAG*. Particularly noteworthy from Table V is the similarity of the AAG* for the N-and S-oxidation reactions in DMF to the AAG* for dissociation of peroxide from the C' and N' flavin hydroperoxides in that same solvent. Evidently the difference in polarization about the C,,-OOH bond in 4a-FlEt00H relative to CI-4a-FlEtOOH is reflected in the difference in polarization about the C b W H bond and in facilitation of the N-and S-oxidation reactions. Inspection ofFrom the present study, it is concluded that 1-carba-1-deaza FAD should, if recognized by the enzyme, serve as a cofactor for the hepatic flavoprotein microsomal oxidase in the N-oxidation of amines and the S-oxidation of sulfides.Acknowledgment. This work was supported by grants from the National Institutes of Health and the National Science Foundation. We should like to acknowledge the experimental con-

The Naphthylcarbene Potential Energy Hypersurface

“…These conclusions are readily confirmed by the small triplet rotational barrier between 2st and 2at (theory, 3.5 kcal mol -1 ; experiment, >4.4 kcal mol -1 ; singlet barrier (theory), 29.6 kcal mol -1 ). The MO's depicting the most important orbital interactions of the naphthyl fragment and the exo -methylene clarify the situation.…”

“…There are ten structures to be discussed (energies and geometries are summarized in Tables −3): the syn and anti conformers of singlet and triplet 1-naphthylcarbene ( 1ss , 1as , 1st , and 1at , respectively), as well as the analogous isomers for 2- naphthylcarbene ( 2ss , 2as , 2st , and 2at , respectively), and the transition structures [ TS1s (singlet) and TS1t (triplet)] for the interconversion of the syn and anti configurations of 2-naphthylcarbene ( 2st → TS1 → 2at ). The latter isomerization has been studied experimentally for the triplet state; the results provide calibration with theory.…”

Photochemistry of 1‐pyrenyldiazomethane*

“…The pyrenyldiazomethane was stored at low temperature. The product was identical to that produced by Creary (1986) and Senthilnathan and Platz (1981) who characterized the material in greater detail.…”

“…The synthesis of this compound was originally described by Senthilnathan and Platz (1981), using a slightly different procedure. The procedure used here is as follows: 1.183 g of pyrenecarboxaldehyde was partially dissolved in 10 mL of methanol and a solution of 0.95 g ofp-toluensulfonylhydrazide in methanol was added.…”

Konformációváltozások kinetikájának modellezése elsőrendű reakcióhálózatokkal

“…ionerősség, pH, szolvatáció) szerepe nem elhanyagolható, a szá-mításos kémiai procedúrák mellett kísérleti technikákat (mikrohullámú- [209,210], Raman- [211], IR- [212], UV- [213], NMR- [214,215], illetve ESR-spektroszkópia [216]) is célszerű igénybe venni, amelyek közül -Zwier egy összefoglaló tanulmányára [148] alapozva -az infravörös és az ultraibolya-látható technikákkal foglalkozunk részletesebben.…”