bluuebunny/crossref_metadata_2025_split huggingface dataset:
Crime behaviours and distance travelled in homicides and rapes
Authors: Santtila Pekka , Laukkanen Manne , Zappalà Angelo 
Published: July 2007

AbstractWe explored (1) distances between home and offence in homicides and rapes; (2) whether these distances differed from each other; and (3) whether offence features were associated with distances. The sample consisted of solved homicides (N = 40) and rapes (N = 37) from Finland with co‐ordinates for offence and offender home locations and information on crime features. Empirical models of incident density as a function of distance were estimated using CrimeStat III (Levine, 2004). Most of the distances were short displaying distance decay. Homicide median distance was 0.85km (Inter Quartile Range (IQR) = 0.13–7.69km) and rape median distance 2.44km (IQR = 0.83–6.96km) from perpetrators' home location. These distances differed significantly (Mann‐Whitney U = 543.0, p < 0.045). It was possible to identify crime features that were correlated with distances in both offence types. Spatial Behaviour Indices combining crime feature information correlated rs = 0.77 with distance in homicides and rs = 0.72 in rapes. Identifying theoretical constructs for understanding links between different crime features instead of looking at them in isolation is important. Copyright © 2007 John Wiley & Sons, Ltd.
Neuartige Diterpenoide aus den Ritterlingen Tricholoma aurantium und T. fracticum (Agaricales)
Authors: Knops Liliana , Nieger Martin , Steffan Bert , Steglich Wolfgang 
Published: July 2007

Novel Diterpenoids from the Toadstools Tricholoma aurantium and T. fracticum (Agaricales)Herrn Professor Dr. Heinz G. Floss zum 60. Geburtstag gewidmet.
Two novel diterpenoids trichaurantin (1) and its 6‐O‐acetyl derivative 2 have been isolated from Tricholoma species. Their structures were established by spectroscopic methods and an X‐ray crystal analysis, 1 and 2 appear to be biosynthetically related to the neodolabellane and dolastane group of diterpenes and can be designated as 2,3‐seconeodolastane derivatives.
Strukturmodifizierte Isokalafungine und Isonanaomycine
Authors: Hoffmann Bernd , Lackner Helmut 
Published: July 2007

Structurally Modified Isokalafungins and IsonanaomycinsThe total synthesis of structural analogues of the unnatural, C‐6‐hydroxylated isokalafungins and isonanaomycins is described. The new compounds show improved antibiotic activity and support theories for a mechanism of action which base on the formation of reactive quinone methides. Calculations of the molecular structures show that the chromophore of the most active 9‐methyl derivatives 28 and 32 is bended off along its 5‐CO‐10‐CO axis. This corresponds to an unusual shifting of characteristic 13C‐NMR signals. Different experiments for the introduction of X‐CH2‐ or sugar residues into 1 (e.g. isolactoquinomycins) demonstrate the limits of the general synthetic pathway. Finally a short overview on significant structure/activity relationships in the (iso)nanaomycin D field is given.
Chiralitätsgesteuerte Strukturvarianten von Bis(sulfoximin)/Metall‐Komplexen
Authors: Zehnder Margareta , Bolm Carsten , Schaffner Silvia , Kaufmann Daniel , Müller Jürgen 
Published: July 2007

Chirality‐Monitored Structural Variants of Bis(sulfoximine)/Metal ComplexesThe coordination geometries of sulfoximine/metal complexes differ substantially depending on the metal and on whether optically active or racemic sulfoximines are used for their preparation. Two copper and two zinc complexes have been characterized by X‐ray diffraction analysis.
Reactivity of cyclopentenyl anion analogous heterocycles: 1,5‐electrocyclization of 2‐oxa‐, 2‐thia‐, 2‐aza‐ and 2‐phosphabicyclo[3.2.0]hept‐3‐ene. A sigmatropic [1,3] carbon shift
Authors: Klärner Frank‐Gerrit , Yaslak Salih , Drewes Rolf , Gesenberg Christoph , Peter Michael 
Published: July 2007

AbstractCarbonyl ylide‐like intermediates are involved in the 1,5‐electrocyclization of the bicyclo[3.2.0]heptenes 3a–c. The activation barriers analyzed by the time‐ and temperature‐dependence of the exo ⇌ endo isomerization of specifically deuterated derivatives or of the racemization of optically active derivatives turned out to be higher by Δ ΔG≠ ≥ 11 kcal/mol than those determined for the corresponding bicyclo [3.1.0]hexenes 1a–c. This result can be considered as an evidence for the electrocyclic nature of these ring openings due to the diminished Walsh character of cyclobutane bonds compared to cyclopropane bonds. A stereochemical analysis of the fragmentation of 2‐oxabicyclo[3.2.0]heptene 3a to furan and ethene leads to the conclusion that a sigmatropic [1.3] carbon shift proceeding with inversion of the migarting carbon followed by stereospecific retro‐Diels‐Alder reaction is the major pathway for this reaction similar to the rearrangement and fragmentation of the corresponding carbocycle 3e.
Enantioselective synthesis of α‐branched α‐amino acids with bulky substituents
Authors: Studer Armido , Seebach Dieter 
Published: July 2007

AbstractEnantiopure 5,5‐disubstituted t‐butyl 2‐t‐butyl‐3‐methyl‐4‐oxoimidazolidine‐1‐carboxylates readily available by diastereoselective double alkylation of the parent compound (Boc‐BMI) can be converted to α‐branched α‐amino acids with two bulky substituents (PhCH2/Et, PhCH2/i‐Pr, PhCH2/CH2C6H11) in four simple steps: hydrolysis to the amino acid amides, N‐benzoylation, cleavage of the amino acid amide group, and debenzoylation (Scheme 3, products 6–10, overall yields >50%). This procedure constitutes an extension of the scope of amino acid synthesis from (R)‐ and (S)‐Boc‐BMI.
Preparation of α‐chiral crotylsilanes by retro‐[1,4]‐brook rearrangements. A stereochemical study
Authors: Behrens Karin , Kneisel Boris O. , Noltemeyer Mathias , Brückner Reinhard 
Published: July 2007

AbstractTreatment of alcohols cis‐22, cis‐23, and trans‐23 with PPh3/ Ph2S2 provided three mixtures of isomers of α, γ‐disubstituted allyl phenyl sulfides. They consisted of diastereomers and ‐except starting from trans‐23–of regioisomers. Each mixture was lithiated reductively by lithium naphthalenide at −78°C in THF. α, γ‐Disubstituted allyllithium compounds resulted which underwent retro‐[1,4]‐Brook rearrangements within 30–90 min. A high degree of stereocontrol by 1,3‐asymmetric induction was observed in the rearrangement starting from a 5:1 mixture of the tBuPh2Si‐containing sulfide regioisomers cis‐25 and iso‐25 (each regioisomer consisting of more than one diastereomer): The α‐chiral crotylsilane anti, trans‐26 was formed as a racemic mixture with ds = 93:7:0:0 in preference to isomer syn,trans‐26 which possesses the opposite configuration at the silicon‐bearing stereocenter and in preference to the corresponding cis isomers (Scheme 5). The rearrangements of the two other sulfide mixtures were much less stereoselective and exhibited ds = 49:44:4:3 starting from the two tBuPh2Si‐containing diastereomers of the isomeric sulfide trans‐25 (Scheme 5) and ds = 59:41 starting from the 3.5:1 mixture of the MePh2Si‐containing sulfide regioisomers cis‐24 and iso‐24 (each regioisomer consisting of more than one diastereomer; Scheme 9). The stereostructures of the rearrangement products were determined by chemical correlations, NMR analogies, and a crystal structure analysis of 27. It was proven that the stereochemical outcome of the retro‐[1,4]‐Brook rearrangements of the MePh2Si‐containing 3.5:1 mixture of sulfides cis‐24/iso‐24 is kinetically rather than thermodynamically controlled (Scheme 10). Mechanistic aspects are discussed in Schemes 11–13.
Modellsysteme zur artifiziellen Photosynthese – Synthese und Elektronentransferstudien neuartiger Sensibilisator‐Relais‐Einheiten
Authors: Seiler Martin , Dürr Heinz 
Published: July 2007

Modell Systems for an Artificial Photosynthesis – Synthesis and Electron Transfer Studies of Novel Sensitizer‐Relais AssembliesSyntheses and determination of electron transfer rates between sensitizers and electron acceptors for a novel class of bis(4,4′‐dimethyl‐2,2′‐bipyridine)[4,4′‐bis(alkoxymethyl)‐2,2′‐bipyridin]ruthenium(II) complexes 6–8 are described. We report on the formation of supramolecular complexes between the dialkoxybenzene‐tethered bisheteroleptic Ru(II)‐bipyridine complexes 5, 8 and 1,1′‐dimethyl‐4,4′‐bypiridinium (MV2+) and cyclo‐[bis(1,1′‐p‐xylylene‐4,4′‐bipyridinium)] (BXV4+), respectively. Evidence for the formation of supramolecular sensitizer‐relais assemblies is taken from the viologen radical and hydrogen production rates in sacrificial model systems for artificial photosynthesis.
Thermal rearrangements of 1,2‐dialkoxybenzenes by flash vacuum pyrolysis
Authors: Gröschl Dieter , Meier Herbert 
Published: July 2007

AbstractFlash vacuum pyrolysis of 1,2‐dialkoxybenzenes 1a‐c leads to the liberation of alkanes from the interacting side chains. A rearrangement of the skeleton yields the o‐hydroxy carbonyl compounds 2 and 4. The generation of phenol 3 can be rationalized by a decarbonylation. The latter reaction is the sole process which can be observed for the bicyclic starting compound 9.
Nickel‐catalyzed cross‐coupling reactions of bicyclo[1.1.0]butylmagnesium bromide and bicyclo[1.1.0]butyllithium derivatives with alkynyl chlorides and bromides
Authors: Stephen A. , Hashmi K. , Vollmer Antje , Szeimies Günter 
Published: July 2007

AbstractSeveral alkynylbicyclo[1.1.0]butanes are prepared by coupling of bicyclo[1.1.0]butylmagnesium bromide with alkynyl chlorides. Severe side reactions, which take place with alkynyl bromides, are not observed. Bridgehead‐lithiated bicyclo[1.1.0]butanes are also effective components in these reactions. The coupling occurs by nickel catalysis as shown by control experiments, an uncatalyzed nucleophilic substitution at the acetylenic carbon atom not being a major reaction path. Alkyl‐ and aryllithium compounds could also be coupled with alkynyl chloride 13c, but in the case of alkynyllithium reagents side reactions decreased the synthetic value of this alkynylic coupling procedure.
Substituted metallotriazolehemiporphyrazines: Synthesis and characterization by FAB‐MS
Authors: Fernández‐Lázaro Fernando , Schäfer Wolfram , Torres Tomás 
Published: July 2007

AbstractNovel triazolehemiporphyrazines 3a, 4a, and 5a, substituted on the isoindole units and soluble in organic solvents, have been synthesized by condensation of 3,5‐diamino‐1,2,4‐triazole with the corresponding 1,3‐diiminoisoindoline. First‐row transition‐metal complexes 3b–e, 4b–e, and 5b–e have also been prepared by reaction of the free ligands 3a, 4a, and 5a with the appropriate metal(II) salt. A FAB mass spectrometric study of this kind of metallomacrocycles is reported. Triazolehemiporphyrazines 3–5 show electrical conductivities in the range of 10−12‐10−9 Scm−1.
Kinetische Untersuchungen zur Ligandenhydrierung in Katalysatorvorstufen für die asymmetrische Reduktion prochiraler Olefine
Authors: Heller Detlef , Kortus Karin , Selke Rüdiger 
Published: July 2007

Kinetic Investigations of the Hydrogenation of Ligands in Catalyst Precursors for Asymmetric Reduction of Prochiral OlefinesHerrn Professor Kurt Madeja zum 70. Geburtstag gewidmet.
The comparison of chiral rhodium(I) complex catalysts of the type [Rh(L)PP*]A (L = cyclic diolefin; PP* = chiral bis(phosphane) and A = anion like BF) regarding their hydrogenating activity against prochiral substrates is hampered by the induction period in the hydrogen consumption which can be attributed to the formation of the catalytically active species from the diolefin precatalyst. The competing hydrogenation of diolefin [e.g. cis,cis‐cycloocta‐1,5‐diene (COD), norborna‐2,5‐diene (NBD)] and prochiral substrate may cause a maximum of the hydrogenation rate, which is characteristic for different catalyst/substrate/solvent systems. Michaelis‐Menten rate constants for the hydrogenation of COD and NBD were determined for different chiral catalysts by stoichiometric and catalytic hydrogenations. The rate constants differ for one selected diolefin up to a factor of 40. The hydrogenation of NBD is generally 5–8 times faster than the COD hydrogenation. In the special case of precatalysts based on he‐xopyranoside bis(phosphinites) the rate constants for the NBD hydrogenation in comparison with those for COD are higher up to a factor of 48. In some cases the hydrogenation of the mono‐ene is faster than that of the diolefin (e.g. COD, NBD). The high hydrogenation rate reported in the literature for some precatalysts in the asymmetric hydrogenation of prochiral olefins is caused in part by the relatively fast diolefin hydrogenation which facilitates the complete formation of the catalyst. The influence of substrate, solvent, and some experimental conditions on the induction period will be discussed.
Spirostanol glycoside from the tuber of Ophiopogon japonicus
Authors: Branke Jürgen Thomas , Haslinger Ernst 
Published: July 2007

AbstractA steroidal saponin isolated from the tuber of Ophiopogon japonicus. The structure of the saponin was elucidated by several one‐ and two‐dimensional NMR experiments to be (25S)‐1‐O‐β‐D‐fucopyranosyl‐3‐O‐α‐L‐rhamnopyranosylrus‐cogenin.
The effect of pressure on the trimerization and Diels‐Alder reaction of cyanoacetylene. Synthesis and reactivity of 2,3,5‐tricyanobicyclo[2.2.0]hexa‐2,5‐diene („tricyano Dewar benzene”︁)
Authors: Breitkopf Volker , Hopf Henning , Klärner Frank‐Gerrit , Witulski Bernhard , Zimny Bernd 
Published: July 2007

AbstractThe trimerization of cyanoacetylene (1a) and the Diels‐Alder reaction of 1a with 1,3‐cyclohexadiene (2) show a powerful pressure‐induced acceleration which allows the reaction temperature to be reduced from 160°C at 1 bar to 40°C at 12 kbar or from 100deg;C at 1 bar to room temperature at 7 kbar. At high pressure thermally unstable intermediates like the tricyano Dewar benzene 12 generated in the trimerization of 1a or the primary adduct 3a formed in the Diels‐Alder reaction of 1a with 2 were isolated.
Addition and cyclization reactions in the thermal conversion of hydrocarbons with enyne structure, II. Analysis of radicals and carbenes from ethynylbenzene
Authors: Guthier Klaus , Hebgen Peter , Homann Klaus‐Heinrich , Hofmann Jörg , Zimmermann Gerhard 
Published: July 2007

AbstractThe pyrolysis of ethynylbenzene (1) in helium was studied in a tubular flow reactor at 10.7 mbar/1030°C and reaction times ranging from 5 to 30 ms. Reactive intermediates such as radicals and carbenes were scavenged with dimethyl disulfide (DMDS), Qualitative and quantitative analysis of the scavenging products and of the stable pyrolysis products were carried out by GC‐MS analysis. – The radicals phenyl (2a), o‐, m‐, and p‐ethynylphenyl (1c, d, e), 2‐ and 1‐phenyl‐vinyl (1a, b) 1‐ and 2‐naphthyl (3a, b), methyl, hydrogen atoms, and radicals resulting from the addition of phenyl and ethynylphenyl radicals to the triple bond of ethynylbenzene were detected. Carbenes, such as phenylvinylidene, occur only in small traces and obviously play no role in the overall pyrolysis. Concentration profiles of the radicals and of some important pyrolysis products are presented and discussed. Based on the detected radicals, a reaction scheme for the pyrolysis of ethynylbenzene is proposed. Results of pyrolyses of mixtures of ethynylbenzene and ethyne show that naphthalene (3), acenaphthylene (12), and other compounds are produced by a sequence of ethyne addition and cyclization reactions.
First total synthesis of the 2,7‐naphthyridine alkaloid neozeylanicine and unexpected formation of isoquinolines from ethoxyvinyl pyridines
Authors: Bracher Franz , Mink Kathrin 
Published: July 2007

AbstractThe 2, 7‐naphthyridine alkaloid neozeylanicine (6) was prepared starting from 3‐bromo‐4‐picoline (1) by side‐chain methoxycarbonylation, Pd‐catalyzed ring acetylation and one‐pot ring anellation in 32% overall yield. Condensation of the intermediate pyridyl enol ether 3 with dimethylformamide diethyl acetal to the enamine 7 was followed by spontaneous electrocyclization to give the isoquinoline 8. On treatment with acid or base 3 was cyclized to the 6(2H)‐isoquinolinone 10.
Synthesis of new substituted 1‐(3‐pyridyl)pyridinium salts and 3,4‐diamino‐2(1H)‐pyridinones
Authors: Gewald Karl , Rehwald Matthias , Müller Heike , Bellmann Peter 
Published: July 2007

Abstract2‐[(Chloroacetyl)amino]acrylonitriles 1 and 3‐[(chloroacetyl)‐amino]propionitriles 4 were allowed to react with pyridine to form the 1‐(4‐amino‐3‐pyridyl)pyridinium salts 3 and 1‐(4‐amino‐5,6‐dihydro‐3‐pyridyl)pyridinium salts 6. Dehydrogenation of 6 with bromine in glacial acetic acid afforded 1‐(4‐amino‐3‐pyridyl)pyridinium bromides 7. Treatment of 3 and 7 with hydrazine hydrate yielded the 3,4‐diamino‐2(1H)‐pyridinones 8. Analogously to other ortho‐diamines, the substituted [1,2,5]thiadiazolo[3,4‐c]pyridin‐4‐one 10, [1,2,5]selenadiazolo[3,4‐c]pyridin‐4‐one 11, and further derivatives were obtained from 8. N‐(Chloroacetyl) derivatives of acetylacetoneimide 13 and 3‐oxo‐3‐phenyl‐2‐(phenylhydrazono)propionamide 17 were treated with pyridine to give 1‐(3‐pyridyl)‐pyridinium salts 14 and 18, respectively.
Solvent dipolarity/polarizability (SPP) of alcoholic solvents
Authors: Catalán Javier , López Vicenta , Pérez Pilar 
Published: July 2007

AbstractThe positive solvatochromism exhibited by 2‐(dimethylamino)‐7‐nitrofluorene (DMANF) and 2‐fluoro‐7‐nitrofluorene (FNF) was used to determine the solvent dipolarity/polarizability (SPP) of 29 saturated aliphatic alcohols, four unsaturated alcohols, an aromatic alcohol, a triol, and water. The SPP values for the alcohols lie at the top of the SPP solvent polarity scale. The SPP values for n‐alkanols decreases with increasing chain length, in contrast to the behavior of n‐alkanes. On the other hand, the polarity of n‐alkanols, like that of n‐alkanes, increases on cyclization. The polarity of m‐cresol (1.0) and of 1,1,1,3,3,3‐hexafluoro‐2‐propanol (1.007) places these solvents at the top of the SPP scale.
Addition and cyclization reactions in the thermal conversion of hydrocarbons with enyne structure, 3 A mechanistic study of the thermal cycloisomerization of 1,4‐diphenyl‐1‐buten‐3‐yne
Authors: Hofmann Jörg , Zimmermann Gerhard , Homann Klaus‐Heinrich 
Published: July 2007

AbstractThe gas‐phase pyrolysis of 1,4‐diphenyl‐1‐buten‐3‐yne (1) was investigated in the temperature range between 600 and 800°C and in the presence of different carrier gases (N2, N2/toluene, H2). By a detailed analysis (GC, GC/MS, GC/FTIR) all volatile reaction products were identified and quantitatively determined. Besides several fragmentation products (substituted benzenes C7–C10) and some carbon‐rich deposits the main products are benzene (4), naphthalene (5) as well as 1‐ (2) and 2‐phenylnaphthalene (3). Under similar conditions 4‐(4‐fluorophenyl)‐1‐phenyl‐1‐buten‐3‐yne (1a) furnished mainly fluorobenzene (4a), naphthalene (5), 1‐ (2a) and 2‐(4‐fluorophenyl)naphthalene (3a). – If sufficient H atoms are available in the reactive gas phase the conversion of 1/1a is predominantly controlled by radical processes. The cycloisomerization of 1/1a presumably starts with previously formed vinyl radicals, which might initiate a multi‐step reaction cascade involving a 1,x‐H shift and homoallyl reactions. However, if the reaction system is poor in H atoms (or other chain carrier radicals), a cycloisomerization path via vinyl‐idene carbene species and their subsequent stabilization by intramolecular 1,6‐C,H insertion into 3/3a obviously dominates the reaction events. It is concluded that the 1,2‐dihydro‐2‐phenyl‐1‐naphthyl radicals 19/19a and the 1,2‐dihydro‐1‐phenyl‐2‐naphthyl radicals 21/21a are important intermediates which are not only precursors of the aromatics 2/2a and 3/3a but also thought to be key intermediates for the most important degradation products 4/4a and 5.
Asymmetric synthesis of β‐amino acids and α‐deuterated β‐amino acids via conjugate addition of homochiral amidocuprates
Authors: Sewald Norbert , Hiller Klaus D. , Helmreich Brigitte 
Published: July 2007

AbstractConjugate addition of homochiral amidocuprates based on N‐[(R)‐1‐phenylethyl]trimethylsilylamine or bis[(R)‐1‐phenylethyl]amine to α,β‐unsaturated esters provides an efficient methodology for the asymmetric synthesis of β‐amino acids. Trapping of the intermediate enolate with D2O yields α‐deuterated β‐amino acids with excellent stereoselectivity.
Synthetic microbial chemistry, XXVIII. Synthesis and absolute configuration of (−)‐koninginin A
Authors: Mori Kenji , Abe Kaoru 
Published: July 2007

AbstractThe absolute configuration of the microbial metabolite (−)‐koninginin A (2‐hexyloctahydro‐2H‐3,9a‐epoxy‐1‐benzoxe‐pine‐6,9‐diol, 1) is shown to have the configuration 2S,3S,6R,9S by its synthesis employing the Sharpless asymmetric dihydroxylation.
Unsaturated hetero chains, IV. Synthesis, structure, and protonation of 1‐oxa‐3‐azahexatrienes
Authors: Moldenhauer Jens‐Peter , Möller Manfred H. , Rodewald Ute , Würthwein Ernst‐Ulrich 
Published: July 2007

AbstractDifferently substituted 1‐oxa‐3‐azahexatrienes3were synthesized either by acylation ofN‐silyl‐1‐azabutadienes1or by a four‐step‐one‐pot procedure starting from the nitriles5, involving a Wittig‐Horner‐Emmons‐type olefination as the key step. Both methods allow the isolation of the highly reactive compounds3.The configuration and conformation of31in the crystalline state by X‐ray diffraction were determined, indicating an (E) configuration of the CC bond and agaucheconformation of the CNCO subunit. The reactivity of compounds3towards tetrafluoroboric acid was studied. Protonation takes place exclusively at the nitrogen atom leading to the 1‐oxa‐3‐azoniahexatriene salts10.Quantum‐chemical ab initio model calculations for all possible structures of the parent substances C4H5NO9and C4H6NO+14–16were performed in order to obtain quantitative data regarding the structural and dynamic behavior of these highly flexible molecules in the gas phase.
Regioselective ring opening of oxetanes by hydrogenolysis. – A convenient method for the carbohydroxylation of enol ethers
Authors: Bach Thorsten 
Published: July 2007

AbstractHydrogenolysis of the 2‐aryl‐3‐(silyloxy)oxetanes 1, 2, 5, and 9 in the presence of Pd(0) catalysts (Pd/C) yields 1,2‐diols as ring‐opened products almost quantitatively (82–98% yield). In combination with the preceding photocycloaddition it facilitates the regio‐ and stereoselective carbohydroxylation of silyl enol ethers (total yield: 43–74%). In the case of β‐substituted silyl enol ethers (R1 = alkyl) the reaction sequence leads to a single diastereomeric product (4, 6, 10) in a simple two‐step procedure. Acid‐sensitive substrates such as the dioxolane 1g or the dihydrofuran‐derived oxetane 11 are mildly cleaved in the presence of Pd(OH)2. As demonstrated by selected examples (13, 16, 18) the produced 1,2‐diol remains silyl‐protected if Pd(OH)2 is employed as a catalyst for the hydrogenolysis. In the latter case the silyl protective group stays at the tertiary hydroxy group to which it has been attached in the oxetane, but silyl migration may intervene as was found in the case of the sterically congested oxetane 18.
Bildungsenthalpie und Stabilisierungsenergie des Pentamethylcyclopentadienyl‐Radikals
Authors: Roth Wolfgang R. , Hunold Frank 
Published: July 2007

Heat of Formation and Stabilization Energy of the Pentamethylcyclopentadienyl RadicalFrom the thermolysis of 1 in the presence of 1–60 bar oxygen between 70 and 100°C the activation energy for its dissociation is found to be 27.9 kcal · mol−1. Combining this result with the enthalpy of formation of 4 and a forcefield value for 1 leads to DH° (Me5C5‐H) = 74.1 kcal · mol−1 and ΔH (2) = 16.1 kcal · mol−1, which differs by 5.4 kcal · mol−1 from a value published recently by Walton[1]. The low dissociation enthalpy of 1 is caused only by the relieve of 28 kcal · mol−1 of strain. With an intrinsic radical stabilization energy (IRSE) of 17.3 kcal · mol−1 for 2 there is no justification for an extra stabilization due to cyclic conjugation.