Remarkable Substituent Effect Research Articles

Para-substituent effect upon the oxygenation reaction of the benzyl radical in solution

The oxygenation rate constants ( k O 2 ) of the ground-state para-substituted benzyl radicals ( p-X-benzyls) were obtained by Stern-Volmer plots for the decay of the transient D n ←D 0 absorption in the presence of various concentrations of dissolved molecular oxygen. A remarkable substituent effect, a sharp drop in the k O 2 value in the order of p-chlorobenzyl, p-phenylbenzyl, p-bromobenzyl, p-nitrobenzyl and p-cyanobenzyl, was confirmed in contrast to almost the same k O 2 values of (3.0±0.4) × 10 9 M −1 s −1 for p-X-benzyls (X = H, CH 3, OCH 3 and F).

Remarkable substituent effects on the micellar enantioselective hydrolysis of amino acid esters

The remarkable substituent effects were observed for the enantioselective hydrolysis of the long-chained and nitro-substituted phenyl esters; With respect to the enantioselectivity, p-isomers (k ψ L/k ψ D = 40.2) > o-isomers (20.1) > m-isomers (10.8) and with respect to the rate-enhancement, o-isomers > p-isomers ⪢ m-isomers, respectively.

Thermal behaviour of aryl γ-haloprcpargyl ethers

A systematic study of the behaviour of aryl γ-halopropargyl ethers under thermal condition was undertaken. Aryl γ-bromopropargyl ethers 2 underwent unique transformation in N,N-diethylanillne (215°C, 6 h) giving rise to a mixture of products 3 , 4 and 5 , whereas, under similar conditions aryl γ-chloropropargyl ethers ulbar|8, afforded 4-chlorochromenes, 9. A remarkable substituent and solvent effect has been observed in the thermolysis of these aryl γ-bromo and γ-chloropropargyl ethers, rendering this transformation as a method for the synthesis of a number of substit uted 4-bromochromenes 3 , 4-chlorochromenes 9 and chroman-4-ones 7 . In contrast, solution thermolysis of aryl γ-iodopropargyl ether 11 afforded aryl propargyl ether 1 as the major product.

Pyrrole and pyridine derivatives via 1,7-cyclization of butenynyl nitrones the product-determining influence of substituents on the deactivation pathway of the oxaza-cycloallene intermediates

A remarkable substituent effect is described for the thermal transformation of three butenynyl nitrones into pyrrole and pyridine derivatives.The results are best explained by assuming oxaza-cycloallenes, cyclopropenes, and, most importantly, carbonyl carbenes as intermediates.

Remarkable substituent effects found in the base‐catalyzed reaction of 5‐methyl‐2‐(4′‐substituted‐phenyl)‐2,4‐dihydro‐3H‐pyrazol‐3‐ones

AbstractRemarkable substituent effects found in the base‐catalyzed reaction of 5‐methyl‐4‐(1‐methylethylidene)‐2‐(4′‐substituted‐phenyl)‐2,4‐dihydro‐3H‐pyrazol‐3‐ones (2) with acetone at reflux are described.