1A1⇔5T2 Spin Transition in Heterometallic Solid Phases FexNi1-x(Htrz)3(NO3)2 · H2O (Htrz = 1,2,4‐Triazole)

Solid phases Fe_xNi_1-x(Htrz)₃(NO₃)₂ · H₂O (0.4 x 0.8$) and Ni(Htrz)₃(NO₃)₂ · H₂O were synthesized and studied. The phases were studied by means of magnetochemistry, powder Xray difraction analysis, and electronic and IR spectroscopy. The heterometallic phases are described by the stoichiographic method of differentiating dissolution (DD). The values of x were determined by two methods — atomic absorption and DD. Magnetochemical data showed that the solid phases exhibit a hightemperature ¹A₁ ⁵T₂ 0.5 x 0.8 and disappears at x = 0.4. The spin transition is accompanied by thermochromism (color changed from pink to white at 0.6 x 1 and from pink to light lilac at x = 0.5). A decrease in x leads to a decrease in the temperature of the forward (under heating T_c ) and reverse (under cooling T_c ) transitions, a decrease in hysteresis value ( T_c), and a smearing of the spin transition.     

Ferromagnetische Phase in Produkten des Kochprozesses von Cd(OH)2/Fe(OH)3

In the system CdO·xFe₂O₃ formed from co-precipitated and boiled hydroxides of Cadmium(II) and Iron(III) the following can be identified by X-ray study: atx0.8-besides the Cd(OH)₂ phase--Fe₂O₃, at 1.5x0.8 fine crystalline -Fe₂O₃ and traces of -Fe₂O₃, at 4>x>1.5 both modifications, i.e. -Fe₂O₃ and -Fe₂O₃, and atx>4 only -Fe₂O₃.The course of specific magnetisation as a function of composition confirms the X-ray findings.

---

---

Mit 3 Abbildungen     

Thermal analysis of 1-Hydroxiethylidenediphosphonic acid and its salts

1-Hydroxyethylidenediphosphonic acid and its tetrasubstitutcd Li, Na, K, Rb, NH₄, Ca and Ba salts were synthcsized and their thermal behaviour was studied under non-isothermal conditions by simultaneous TG-DTG-DTA at 20–1000 C. The following thermal transformations were observed: loss of crystallization water, melting in the case of the acid, and intramolecular dehydration in the case of the salts, leading to the corresponding unsaturated derivatives. From the free acid, its acidic salts and the neutral ammonium salt, long-chain polycondensates are formed through intermolecular dehydration.

---

Zusammenfassung 1-Hydroxyethyldiphosphonsäure und ihr Li-, Na-, K-, Rb-, NH₄-, Ca- und Ba-Salz wurden dargestellt. Ihr thermisches Verhalten wurde durch simultane TG-DTG-DTA unter nichtisothermen Bedingungen bei 20–1000 C untersucht. Folgende thermische Umwandlungen wurden beobachtet: Verlust von Kristallwasser, Schmelzen (nur bei der freien Säure), intramolekulare Wasserabspaltung (nur bei den Salzen) zu ungesättigten Verbindungen. Die freie Säure, die sauren Salze und das neutrale Ammoniumsalz bilden unter intermolekularer Wasserabspaltung langkettige Polykondensate.

---

1- , , , , , . - . , , , . , , .

     

Zwitterionic [(H3NCH2C≡CC≡CCH2NH3)]Cu2Cl4 π-Complex: Template Synthesis and Crystal Structure

Crystals of the [(H₃NCH₂CCCCCH₂NH₃)]Cu₂Cl₄ -complex, formed in the oxidative dimerization of propargylammonium cations, were obtained by ac electrochemical synthesis from CuCl₂ · 2H₂O and propargylammonium chloride ([CCCH₂NH₃]Cl) and studied by X-ray diffraction analysis (DARCh automated diffractometer, MoK radiation, /2 scan mode; 2275 reflections with F 4(F), R = 0.048). Crystals are monoclinic: space group B2/b, a = 19.591(6) Å, b = 7.299(3) Å, c = 8.636(3) Å, = 106.83(3)°, Z = 4. The structure consists of individual [(H₃NCH₂CCCCCH₂NH₃)]Cu₂Cl₄ moietes united through the elongated Cu···Cl contacts (2.827(5) Å) into chains oriented along the [010] direction. The bond of the centrosymmetric propargylammonium dimer is -coordintated by copper(I) atom and is elongated to 1.227(6) Å.     

Determination of α and β parameters in approximate SCF MO theories

The formula proposed by Linderberg for the evaluation of the resonance integral is further investigated. Consistency requirements for the parameters lead to an explanation of the Wolfsberg-Helmholz form for. The simple assumption that is proportional to the overlap integral is improved. The dependency of a and values on the distance in a diatomic molecule in this approximation is presented and discussed.

---

Zusammenfassung Linderbergs Formel zur Berechnung des Resonanzintegrals wird weiter untersucht. Konsistenzforderungen für die-Parameter führen zu einer Erklärung der Wolfsberg-Helmholz-Form für. Die einfache Annahme, daß dem Überlappungsintegral proportional ist, wird verbessert. Die Abhängigkeit von- und-Werten vom Atomabstand in einem zweiatomigen Molekül wird in dieser Näherung angegeben und diskutiert.

---

Résumé Etude de la formule proposée par Linderberg pour le calcul de l'intégrale de résonance. Des nécessités de cohérence pour les paramètres conduisent à une explication de la formule de Wolfsberg-Helmholz pour. L'hypothèse simple selon laquelle est proportionnel à l'intégrale de recouvrement est améliorée. On présente en la discutant la dépendance à la distance des valeurs de et de dans une molécule diatomique dans cette approximation.

     

Charge Accumulation in Nanoheterogeneous Iridium Oxide Films

Iridium oxide films with different values of crystallinity degree K are synthesized. Properties of the films and their morphological features are examined. The charging of the films in a 1 M H₂SO₄solution is studied voltammetrically. The most amorphous films (K = 0.08–0.26) acquire the largest overall charge q(in a fixed potential range) relative to films with higher crystallinity degrees; however, the qvs. K dependence is not additive, and the charge remains virtually invariant beginning with K 0.26. The contribution of slow charging processes, which is quite perceptible in the amorphous films, is absent in samples with higher crystallinity degrees, which have faster charge kinetics. The fast charging processes, which are not limited by diffusion, occur in boundary regions of IrO₂crystallites (and/or the oxide part of a crystalline hydrated iridium oxide) and the amorphous phase. The transport of charge-compensating ions in the boundary regions occurs without considerable complications, as in the loose network of amorphous phase IrO₂· xH₂O. The assumption about the formation of a metallic highly-conducting IrO₂cluster at K 0.26 is substantiated. The cluster rules out large resistances in the course of charge transport, which is a possible reason for the slow charging of amorphous films with K < 0.26.     

The identification of small amounts of sugars by means of X-ray diffraction patterns

Summary The identification of small amounts of sugars by their X-ray powder diagrams is suggested as a most simple and practical method in routine analysis.It is especially valuable in working with minute amounts of material, and has proved very useful for the final identification of chromatographically-separated sugars.The characteristics of the powder diagrams of a number of monosaccharides of special interest to the physiological chemist are reported in detail. The substances thus investigated are- and-D-glucose and-glucose monohydrate,- and-D-galactose,- and-D-mannose,D-fructose,D-glucuronolactone,- and-D-glucosamine hydrochloride,- and-D-galactosamine (chondrosamine) hydrochloride,-L-fucose, andD-ribose. For various reasons arabinose, lyxose, and xylose have also been included.It is clear from the powder diagrams of the galactoses that the crystalstructure earlier ascribed to-galactose is that of-galactose.A single-crystal study of-glucosamine hydrochloride was carried out by theWeissenberg technique. The crystal-dimensions obtained agree with those earlier found byCox et al^{5, 7}.The optical rotation of chondrosamine hydrochloride was found to be [] _D ^20° = - 135° - 93° - 39°, the first value being considerably higher than that given for the-form byLevene. A method for the preparation of-mannose is described.

---

Zusammenfassung Die Identifizierung kleiner Mengen verschiedener Zuckerarten mit Hilfe ihrer Röntgen-Pulverdiagramme wird als einfache und praktische Routinemethode vorgeschlagen.Diese Methode ist besonders wertvoll, wenn nur kleine Substanzmengen zur Verfügung stehen, und hat sich für die endgültige Identifizierung von chromatographisch getrennten Zuckern als sehr geeignet erwiesen.Die Einzelheiten der Pulverdiagramme folgender physiologisch-chemisch bedeutungsvoller Monosaccharide werden mitgeteilt:- und-D-Glukose und Glukosehydrat,- und-D-Galaktose,- und-D-Mannose,D-Fruktose,D-Glukuronolakton,- und-D-Glukosaminhydrochlorid,- und-D-Galaktosamin-(Chondrosamin)-hydrochlorid,-L-Fukose, dieD-Pentosen Arabinose, Lyxose, Ribose und Xylose.Aus den Pulverdiagrammen der Galaktosen geht deutlich hervor, daß die Krystallstruktur, die früher der-Galaktose zugeschrieben wurde, tatsächlich diejenige der-Form ist.Die Untersuchung eines Einzelkristalles von-Glukosaminhydrochlorid wurde nach derWeissenberg-Technik ausgeführt. Die erhaltenen Werte stimmen mit den früher vonCox und Mitarbeitern gefundenen überein.Die optische Drehung des Chondrosaminhydrochlorids wurde zu [] _D ^20° = + 135° + 93° + 39° gefunden. Der erstgenannte Wert ist größer als der entsprechende, vonLevene angegebene Drehungswert.Eine Methode zur Darstellung von-Mannose wird beschrieben.

---

Résumé On propose une méthode de routine simple et pratique pour l'identification de petites quantités de divers sucres au moyen de leur diagramme de poudres aux rayons X. Cette méthode est particulièrement précieuse quand on n'a que de petites quantités de matière à sa disposition et elle s'est montrée très convenable pour l'identification finale de sucres séparés par chromatographie. Des particularités des diagrammes de poudres des monosaccharides suivants intéressent le chimiste physiologiste: et-D-glucose et hydrate de glucose, et-D-galactose, et-D-mannose, D-fructose,D-glucuronolactone, chlorhydrate d' et-D-glucosamine, chlorhydrate d' et-D-galactosamine (chondrosamine), l'-L-fucose, lesD-pentoses, l'arabinose, le lyxose, le ribose, le xylose. Des diagrammes de poudres des galactoses découle clairement le fait que la structure cristalline qui fut attribuée précédemment à l'-galactose est celle de la forme. L'expérience sur un cristal unique de chlorhydrate d'-glucosamine a été effectuée d'après la technique deWeissenberg. Les valeurs obtenues concordent avec celles trouvées précédemment parCox et ses collaborateurs. Le pouvoir rotatoire du chlorhydrate de chondrosamine a été trouvé égal à _D ²⁰ = + 135° + 93° + 39°. La première valeur est plus grande que celle donnée parLevene. On décrit une préparation de l'-mannose.

---

---

With 3 figures.     

Etude par viscosité et autodiffusion de solutions aqueuses de divers n-alkyl-benzènesulfonates

Resumé Les propriétés physico-chimiques de solutions aqueuses de différents alkyl-p-benzènesulfonates de pureté contrôlée ont été déterminées par diverses méthodes: solubilité, viscosité, autodiffusions. Les micelles formées par len-octyl-p-benzènesulfonate de sodium (C₈ SO₃ Na) et len-dodécyl-p-benzènesul-fornate de sodium (C₁₂ Na) sont globulaires dans tout le domaine de concetration exploité; les micelles (C₈ SO₃ Na + C₁₂ SO₃ Na) sont de taille proche de celles de C₈ SO₃ Na.La détermination du nombre de contre-ions liés aux micelles de C₈ SO₃ Na confirme cette structure.

---

Summary Various methods, i. e. solubility, viscosity and self-diffusion have been employed to determine the physico chemical parameters of aqueous solutions of puren-alkyl-p-benzene-sulfonates. Micelles of sodiumn-octyl-p-benzene sulfonate (C₈ SO₃ Na) are of globular shape; mixed micelles formed by these compounds (C₈ SO₃ Na + C₁₂ SO₃ Na) show a very slight swelling compared with C₈ S03 Na micelles.The degree of counter-ion association of C₈ SO₃ Na micelles is in good accordance with a globular shape of the micelles.

---

Zusammenfassung Löslichkeit, Viskosität und Selbst-Diffusion wurden benutzt, um physikalisch-chemische Parameter von wäßrigen Lösungen reinern-Alkyl-p-benzenesulfonate zu bestimmen. Mizellen von Natriumn-Oktylpbenzenesulfonar (C₈ SO₃ Na) haben eine globulare Form; Mischmizelle von C₈ SO₃ Na und C₁₂ SO₃ Na zeigen eine sehr geringe Quellung im Vergleich mit Mizellen von C₈ SO₃ Na.Der Grad von Gegenionenassoziation zu C₈ SO₃-Mizellen ist in guter Übereinstimmung mit einer globularen Form der Mizellen.

---

---

Avec 6 figures et 7 tableaux

---

The Lund Institute of Technology, Lund (Suède).

---

Groupe de Dynamique des phases condensées, USTL.     

Catchment region partitioning of energy hypersurfaces,I

The space of internal coordinates of a molecular system is partitioned into catchment regions of various critical points of the energy hypersurface. The partitioning is based on an ordering of steepest descent paths into equivalence classes. The properties of these catchment regions and their boundaries are analyzed and the concepts of chemical structure, reaction path and reaction mechanism are discussed within the framework of the Born-Oppenheimer and energy hypersurface approximations. Relations between catchment regions and the chemically important reactive domains of energy hypersurfaces, as well as models for branching of reaction mechanisms, caused by instability domainsD , 1, are investigated.     

Marginal electron density and density-difference functions

Summary For visual analysis of the density reorganization and distortion, the one-dimensional cut (x, y ₀,z ₀) and the two-dimensional cut (x, y, z ₀) of the three-dimensional electron density difference function (x, y, z) are frequently employed. However, these cut functions do not satisfy any sum rules in contrast to the original difference function (x, y, z). To avoid this difficulty, the use of the marginal electron density functions _x (x) and _xy (x, y) and their difference functions _x (x) and _xy (x, y) is proposed. The marginal densities are condensation of the three-dimensional density onto a particular plane or line of our interest, and they satisfy the sum rule (i.e., the conservation of the number of electrons) exactly. Some basic properties of the marginal electron density are clarified for typical diatomic molecular orbitals. An illustrative application is given for the bonding and antibonding processes in the H₂ system.     

Crystal structure and spectroscopic study of di-μ(1,1)-azido-di-μ(0,0-nitrato)tetrakis(3,5-lutidine)dicopper(II), [Cu(N3) (NO3) (3,5-lutidine)2]2

A mixed ligand 12 complex of copper(II) azide with 3,5-lutidine, namely di-(1,1)-azido-di(0,0)-nitrato)tetrakis(3,5-lutidine)dicopper(II) has been prepared and characterized by X-ray crystallographic and spectroscopic methods. The dimeric molecule, which possesses a crystallographic inversion center, contains two(1,1) bridging azido ligands. Each copper(II) atom in the cyclic Cu₂N₂ unit is further coordinated by two oxygen atoms from two(0,0-nitrato) bridges at Cu-O distances of 2.465(3) and 2.568(3) Å and two nitrogen atoms from the lutidine molecules [Cu-N=2.003(3) and 2.012(3) Å] to give a distorted tetragonal bipyramid. Both azido ligands are linear [N-N-N angle=179.0(4) and asymmetric N-N=1.207(4) and N-N=1.135(5) Å]. The azido bridges produce a rather short Cu Cu distance of 3.013(2) Å. Infrared and electronic data are presented and discussed.     

The incompleteness of Rényi entropies

Since the advent of the notion of mixing character in statistical mechanics, it has been conjectured over and over again that the Rényi entropies provide a mixing isomorphic family, that is: given two probability distributions p and q, the mixing character of q exceeds that of p, m[q]> m[p], if and only if I (q)I (p) for any positive . This conjecture is disproved by means of counterexamples.     

Phase Equilibria in the System CuO-Fe2O3-Sb2O4-O2

Results of X-ray phase analysis were used to construct the phase diagram of the system CuO-Fe₂O₃-Sb₂O₄-O₂ at 1000°C in air. Two Cu_2x Fe_4-3x Sb _x O₆ solid solutions (0 x 0.154 and 0.923 x 1) of, respectively, hematite and bixbyite structure were identified.     

Thermal decomposition of Cu(I) phosphine complexes

The thermal decomposition of Cu(I) phosphine complexes of the general types (CuXPPh₃)₄, [CuX(PPh₃)₂] and [CuX(PPh₃)₃] was investigated.The thermal decomposition of (CuXPPh₃)₄, where X denotes Cl^–, Br^–, I^–, NO ₃ ^– and PPh₃=P(C₆H₅)₃, occurs with formation of a phosphine oxide intermediate. For the remaining complexes this intermediate was not proved in the thermal decomposition.

---

Zusammenfassung Die thermische Zersetzung der Cu(I)-Phosphinkomplexe vom allgemeinen Typ (CuXPPh₃)₄ und [CuX(PPh₃)₂], wie auch [CuX(PPh₃)₃] wurde untersucht. Die thermische Zersetzung von (CuXPPh₃)₄, wobei X=Cl^–, Br^–, I^– und NO ₃ ^– bedeutet und PPh₃=P(C₆H₅)₃, verläuft unter Bildung eines Phosphinoxid Zwischenproduktes, bei den übrigen Komplexen konnte dieses im Laufe der thermischen Zersetzung nicht nachgewiesen werden.

---

Résumé On a étudié la décomposition thermique des complexes phosphine-Cu(I) de formule générale (CuXPPh₃)₄, [CuX(PPh₃)₂], [CuX(PPh₃)₃]. La décomposition thermique de (CuXPPh₃)₄, où X désigne Cl^–, Br^–, I^– et NO ₃ ^– , et PPh₃=P(C₆H₅)₃, s'effectue avec formation d'un oxyde de phosphine intermédiaire; avec les autres complexes, cet intermédiaire n'a pas été mis en évidence au cours de la décomposition thermique.

---

(CuXPPb₃)₄ [CuX(PPh₃)₂] [CuX(PPh₃)₃]. (CuXPPh₃)₄, X=Cl^–, Br^–, I^–, NO ₃ ^– , PPh₃=(₆₅)₃ . .

     

Nucleophilic Substitution at a Four-Coordinate Sulfur Atom: VI. Reactivity of Oximate Ions

The kinetics of the reaction of oximate ions with 2,4-dinitrophenyl p-toluenesulfonate, 4-nitrophenyl p-toluenesulfonate, diethyl 4-nitrophenyl phosphate, and ethyl 4-nitrophenyl ethylphosphonate in H₂O-DMSO mixtures (0 to 95 vol % of DMSO) cannot be described in terms of a single Bro/nsted equation. Regardless of the nature of the reaction center and leaving group, both in water and in 80% DMSO fast leveling of the reactivity of oximate ions is observed, the -effect decreases at pK _a 9.0 and disappears at pK _a 12.0 owing to difference in the solvation of weakly (pK _a 9.0) and strongly basic (pK _a 9.0) oximate ions rather than to change of the transition state. Just unfavorable solvation effects are responsible for the fact that the limiting nucleophilic reactivity of oximate ions (as typical -nucleophiles) is not higher than the reactivity of strongly basic alkoxide ions.     

Polarographische Studien über das Verhalten von p-Benzochinon und p-Benzohydrochinon während der Autoxydation von Äthyllinolat

Zusammenfassung Nach den an Hand der Warburg-Technik durchgeführten Autoxydationsversuchen erweisen sich im Einklang mit früheren eigenen Untersuchungen p-Benzochinon, p-Benzohydrochinon sowie p-Benzochinhydron als Antioxydantien unterschiedlicher Wirkungsstärke und verschiedenartiger Wirkart.Chinon, das schwächste Antioxydans, betätigt sich als Retarder, Hydrochinon mit seiner markanten Verlängerung der Induktionsperiode stellt einen echten Inhibitor dar. Chinhydron sind beide Wirkungen als Retarder und Inhibitor zuzuordnen.Durch eingehende systematische Untersuchungen wird gezeigt, daß die Veränderungen von Chinon, Chinhydron und Hydrochinon während der Autoxydation von Äthyllinolat ohne Störung durch gebildete Hydro peroxyde im lipiden System als reduzierbarer bzw. oxydierbarer Anteil auf polarographischem Wege mit gut reproduzierbaren Ergebnissen und sehr befriedigender Empfindlichkeit bestimmbar sind.

---

Summary According to the autoxidation experiments carried out by means of the Warburg technique,p-benzoquinone,p-benzohydroquinone, and alsop-benzoquinhydrone, in agreement with previous trials by the present writers, exhibit antioxidant actions of different degrees and kinds of action.Quinone, the weakest antioxidant, acts as retarder. Hydroquinone, with its distinct lengthening of the induction period is a real inhibitor. Quinhydrone can function either as retarder or inhibitor.Extensive systematic trials showed that the changes in quinone, quinhydrone and hydroquinone during the autoxidation of ethyl linolate can be determined polarographically in excellent reproducible fashion and with good sensitivity with no interference from the resulting hydroperoxides in the lipid system as reducible or oxidizable portion.

---

Résumé Les essais d'auto-oxydation effectués d'après la technique de Warburg se montrent en accord avec certaines expériences antérieures réalisées avec lap-benzoquinone, lap-benzohydroquinone ainsi qu'avec lap-benzoquinhydrone comme anti-oxydants agissant avec des actions plus ou moins fortes et suivant des processus différents.La quinone, l'anti-oxydant le plus faible, se comporte comme »retardateur«, l'hydroquinone, qui prolonge de manière très accentuée la période d'induction, se présente comme un véritable »inhibiteur«. La quinhydrone se comporte à la fois comme »retardateur« et comme »inhibiteur«.On montre par des recherches systématiques et approfondies que l'on peut doser les variétés de quinone, de quinhydrone et d'hydroquinone pendant l'auto-oxydation du linoléate d'éthyle, comme éléments »réducteurs« ou »oxydants«, par polarographie, avec de bons résultats reproductibles et une bonne sensibilité, sans interférence avec les hydroperoxydes formés dans le système lipide.

---

---

Herrn Prof. Dr.-Ing.G. Gorbach zum 60. Geburtstag in glückwünschender Verbundenheit gewidmet.     

Equilibrium Particle Distribution in the Disperse System with Coagulation and Aggregate Disintegration

Kinetic equations were formulated, which describe coagulation–fragmentation process in a low concentrated suspension flow at a low shear rate. In such a system dispersed phase divided into fine and coarse fractions as the system is brought to equilibrium. Kinetic equations of two-fraction model were formulated. An approximate solution and, in one particular case, the exact solution of these equations were obtained for the equilibrium state. Detailed analysis of equilibrium particle distribution over the mass m was performed for an exponential coagulation kernel = ₀ m and an degenerated disintegration kernel = ₁₂, in which the disintegration frequency is an exponential function of aggregate mass ₁ = ₀ m ⁺ , and the probability of the fragment detachment from an aggregate is independent ofm and decreases exponentially with an increase in mass of a fragment: ₂ = ₀ ^–1exp(–/₀). The equilibrium distribution was shown to exist only at > 0, and in particular, it is described at = = 1 by the f() = ₀₀ ^–1exp(–/₀) and F(m) = Cx ^–1(x + 1)^{2 – 1} e ^–x functions for the particles of fine and coarse fractions (x = m/m ₀, = m ₀/₀, m ₀ and ₀ are the characteristic masses of coarse and fine fractions, respectively). The particle distribution for the fine fraction at 1 is well approximated by the Gaussian distribution exp[–(m – m ₀)²/(4^–1 m ₀₀)].     

The electronic structure of angular polyphenes

SCF calculations of molecular orbitals and electronic transition energies for angular polyphenes of two through nine benzene rings have been made. The calculated sequences of the singlet and triplet energies of the , , , and p bands (Clar's notation) are compared to the limited available experimental data.

---

Zusammenfassung PPP-Rechnungen mit begrenzter Konfigurationenwechselwirkung wurden für die Reihe der angular anellierten Polyphene durchgeführt. Die berechneten -, -, - und p-Banden werden mit den wenigen vorhandenen experimentellen Daten verglichen.

---

Résumé Calculs SCF des orbitales moléculaires et des énergies de transition électronique pour les polyphenés angulaires de deux à neuf cycles benzeniques. Les séries calculées pour les énergies singulet et triplet des bandes -, -, et p (notation de Clar) sont comparées aux quelques données expérimentales disponibles.

     

Calculation of spin densities in odd alternant hydrocarbon radicals

Spin densities in benzyl, allyl, pentadienyl and perinaphthenyl radicals have been calculated with some variants of the simplified McLachlan unrestricted SCF method based on Hückel-type and the SC Hückel-type molecular orbitals. The various estimations of the spin densities were compared one with each other and with the results of more sophisticated methods. It was shown that the SC Hückel basis and Zhidomirov and Schastnev's modification of the McLachlan approach give a best least square fit of the relation a ^exp Q ^calc .

---

Zusammenfassung Die Spindichten von Benzyl-, Allyl-, Pentadienyl- und Naphtenyl-Radikalen werden mit einigen Varianten der uneingeschränkten SCF-Methode in der vereinfachten Form nach McLachlan, die auf den Hückel- und den SC-Hückel-Molekülorbitalen basiert, berechnet. Die verschiedenen Schätzungen der Spindichten werden miteinander sowie mit den Resultaten komplizierterer Methoden verglichen. Es wird gezeigt, daß die SC Hückel Basis und die von Zhidomirov und Schastnev eingeführte Modifikation der Näherung von McLachlan eine beste Näherung nach der Methode der kleinsten Quadrate an die Beziehung a ^exp Q ^calc ergeben.

---

Résumé Les densités de spin ont été calculées dans les radicaux benzyle, allyle, pentadiényle et perinaphthényle à l'aide de variantes de la méthode SCF sans restrictions de spin simplifiée de Mac Lachlan, en utilisant des orbitales de type Hückel et SC Hückel. Les différentes évaluations de densité de spin sont comparées entre elles et avec celles obtenues par des méthodes plus élaborées. On montre que la base SC Hückel et la modification de Zhidomirov et Schastnev à la théorie de Mac Lachlan donnent le meilleur accord au sens des moindres carrés avec la relation a ^exp Q ^cal .