Konformative Beweglichkeit Flexibler Ringsysteme–XI Untersuchungen mit Hilfe der Protonenresonanzspektroskopie Ringinversion bei Methyl- und Alkoxylcyclohexanen

The ring inversion of cyclohexane derivatives with one, two and three pairs of geminal methyl and alkoxyl groups has been studied by investigations of the temperature dependence of the NMR signals. The rate of the inversion depends on the number and the relative positions of the ligand pairs as well as on their size. A single pair of geminal ligands has only a very slight effect on the inversion rate. Two ligand pairs hinder the inversion when they are in the 1 and 4 positions relative to one another, but facilitate it when they are in the 1 and 3 positions. In both cases the effects are smaller with methoxyl groups than with methyl groups. Three ligand pairs significantly increase the inversion rate when they are in the 1, 3 and 5 positions, but reduce it when they are in the 1, 2 and 4 positions. The effect of 1,3 substituents is attributed to an increase in the energy of the ground state of the molecules whereas the effect of 1,4 arranged substituents is attributed to an increase in the energy of the transition state of the chair inversion.     

Substituentenabhängigkeit der Ringinversion des Ungesättigten Siebenringes bei Benzocycloheptenderivaten. Konformative Beweglichkeit flexibler Ringsysteme—XIV: Untersuchungen mit Hilfe der Protonenresonanzspektroskopie

NMR spectroscopy has been used to investigate the ring inversions of the unsaturated seven membered ring system in a total of 20 benzocycloheptene derivatives with 1, 2 and 3 pairs of geminal substituents. For all compounds the inversion of the ring at ? 80°C is ‘frozen’ and at this temperature only one conformation is present in detectable quantity, presumably that of the chair form. The free activation enthalpies ΔG^≠ for the chair inversions lie between 9·9 and 13·7 kcal/mole. For disubstituted and tetrasubstituted benzocycloheptenes the ΔG^≠ values vary according to the positions of the ligands: for disubstituted derivatives ΔG^≠ is largest for the 5-position and smallest for the 3-position. For the tetrasubstituted derivatives the inversion of the ring—compared to that in the comparable dimethyl derivatives—is made more difficult when the ligands are in the 3,6- or 3,7- positions, but is facilitated when in the 3,5- or 4,6- positions. The effect observed in the 3,5- and 4,6- substituted rings is due to transanular repulsion of synaxial substituents, which leads to a flattening of the ring. Such a repulsion does not occur when the ligands are in the 3,6- positions. On the other hand, when the ligands are in 3,7- positions the transanular repulsion leads to a stronger puckering of the chair; the inversion could be hindered by this. For benzocycloheptene the activation energies for the inversions between chair, boat and twist (S, W, T) conformations were determined from model calculations. The best route for the inversion of the chair is the version way S → W via the transitional conformation V₄₅ and V₅₆. The calculated activation energy for this (14·6 kcal/mole) agrees well with the experimentally determined value (13 ± 1·5 kcal/mole). For the pseudorotation W → T a slightly lower calculated value of 11·1 kcal/mole was found.     

Konformative Beweglichkeit Flexibler Ringsysteme–XII Modellrechnungen zur Ringinversion bei Methylsubstituierten Cyclohexanen

For the interpretation of experimental data on the activation energy and free activation enthalpy for the inversion of cyclohexane and its di-, tetra- and hexa-methyl derivatives, model calculations were made to determine the ‘relative’ energies of the ground, intermediate and transition states of the molecules. For this purpose Hendrickson's model was extended so that with internal molecular variables (bond lengths, valence and torsional angles) the topography and the ‘relative’ energy of every possible unsymmetrical conformation could be included. To obtain optimal agreement between the calculated values and the experimental results a total of 17 different combinations of potential functions for deformation of valence angles, torsional angles and H? H interactions were used. By application of the extended calculating procedure it was found that for cyclohexane the half-chair conformation is not, as until now assumed, the only transition conformation in chair inversion, but that there are numerous other unsymmetrical transition conformations with similar energies. The calculations for methyl cyclohexanes showed that for molecules with synaxial arrangement of methyl groups the relative energy of the chair form is considerably increased. The chair form is however still the most stable, even in the case of 1,1,3,3,5,5-hexamethylcyclohexane. The most favourable twist conformations are about 2.6 to 6.5 kcal/mole energy richer. Calculation of activation energies showed that, with synaxial arrangement of two or more methyl groups, the relative energy of the transition conformation is less markedly increased than is that of the ground state, with the result that the activation energy is reduced in comparison with that for cyclohexane.     

Konformative Beweglichkeit Flexibler Ringsysteme—XIII: Untersuchungen mit Hilfe der Protonenresonanzspektroskopie die Konformation des Ungesättigten Siebenringes im Benzocyclohepten und in symmetrisch substituierten derivaten

The confromations of the unsaturated seven membered ring in 4,4,6,6-tetradeuterium-1,2-benzocycloheptene-(1) ( 1 ) and five benzocycloheptene derivatives were determined by NMR spectroscopy. For all investigated compounds at ?80°C only one conformer was present in detectable quantity. By analysis of the NMR data – molecular symmetry, coupling constants and chemical shift – it can be shown that the conformation is always the chair form. The free conformational enthalpy of both the other conformations with boat or twist form of the ring is for all six compounds more than 1.8 kcal/mole. The experimental results agree with those from model calculations: thus for benzocycloheptene, the 5,5-dimethyl derivative ( 2 ) and the 4,4,6,6-tetramethyl derivative ( 4 ) the lowest energy was found for the chair conformation; the second most stable conformations were found to be the boat for 1 and 4 , and the twist form for 2 .     

Die Konformativen Umwandlungen des Ungesättigten Siebenringes in 4.5.6-Trithia-1.2-Benzocycloheptenen-(1) Konformative Beweglichkeit Flexibler Ringsysteme—XVI. Untersuchungen mit Hilfe Der Protonenresonanzspektroskopie

The conformational equilibria and conversions of 4.5.6-trithia-1.2-benzocycloheptene-(1) ( 1 ) and the 3′.6′-dimethoxy-, 3′.6′-dimethyl- and 3′.6′-diphenyl- derivatives ( 2, 3 and 4 ) were investigated by NMR spectroscopy. Solutions of these substances are equilibrium mixtures of two conformers, one presumably having a chair form and the other a boat form. The free enthalpy of the boat conformer ΔG_B is dependent on the size of the substituents (R) in the 3′ and 6′ positions. The ΔG_B values for R = H, OCH₃, C₆H₅ and CH₃ are 1,03, 0,82, 0,50 and ?0,19 kcal/moles, respectively. By slow crystallization one conformer of the substituted trithiabenzocycloheptenes may be obtained in a pure crystalline form. The dimethoxy derivative crystallizes in the chair form, whereas the dimethyl and the diphenyl derivatives crystallize in the boat form. After dissolving the crystals, the conformational equilibrium is restored; at 0°C the half-lifes range from 2 to 15 minutes. By means of the temperature dependence of the NMR spectra two different types of conformational changes may be distinguished experimentally: the slower one is assigned to the inversion of the seven membered ring and the faster one to its pseudorotation. The free enthalpy of activation ΔG_v^≠ of the inversion was determined for 4.5.6-trithia-1.2-benzocycloheptene-(1) by the ‘line-shape’ method and for the diphenyl derivative by the ‘equilibration’ method. Both methods were applied to the other derivatives. The ΔG_v^≠ values obtained by the two different methods agree well with one another. The free enthalpy of activation of the inversion ΔG_v^≠ and of the pseudorotation ΔG_p^≠ both depend on the nature of the substituents. The ΔG_v^≠ values range from 17,9 to 20,5 kcal/mole and the ΔG_p^≠ values are equal to or lower than 11,4 kcal/mole.     

Die Konformeren des 5,5-Dimethyl-3,7-dithia-1,2-benzocycloheptens-(1) und ihre Umwandlungen Konformative Beweglichkeit flexibler Ringsysteme—XV. Untersuchungen mit Hilfe der Protonenresonanzspektroskopie

The temperature dependence of the NMR spectrum of 5,5-dimethyl-3,7-dithia-1,2-benzocyclo-heptene-( 1 ) is described and discussed. This compound occurs in two conformers with different topographies of the seven membered ring. From the chemical shift of the 2 geminal methyl groups (obtained by low-temperature spectra) it can be shown that the ring occurs in one case in the chair form and in the other case in the twist form. The free conformational energy of the twist form is only about 20 cal/mole. Two conformational changes can be distinguished: the conversion between chair and twist forms and the pseudorotation of the twist forms. The free activation enthalpies of the conversion (ΔG_V^≠) and the pseudorotation (ΔG_P^≠) are 12·6 ± 0·1 Kcal/mole (at ?12°C) and 8·3 ± 0·3 Kcal/mole (at ?95°C) respectively.     

Protonenresonanz- und Röntgenstrukturuntersuchungen an unsymmetrisch substituierten Aminoboranen. III—Substituentenabhängigkeit der Struktur

A number of unsymmetrically substituted N-methylaminoboranes, each with a phenyl ring at nitrogen and boron, were synthesized. The ratio of the cis-trans isomers has been investigated by means of ¹H NMR spectroscopy and its dependence on the size of the aromatic moieties and the second substituent on boron is discussed. The structures of the compounds were established from the position of the N-methyl signal and were based on X-ray structure determinations of (4-bromophenylmethylamino) chlorophenylborane and (4-bromo-2-methylphenylmethylamino)chloro(2-methylphenyl)borane. In the case of (methylphenylamino)chlorophenylborane, the isomer with the phenyl group in cis position is highly favoured (90%) in the thermal equilibrium. Substitution of one of the phenyl groups by a 2-methyl- or 2,6-dimethylphenyl group decreases the fraction of the cis isomer. The same occurs when the chlorine substituent at boron is replaced by bromine or the methyl group. In absolute terms, the trans isomers are energetically more stable than the cis isomers only if one of the substituents at boron is a methyl or a 2,6-dimethylphenyl group or if there is a 2-methylphenyl substituent both at the nitrogen and the boron atom. Steric hindrance and electronic repulsion are probably responsible for the observed substitution effects. In addition, these experiments show that the isomer favoured in the crystal also predominates in solution.     

Protonenresonanz-Spektroskopie Ungesättigter Ringsysteme—XIV: Zur Frage der Substituenten-Einflüsse auf die Resonanzfrequenzen und Vicinalen Kopplungskonstanten von protonen in substituierten Benzolen

The substituent effect on proton resonances and vicinal H, H-coupling constants in benzene derivatives is studied using linear regression analysis. The change in shielding observed on substitution, relative to the proton resonance in benzene, Δσ, can be expressed as . This equation enables calculations of substituent effects on the basis of the dipolar and quadratic field effect (E_z, E²) and the π-charge density changes on the neighbouring C-atom (Δρ). The vicinal coupling constants show no correlation with the HMO -π-bond order. A linear regression using the well known dependence of the coupling constant on substituent electronegativity yields where ΔE_α and ΔE_β are the changes in electronegativity caused by substitution in α- or β-position, respectively, to the HCCH-fragment considered.     

Untersuchungen der Symmetrieverhältnisse in äquatorial koordinierten 2:1-Arylazo-CoIII-Komplexen mit Hilfe der Protonenresonanz

The magnetic equivalence of ligand protons was examined with aid of NMR. spectroscopy for a large number of 1:2 Co^III-complexes of tridentated azo dyestuffs forming a representative cross section of the whole class of substances. It was established by this investigation that ligands with a moderately polarised azo group have a particular inclination to form asymmetrical complexes in which the protons of the two ligands are not magnetically equivalent. On the other hand, ligands having a non-polarised or a strongly polarised azo group tend to form symmetrical complexes. In three cases both symmetrical and asymmetrical complexes were isolated. As in previous investigations [1], up to a total of 5 complexes were again observed, which indicates at least two causes governing the symmetry conditions. The phenomena described here could be explained with an alternative coordination of the two azo nitrogen atoms. On the basis of the NMR. results, however, preference is given to an exchange of the azo with the hydrazone form.     

Protonenresonanz-Untersuchungen an N,N-Dialkylaminoboranen. Substituentenabhängigkeit der Rotationsbarriere um die N?B-Bindung 1,2

The substituent dependence of the rotation barriers around the N? B bond in a series of N,N-dialkylaminoboranes was investigated by NMR. It was found that (1) there is a significant dependence on the size of the substituent, which arises from a ‘steric hindrance of mesomerism’ and (2) in certain cases exceptional facilitation of rotation occurs when alkyl groups on the boron atom are replaced by a chlorine atom or a second amino group. The lowering of the rotation barrier by about 10 kcal/mole in bisamino compounds compared with the corresponding monoamino compounds is explained on the basis of a lowering of the double bond character of each N? B bond owing to the participation of two N-atoms in the mesomerism of the ground state. This effect is much larger with amino groups than with chlorine atoms.     

Physikalische und chemische prozesse bei der atomabsorptionsanalyse mit graphitrohröfen—I : Messbedingungen, versuchsanordnung und temperaturmessungen

This is part I of a communication that consists of 3 parts and deals with physical and chemical processes occurring during the atomic absorption analysis with graphite furnaces. The processes are time-dependent because restricted amounts of sample are used. In addition, they are temperature-dependent.In this part, mainly the important measuring conditions are discussed and the experimental facilities are described. Some characteristic examples of the processes are given to draw attention to those processes that should be taken also into consideration when analytical procedures are developed. Such processes are emission by atoms, molecules and radicals, absorption by molecules and radicals, and thermochemical reactions with the furnace material, e.g., formation of intercallation compounds with graphite.In order to study the dependence of the various processes on temperature, different methods for measuring temperatures have been tested as to their suitability and two methods have been applied for measuring the furnace and the plasma temperatures.     

Zur Lokalisierung Funktioneller Gruppen mit Hilfe der Massenspektrometrie. XV—Massenspektren von androstanen mit Hydroxygruppen in den Positionen 3, 16 und 17

Compared with other isomeric androstane triols the mass spectra of those androstane triols with hydroxy groups in positions 3, 16 and 17 are characterized by intense molecular ions. Important fragment ions show the loss of C-15, C-16 and C-17 in the form of a fragment comprising 75 mass units. This ion shows facile loss of the hydroxy group in position 3 in the form of a water molecule producing a [M ? 93]⁺ ion. Further key ions are at m/e 60, 84 and 110. With the aid of three deuterated androstane trioles and high resolution it was shown that these ions contain parts of the D-ring system.     

Abtrennung von Na, K und P mit Hilfe anorganischer Separatoren bei der Neutronenaktivierungsanalyse von biologischem Material

Zusammenfassung Zur Entfernung hochaktiver Komponenten aus neutronenaktivierten biologischen Proben wurden 2 Sorptionsprozesse eingehender untersucht. Zur Abtrennung von ²⁴Na wurde unterschiedlich hergestelltes Hydratisiertes Antimon Pentoxid (HAP), für die Abtrennung von ³²P Zirkoniumphosphat (ZP) getestet. Für die Abtrennung von ⁴²K wurden handelsübliche Titanphosphatpräparate (TiP) benutzt. Aufgrund der Sorptionsversuche und einiger physiko-chemischer Eigenschaften der Präparate wurden die Parameter zur Herstellung und Anwendung dieser Substanzen optimiert. Durch kombinierte Anwendung von HAP, ZP und TiP waren bei den gewählten Arbeitsbedingungen, z. B. bei aktivierten Kartoffelproben, keine dieser 3 störenden Komponenten nachweisbar. Eine halbautomatische Trennapparatur wurde konstruiert, welche aus folgenden Hauptteilen besteht: Destillationsapparatur, Sorptionskolonne, Ionenaustauschersäule, GradientelutionsAufsatz, elektropneumatische Ventile und Fraktionssammler. Die Aufarbeitung der Probe erfolgt ferngesteuert, der Zeitbedarf beträgt ca. 7 h.Frl. I. Berg, Frau E. Haller und Herrn B. Bauer wird für die wertvolle Mitarbeit bei den Untersuchungen gedankt.     

Die Aminoalkylierung von Phtalazinen und Phtalazonen mit Hilfe der GRIGNARD-Reaktion. 4. Mitteilung über GRIGNARD-Reaktionen mit Halogenalkylaminen [1]

Phtalazines and 4(3H)-phthalazones are aminoalkylated in high yield by 3-dimethylaminopropyl-magnesiumchloride. Phthalazines add only one molecule of the GRIGNARD reagent at the C?N-double bond, giving mono-aminoalkylated 1,2-dihydrophthalazines which undergo no further reaction without previous oxydation. Phthalazones react with the carbonyl and the C?N-group yielding in one step di-aminoalkylated dihydrophthalazines. The dihydrophthalazines are easily oxydized with K₃Fe(CN)₆ to the corresponding phthalazines.     

Untersuchungen über das Verhalten organischer Mischphasen 9. Mitteilung Vergleich der binären Systeme Tetrahydrofuran mit Wasser,Methanol und Cyclohexan,Diäthyläther mit Wasser,Methanol und Cyclohexan und Tetrahydrofuran-Diäthyläther

Activities and mixing functions of the following binary systems at 25° C are discussed: 1. mixtures of tetrahydrofuran with water, methanol, and cyclohexane; 2. mixtures of diethyl ether with water, methanol, and cyclohexane, and 3. mixtures of tetrahydrofuran with diethyl ether. Comparison with similar systems shows that in systems containing methanol, the strongest interactions are formation and breaking of hydrogen bonds between alcohol molecules; interactions between methanol and ether molecules play a minor rǒle. Systems containing water exhibit two main kinds of interaction: formation and breaking of hydrogen bonds between water molecules, and formation of hydrogen bonds between water and ether molecules. Deviations from ideality are larger for diethyl ether than for tetrahydrofuran in water and methanol, and smaller in cyclohexane.