bluuebunny/crossref_metadata_2025_split huggingface dataset:
Chemistry of peroxyacyl nitrates. Part III. The oxidation of thioethers by peroxyhexanoyl nitrate
Authors: van Noort Paul C. M. , Vermeeren Hans P. W. , Louw Robert 
Published: September 2010

AbstractThe reaction of peroxyhexanoyl nitrate, 1a, a homologue of the atmospheric pollutant “PAN”, 1b, with some twenty thioethers, is described. At 0‐25°C, common thioethers such as Et2S or PhSMe are rapidly converted into sulfoxides in high yields in a variety of solvents, ranging from pentane and chloroform to acetic acid, methanol and aqueous acetonitrile. Rates are essentially solvent‐independent, although the reaction is subject to marked steric hindrance. Relative rates for five p‐substituted thioanisoles in MeOH at 22°C, leading to a Hammett ρ‐value of ‐1.7, show that the sulfur atoms display nucleophilic character. Electron‐attracting groups on α‐carbon, such as in PhSCCl3 and in MeSCH2OC(O)Ph, inhibit the formation of sulfoxide. Addition of EtSH lowers the yield of sulfoxide, producing instead EtSSEt and EtSNO. Oxidation of Me2S by 1a with the NO2 group labelled by 18O does not give rise to 18O‐enriched DMSO. Comparison of (CH3)2S with (CD3)2S revealed an inverse kinetic H/D isotope effect.The products obtained from 1a vary with solvent. In the presence of water or EtSH, hexanoic acid is formed, while methanol gives rise to methyl hexanoate, and in pentane/hexanoic acid, hexanoic anhydride is produced. In aprotic solvents, significant amounts of CO2 are formed.These observations can best be rationalized on the basis of an intermediate sulfurane R1R2S(ONO2)(OCOR), (I), produced from thioether R1SR2 and 1a, in the first step. The fate of I under various conditions is discussed.Finally, the features of the oxidation of thioethers by peroxyacylnitrate are compared with those of acyl peroxides and peroxy esters. It is suggested that in each case formation of a sulfurane may well be the first step.
Chemistry of crown ethers. Part XXII. Synthesis and complexing properties of monophospha‐crown ethers
Authors: van Zon A. , Torny G. J. , Frijns J. H. G. 
Published: September 2010

AbstractThe synthesis of phenyl‐ and tert‐butyl‐phosphadibenzo‐18‐crown‐6 and phenylphosphadibenzo‐21‐crown‐7 is described. The complexation of alkali metal cations and rhodium(I) by these macrocycles and their phosphine oxides has been studied by NMR methods. The phosphorus crown ethers are all capable of solubilizing lithium cations into chloroform. The phosphine oxide macrocycles also solubilize sodium cations. It is remarkable that tert‐butyl‐phosphadibenzo‐18‐crown‐6 complexes the sodium cation, whereas phenylphosphadibenzo‐18‐crown‐6, whose cavity is about the same size, does not. The formation of a bimetallic (Rh(I),Li+) complex of phenylphosphadibenzo‐21‐crown‐7 is discussed.
Temperature dependence of the primary kinetic isotope effect for hydride transfer mediated by a NAD(P)H‐model; discrimination between bent and linear transition states
Authors: van Gerresheim W. , Verhoeven J. W. 
Published: September 2010

AbstractTemperature dependence of the primary kinetic isotope effect for hydride transfer from 1‐benzyl‐1,4‐dihydronicotinamide (a NAD(P)H‐model) to the 10‐methyl‐9‐phenylacridinium ion conclusively shows the reaction to proceed through a linear transition state.
Photochemical ring contraction of 4‐heteroaryl‐substituted 1,4(or 3,4)‐dihydropyrimidines into imidazoles
Authors: van der Stoel R. E. , van der Plas H. C. , Jongejan H. 
Published: September 2010

AbstractPhotolysis of 4‐R‐1,4(or 3,4)‐dihydropyrimidines causes ring contraction into imidazoles, provided that the substituent R is capable of sufficiently stabilizing an anionic centre (R = 2‐thiazolyl, 2‐pyridyl, 4‐pyridyl). Chemical evidence is presented to show that the ring contraction of 6‐phenyl‐4‐(2‐pyridyl)1,4(or 3,4)‐dihydropyrimidine occurs via heterolytic fission of the C(1)‐C(6) bond of intermediate 1‐phenyl‐6‐(2‐pyridyl)‐2,4‐diazabicyclo[3.1.0]hex‐2(or 3)‐ene. The anion‐stabilizing effect of R is correlated with the acid strength (pKa) of R–CH3. A pKa value around 30 probably determines the border‐line between ring contraction into an imidazole and formation of an isomeric 5‐R‐1,2(or 2,3)‐dihydropyrimidine.
Activation and activity of ruthenium on silica hydrogenation catalysts
Authors: Koopman P. G. J. , Kieboom A. P. G. , van Bekkum H. 
Published: September 2010

AbstractActivation of RuCl3‐impregnated silica by hydrogen treatment at high temperature, up to 700°C, is superior to a procedure involving air calcination of the material prior to reduction. Upon direct reduction, sintering hardly occurs, whereas the Ru metal surface, as measured by hydrogen desorption, increases at higher activation temperature, due to the removal of chlorine impurities from the Ru surface. Activity measurements of the Ru catalysts for the liquid‐phase hydrogenation of benzene and cyclohexene reflect the favourable effect of the high‐temperature reduction of RuCl3/SiO2. Similar phenomena are observed for some PdRu/SiO2 catalysts.
Asymmetric synthesis of α,β‐epoxysulphonate esters (oxiranesulphonate esters)
Authors: Nkunya M. H. H. , Zwanenburg B. 
Published: September 2010

AbstractThe asymmetric phase‐transfer‐catalysed Darzens condensation of aldehydes and ketones with the chiral reagent L‐menthyl chloromethanesulphonate, using triethylbenzylammonium chloride (TEBA) as the phase‐transfer catalyst to give α,β‐epoxysulphonate esters (oxiranesulphonate esters) in 9–17% chiral induction, is described. The stereochemical course of the chiral induction is discussed.
Asymmetric induction in the addition of thioacetic S‐acid to α,β‐unsaturated esters
Authors: Gawroński Jacek K. , Gawrońska Krystyna , Kolbon Halina , Wynberg Hans 
Published: September 2010

Abstract2‐Methylpropenoates and cis‐ or trans‐butenedioates add thioacetic S‐acid under conditions of asymmetric catalysis by cinchona alkaloids to give optically active thioacetates. Structural factors influencing the stereochemical outcome of the reaction are discussed.
Photochemical reactions of some aromatic thiones with bis(methylthio)ethyne; (4 + 2)‐ versus (2 + 2)‐cycloaddition products. Spectroscopic evidence for the equilibrium thiete ⇄ α,β‐unsaturated dithioester
Authors: Brouwer A. C. , Bos H. J. T. 
Published: September 2010

AbstractIrradiation (λ > 525 nm) of the aromatic thiones 2 in the presence of bis(methylthio)ethyne 3 causes two cycloaddition reactions to occur between the photochemically excited thione 2 and the acetylene 3, as concluded from the isolated products. Compounds with structure 6 are believed to be products of a (4 + 2)‐cycloaddition reaction, whereas the formation of the isolated α,β‐unsaturated dithio esters 4 is rationalised on the basis of a (2 + 2)‐cycloaddition reaction. The preference for one reaction pathway over the other depends on the thione used and is discussed in terms of the structure of the thione 2. Spectroscopic observation of the equilibrium thiete 5 ⇌ α,β‐unsaturated dithio ester 4, in solution provides direct evidence for the (2 + 2)‐photocycloadducts, thietes 5.
Synthesis of α,β‐unsaturated sulfines from silylindenes and sulfur dioxide
Authors: Porskamp P. A. T. W. , van de Wijdeven A. M. , Zwanenburg B. 
Published: September 2010

AbstractThe synthesis of a variety of substituted indenethione S‐oxides (all α,β‐unsaturated sulfines) is described. Essentially these sulfines are prepared by the reaction of α‐silyl carbanions with an excess of sulfur dioxide (modified Peterson reaction). The requisite α‐silyl carbanions are generated by two different routes, i.e. by α‐deprotonation of trimethylsilyl‐substituted indenes and by nucleophilic δ‐addition of alkyllithium compounds to dienesilanes. In all cases, the sulfines prepared were converted into cycloadducts by reaction with 2,3‐dimethyl‐1,3‐butadiene.
Water‐ and hydroxide‐ion‐catalyzed hydrolysis of 1‐acyl‐1,2,4‐triazoles in mixed aqueous solvents. The effect of substrate hydrophobicity
Authors: Karzijn Willem , Engberts Jan. B. F. N. 
Published: September 2010

AbstractThe solvent dependence of the enthalpies and entropies of activation for the title reactions in water‐rich t‐BuOH‐H2O responds to the hydrophobicity of the substrate.
Synthesis of a teichoic acid fragment of Bacillus subtilis using a modified phosphotriester approach
Authors: van Boeckel C. A. A. , Visser G. M. , Hermans J. P. G. , van Boom J. H. 
Published: September 2010

AbstractThe synthesis of a teichoic acid fragment (i.e. compound 8e), containing three 3‐O–(β‐glucopyranosyl)‐sn‐glycerol residues connected via two phosphodiester linkages, is described. The assemblage of the teichoic acid fragment was effected using a modified phosphotriester approach based on the use of 1‐hydroxybenzotriazole‐activated phosphorylating agents (i.e. phosphorylating agents 5c and 6c). Three suitably protected building blocks were prepared: i.e., 2b, 3c and 4b. Special attention was paid to the preparation of the middle unit 3c which contains a stable phosphodiester anilidate to avoid intramolecular reaction of the free hydroxyl function on phosphorus. Compound 2b was condensed with derivative 3c to give fragment 7a. The aniline group could be removed from dimer 7a to give 7b, which was then condensed with monomer 4b to give the fully protected teichoic acid fragment 8a. Stepwise removal of the protecting group of 8a afforded the teichoic acid fragment 8e.
The decomposition of ethyl diazoacetate over zeolite NaCuX
Authors: Oudejans J. C. , Kaminska J. , van Bekkum H. 
Published: September 2010

AbstractThe decomposition of ethyl diazoacetate catalyzed by Cu(II)‐exchanged zeolite NaX, has been studied. Catalytic activity required at least 25% sodium exchange of the zeolite. From 25% exchange to higher exchange levels the decomposition rate increased linearly with the copper introduced into the zeolite. With cyclohexane as the solvent, the (ethoxycarbonyl)carbene formed was found to yield dimers, diethyl maleate and diethyl fumarate, and also compounds resulting from reaction with the solvent or with residual water present in the zeolite. Reduction of Cu(II) to Cu(I) increased the activity of the catalysts. The degree of hydration of the zeolite had a large effect on the activity of the catalyst and on the selectivity of the reaction. Complexation of the Cu(II) ions with NH3 or 1,2‐propanediamine reduced the activity of the zeolite drastically. Zeolite NaCuX showed no induction time in contrast to several copper salts tested.
Préparation d'un homologue de la PAP
Authors: Daunis J. , Elmahi M. , Ismaili H. , Jacquier R. , Calas B. , Parello J. 
Published: September 2010

AbstractA non‐statistical analogue of PAP, [poly(N‐acryloylpyrrolidine)], which can be used in peptide synthesis, is easily prepared by reaction of hexanediamine on chemically inert polyacrylic resin. It is shown that its functionalisation number depends upon the degree of cross‐linking in the chemically starting inert resin; swelling properties are slightly dependent upon the nature of the substituents present in the base acrylamide unit.
Chiral base catalysis in the reaction of thiols with a quinone epoxide
Authors: Pluim Henk , Wynberg Hans 
Published: September 2010

AbstractWhen p‐tert‐butylbenzenethiol is allowed to react with 2,3‐dimethyl‐1,4‐naphthoquinone 2,3‐epoxide in toluene in the presence of a cinchona alkaloid (e.g. cinchonidine) as catalyst, the ring‐opened β‐hydroxy sulfide is formed in optically active form (ee 65%). The reaction is a model for a biosynthetic step in the Vitamin K function.
Negative ion/molecule cycloaddition reactions of 2‐methylpropenal in the gas phase
Authors: Kleingeld J. C. , Nibbering N. M. M. 
Published: September 2010

AbstractThe gas‐phase negative‐ion chemistry of 2‐methylpropenal has been studied by Fourier transform ion cyclotron resonance mass spectrometry (FT‐ICR). Deuterium labelling has shown that the gas‐phase acidities of the methyl protons and the formyl proton are almost equal. The gas‐phase reactions of the 2‐formylallyl anion with several fluorinated substrates have been shown to proceed mainly via a cycloaddition mechanism.
Synthesis of [L‐m‐Tyr1]‐ and [D‐m‐Tyr1]‐leucine‐enkephalin via the REMA method
Authors: van den Braken‐Van Leersum A. M. , Maat L. 
Published: September 2010

AbstractThe synthesis by the all‐repetitive‐excess‐mixed‐anhydride (REMA) method is described for two analogues of leucine‐enkephalin, viz. [L‐m‐Tyr1]‐ and [D‐m‐Tyr1]‐leucine‐enkephalin, making use of enzymatically resolved (m‐hydroxyphenyl)alanine (m‐tyrosine).
Molecular aspects of methylated adenine in DNA. A quantum‐chemical study
Authors: van Lier Johan J. C. , Stroucken Jacques H. M. , Buck Henk M. 
Published: September 2010

AbstractOn the basis of modified neglect of differential overlap (MNDO) quantum‐chemical calculations on nucleoside systems, the effect of methylation of adenine on the anti‐syn equilibrium is described and an increased stabilization of the syn conformer, due to selective methylation, is calculated. A moderate anti‐syn activation energy has been found in the case of dm3A, dm6A and dm7A, whereas for dm8A a considerably higher anti‐syn energetic barrier exists. The results are combined with stereo model studies and related to biological data. With respect to restriction‐modification systems, special attention is given to the computed stereochemical freedom of the methyl group in dm6A, with a significant preference for the syn conformation in dm8A being found, leading to the suggestion that, out of the various methylated structures studied, only alternating d(m8A‐T) stretches are able to adopt a Z‐DNA duplex.
The photochemistry of 1‐, 3‐ and 4‐phenyl‐substituted 1,2‐dihydronaphthalenes
Authors: Lamberts J. J. M. , Laarhoven W. H. 
Published: September 2010

AbstractThe photochemical behaviour of 4‐phenyl‐1,2‐dihydronaphthalene (8) is similar to that of unsubstituted 1,2‐dihydronaphthalene (1). The main product is the 1‐phenylbenzobicyclo[3.1.0]hex‐2‐ene (10). 3‐Phenyl‐ and 1‐phenyl‐1,2‐dihydronaphthalenes (14 and 17) behave differently. 14 is photostable and 17 yields only the exo‐isomer of 4‐phenylbenzobicyclo[3.1.0]‐hex‐2‐ene, instead of a mixture of the endo‐ and exo‐isomer as would be expected. The different results are probably due to differences in the steric requirements of the first intermediate formed in the photoconversion.
Linear versus bent transition‐state structures in hydride‐transfer processes mediated by NAD(P)H model systems; a theoretical investigation
Authors: van der Kerk S. M. , van Gerresheim W. , Verhoeven J. W. 
Published: September 2010

AbstractThe reaction‐coordinate for degenerate hydride‐transfer between 1,4‐dihydro‐pyridine and the pyridinium‐ion was searched by MNDO calculations. A linear transition‐state (TS) structure is found to be strongly (> 16 kcal/mole) preferred over a bent TS. In the former, rotation about the C‐hydride‐C axis occurs unimpeded, thus creating a continuum of linear TS‐structures with ring to ring orientations varying between exo and endo.
Gas‐phase thermolysis of tert‐butyl hydroperoxide in a nitrogen atmosphere. The effect of added toluene
Authors: Mulder Peter , Louw Robert 
Published: September 2010

AbstractGas‐phase thermolysis of tert‐butyl hydroperoxide 1, ≤1% m in nitrogen (pyrex reactor, atm. pressure, 200‐300°C), gives methane and acetone as the main products. The homolytic mechanism involves O‐O bond dissociation (eqn. 1) and induced decomposition of 1 by hydroxyl and methyl radicals (eqn. 3).In the presence of a ≥50 fold excess of toluene, reaction (3) is suppressed, •OH and part of the •Me radicals abstracting hydrogen from toluene (eqn. 9).Values for k3b and k9b (abstraction by •Me) are derived and discussed. Arrhenius parameters for k1, log A/s−1 = 15.3, EA = 41.4 kcal/mol, are in agreement with the thermochemistry and with the results of the VLPP studies of Benson et al.
Stereochemistry of electrophilic addition reactions to 22E‐unsaturated sterols; a Barton rule revisited
Authors: Zeelen F. J. 
Published: September 2010

AbstractComparison of the X‐ray structures of seven 22E‐unsaturated sterols shows that these have the same conformation around the double bond. This minimum‐energy conformation has been used by Barton and others to explain the stereoselectivity observed in electrophilic addition reactions. The present study shows that this is only possible when the energy of the transition state of the addition reactions is low.
Pyrolysis of benzene and chlorobenzene in an atmosphere of hydrogen; formation of methane
Authors: Louw Robert , Dijks Johannes H. M. , Mulder Peter 
Published: September 2010

AbstractVapours of benzene and derivatives such as chlorobenzene are thermally unstable above ca. 500°C in both nitrogen and hydrogen atmospheres. Major products range from biaryls at lower temperatures to carbon black at temperatures above 1000°C. In hydrogen, dechlorination (ArCl → ArH) is a prominent reaction of (poly)chlorinated benzenes.In hydrogen, between 500‐1000°C, τ ∼ 5‐10 s, biaryl formation is accompanied by production of comparable amounts of methane. This reaction, for the major part, is shown not to be due to hydrogenolysis of carbonaceous deposits or of the small quantities of ethane/ethene which are also formed.A mechanistic rationale is presented based on isomerization of cyclohexadienyl radicals (formed in equilibrium with arene and •H), ultimately leading to •CH3 as the precursor of methane.
Synthesis of 6, 14‐ethenoisomorphinans and 6, 14‐ethenomorphinans based on Diels‐Alder adducts of 6‐demethoxythebaine and 6‐demethoxy‐β‐dihydrothebaine; pharmacology of the isomorphinans (Chemistry of Opium Alkaloids, Part XIX)
Authors: Crabbendam P. R. , Lie T. S. , Linders J. T. M. , Maat L. 
Published: September 2010

AbstractTwo different types of Diels‐Alder additions to morphinan‐6, 8‐dienes have been found. 6‐Demethoxythebaine (2) yielded ethyl 4, 5α‐epoxy‐3‐methoxy‐N‐methyl‐6, 14‐ethenoisomorphinan–7α‐carboxylate (3) with ethyl acrylate, in analogy to the reaction with thebaine. The ester 3 was converted into the alcohol 4, of which the 3‐methoxy ether was hydrolyzed to yield 5. Similarly, 2 gave the 7α‐acetyl‐6, 14‐ethenoisomorphinan 7 with methyl vinyl ketone. The latter compound was converted into 4 using methylmagnesium iodide. With propylmagnesium bromide, 7 afforded four compounds; two are new etorphine analogues (8 and 9), to which we were able to assign the absolute configuration; the other two are the Grignard reduction products 10 and 11.When the 4, 5α‐epoxy bridge of 2 is first opened, the Diels‐Alder reaction with methyl vinyl ketone proceeds from the other side of the diene system yielding the 7β‐acetyl‐6, 14‐ethenomorphinan 6, which belongs to a novel class of rigid morphinans.Preliminary pharmacological screening of 5, 8 and 9 showed these compounds to be potent agonists.
Enamine synthesis using the Horner‐Wittig reaction. Part 2. New acyl anion equivalents derived from (aminomethyl)diphenylphosphine oxides
Authors: Broekhof N. L. J. M. , van Elburg P. , Hoff D. J. , van der Gen A. 
Published: September 2010

AbstractUsing the Horner‐Wittig reagents (1‐morpholino‐alkyl)diphenylphosphine oxides (1), aromatic as well as aliphatic and α, β‐unsaturated aldehydes can be converted into the morpholino enamines of their respective homologous phenyl, ethyl and styryl ketones. These enamines can be easily converted into the corresponding ketones by mild, acid‐catalyzed hydrolysis. The usefulness of these phosphine oxides as acyl anion equivalents is further demonstrated by the synthesis of dihydrojasmone and of (Z)‐6‐henicosen‐ll‐one.
Facile synthesis of permethyl yttrocene hydride
Authors: den Haan Klaas H. , Teuben Jan H. 
Published: September 2010

AbstractA convenient three step synthesis of (Cp*2YH)n (Cp* = C5Me5) is described starting with YCl3·3thf, in which Cp*2YCl·thf and Cp*2YCH(SiMe3)2 are intermediates, which could be isolated and characterized. The hydride is active in the activation of sp2 and sp3 C‐H bonds as was demonstrated by the H‐D exchange between C6D6 and the methyl groups of CH2(SiMe3)2 at room temperature.
Oxidative and reductive ring opening of endo‐3,4‐O‐(4‐methoxybenzylidene) acetals of 1, 6‐anhydro‐β‐D‐galactopyranoses
Authors: Kloosterman M. , Slaghek T. , Hermans J. P. G. , van Boom J. H. 
Published: September 2010

AbstractCleavage of the endo‐3, 4‐O‐(4‐methoxybenzylidene) acetal rings of 1, 6‐anhydro‐β‐D‐galactopyranose derivatives with LiAlH4‐AlCl3, NaCNBH3‐HCl or NMe3‐AlCl3 gives predominantly axial 3‐O‐(4‐methoxybenzyl) ether derivatives. Oxidative opening of the same acetal functions with DDQ affords the corresponding 3‐O‐(4‐methoxybenzoyl) derivatives. The (4‐methoxybenzyl) group can be removed selectively with DDQ and survives acetolysis of the 1, 6‐anhydro bond.
α‐Imino sulfenates and α‐imino sulfoxides via electrophilic alkylation of amino sulfines (thioamide S‐oxides)
Authors: Lenz Bodo G. , Zwanenburg Binne 
Published: September 2010

AbstractTreatment of amino sulfines (thioamide S‐oxides) 1 with triethyloxonium tetrafluoroborate, followed by sodium carbonate, leads to α‐imino sulfenates 3. Reaction of 3 with primary and secondary amines gives α‐imino sulfenamides 5. Treatment of amino sulfines with sodium hydride, followed by an alkyl halide, leads to the formation of α‐imino sulfoxides 6, which are extremely sensitive towards hydrolysis. With ketenes, the imines 6 undergo a [2 + 2] cycloaddition reaction to give β‐lactams 8 in low yield.
Glucose‐isomerase‐catalyzed D‐glucose‐D‐fructose interconversion: Mechanism and reactive species
Authors: Makkee M. , Kieboom A. P. G. , van Bekkum H. 
Published: September 2010

AbstractThe isomerization of (1‐13C)‐D‐glucose to an equilibrium mixture of (1‐13C)‐D‐glucose and (1‐13C)‐D‐fructose by the enzyme glucose isomerase (E.C. 5.3.1.5) has been followed using 13C NMR spectroscopy. It is concluded that the α‐D‐glucopyranose and the α‐D‐fructofuranose form are the reactive species for the enzyme.
Steric control in the photochemical (E)‐(Z) isomerization of some (over)crowded α‐oxo oxime ethers
Authors: Buys Theo S. V. , Cerfontain Hans , Geenevasen Jan A. J. , Koppes Margareth J. C. M. , Stunnenberg Frank 
Published: September 2010

AbstractThe photoisomerization of a series of (highly) crowded α‐oxo oxime ethers (3–8) has been studied under conditions of direct irradiation (λ 300 and 350 nm) and of triplet photosensitization. The decay ratios k5/k6 for the two conditions are the same for a given compound, illustrating that the isomerization of the α‐oxo oxime ethers, upon direct irradiation, also proceeds from the (lowest) excited triplet state. The excited singlet and triplet state energies are reported, as well as ΔG0(E)‐ΔG0(Z) for 4 (‐ 8.2 ± 0.5) and 6 (7.7 ± 0.5 kJ·mol−1), determined by thermal equilibration with I2 at 353 K. The decay ratio k5/k6 is significantly smaller for 4 and 5 than for 3 and 6‐8 due to steric hindrance upon relaxation of the perpendicular ground state to the (E)‐isomer of 4 and 5.
The photochemical (4 + 2)‐cycloaddition of ortho‐quinones to triarylketenimines
Authors: Baaij J. P. B. , Kamphuis J. , Bos H. J. T. 
Published: September 2010

AbstractThe photochemical reaction of ortho‐quinones with triarylketenimines 4 yields quantitatively the dihydrodioxin derivatives 5 via a (4 + 2)‐cycloaddition. Kinetic studies on the photochemical reaction of phenanthrenequinone (PQ) with N‐(p‐tolyl)dipheriylketenimine show that the reaction proceeds irreversibly, probably via an exciplex of triplet PQ with the CC double bond and an allylic biradical: k2 = (1.18 ± 0.03)·109 1·mol−1·s−1 at 25°C in benzene (Scheme 2). Competition experiments between triplet PQ and N‐phenyl‐substituted triphenylketenimines (Ph2C = C = N − C6H4 − X) gave a good correlation between the relative rate constants and the normal Hammett σ‐constants ρ = −0.31, which indicates the absence of conjugation between the substituent X and the reaction centre at the C  C double bond and confirms the electrophilic character of triplet phenantrenequinone. From the Taft's DSP equation it follows that the blending constant λ = ρI/ρR = 1.02.