Twisted Form Research Articles

1,2,3‐Triazolidine durch Cycloaddition von Aziminen an Olefine

1,2,3‐Triazolidines by Cycloaddition of Azimines to OlefinesAzimines A can undergo [3+2]‐cycloadditions with olefines B to give 1,2,3‐triazolidines C, a class of hitherto unknown heterocycles. The three examples of this reaction realized here involved the azimine 1 with electron‐withdrawing substituents and the olefines 2, 3 and 4 with an electron‐donating substituent, yielding the cycloadducts 5,6 and 7. The triazolidine structure of 5 was established by an X‐ray diffraction analysis. Characteristic for 5 are also: (a) that the three N‐atoms are pyramidal (and thus centers of chirality), (b) that the five‐membered heterocycle takes on a twist (half‐chair) form, and (c) that the regioselectivity of the cycloaddition places the (E)‐substituent of the olefine 2 vicinal to the terminal (Z)‐substituent of the azimine 1. On this basis the constitutions of 6 and 7 are assigned. The spectral properties of the triazolidines 5, 6 and 7, including the 15N‐NMR signals of one example, are compared with those of the related triazane 12.

13C nuclear magnetic resonance and conformational analysis of 5‐chloro‐2‐oxo‐1,3,2‐dioxathianes

AbstractThe 13C NMR chemical shifts in CDCI3 for eight cyclic sulphites, chlorinated at C‐5, are reported. The α‐and β‐deshielding effects and the γ‐shielding effects for the chlorine substituent are compared with similar effects in the 1,3‐dioxane series and with the effects arising from methyl groups in the sulphite series. The study of two conformational equilibria shows that it is difficult to use 13C NMR spectroscopy for the conformational analysis of cyclic sulphites because of the frequent participation of twist forms, with 1,4‐ and 2,5‐axes, to these equilibria.

Ab initio studies on calicene

AbstractOptimum geometries of planar and 90°‐twisted C2v calicene are calculated with single‐configuration STO‐3G and 3‐21‐G wavefunctions. The barrier to ring–ring rotation is computed. Bond alternation is pronounced in the planar form and decreases in the twisted form, while dipolar character increases on twisting.

Theoretical Determination of Molecular Structure and Conformation. XI. The Puckering of Oxolanes

AbstractStructural, conformational and energetic properties of cyclopentane (1) and the seven oxolanes monoxolane (2), 1,3‐dioxolane (3), 1,2‐dioxolane (4), 1,2,4‐trioxolane (5), 1,2,3‐trioxolane (6), tetroxolane (7), and pentoxolane (8) are investigated employing the polarized 6‐31G* basis set at the Hartree‐Fock level of theory. Extensive geometry optimization is carried out within the model of the semirigid pseudorotor. The conformational potentials V of compounds 1–8 are evaluated as a function of the puckering amplitude q and the pseudorotation phase angle Φ. Ring molecules 1 and 8 are free pseudorotors, while pseudorotation is hindered by barriers ≤ 3.3 kcal/mol for oxolanes 2–7. Puckering and inversion barriers increase with the number of O‐O bonds but decrease with the number of ether bridges. Puckered C2‐symmetrical twist forms are the most stable conformations for compounds 2–7 but 6, where highest stability is found for the C2‐symmetrical envelope forms. At room temperature a multitude of conformers of 1–8 coexists either because of free pseudorotation (barriers < RT) or large amplitudes of pseudolibration. These results are rationalized in terms of the rotor potentials of appropriate reference compounds (C2H6, CH3OH, H2O2). A more elegant approach leads to a simple π electron count and an analysis of bonding and antibonding overlap in the π‐type HOMO's. In this way the effects of substituents can be predicted and conformational preferences of the furanose ring in nucleotides, nucleosides and carbohydrates explained. The relative stability of the oxolanes is analyzed by calculating O‐O bond energies, bond‐bond interactions and ring strain for each compound. The lability of the higher oxolanes is traced back to increased ring strain. A new method of the conformational analysis of ring compounds is outlined.

Manifestly parity invariant electromagnetic theory and twisted tensors

We develop here the calculus of twisted tensors and in particular twisted differential forms, treating them as tensors with complementary orientations. These geometrical objects give us the proper language for electromagnetic theory in a 3-space plus time representation. The parity properties of the fields are simplified and many graphical illustrations are given.

Two new mesophases in a chiral compound

Microscopical, miscibility and X-ray studies establish the existence of two new mesophases in the two enantiomers of 1 (methyl)-heptyl terephthalidene bis amino cinnamate. In one of this two mesophases the two enantiomers do not exhibit a total miscibility range; while for the second the untwisted form observed with the racemic mixture has a higher temperature range of stability than the twisted form observed for the pure enantiomers. Information about the structures of the two phases is given and a comparison is made with the S*C and SD phases. Nevertheless the location of these two phases in the sequence of the presently known calamitic mesophases is not yet completely established.

Comparison of the equilibrium geometry of acetylene (C 2H 2) and disilyne (Si 2H 2)

The equilibrium geometry of disilyne is not linear, but is twisted. The potential surfaces of acetylene and disilyne have a critical internuclear distance between the central atoms, where the stable geometry changes from linear to twisted forms the R-dependence of the valence-shell electron energy causes the difference in the structure of the molecules.

Zur Kenntnis organischerLewis-S�uren, 36.Cis?trans-Gleichgewichte und Konformationen von 2,(x)-Dialkyl-1-dicyanomethylencyclohexanen. Wahlweise einfache Darstellung dercis- odertrans-Formen

Knoevenagel condensation of malononitrile withcis- andtrans-2,5-dimethylcyclohexanone (1 c and1 t, respectively) leads to2 c and2 t, respectively, and withtrans-1-decalone to4 t. The equilibria2 c⇌2 t and4 c⇌4 t have been determined as well as, by means of 270-MHz-1H-NMR, the conformations of these four compounds. The dicyanomethylene group is found to induce axial positions of neighbouring alkyl residues on the cyclohexane ring (or when this is impossible, as in the case of4 t, the twist form of the cyclohexane ring). This results in a strong predominance of thecis isomers in the equilibria2 c⇌2 t and4 c⇌4 t whereas thetrans isomers strongly predominate in the equilibria among the starting ketones. This situation allows the optional preparation of2 c or2 t, and of4 c or4 t, from the more stable starting ketone (or ketone mixture). The free conformational energy of the distorted twist form of4 t amounts to 17 kJ/mol.

Über die Konformation yon 1.2.4.5-Tetrathian / On the Conformation of 1,2,4,5-Tetrathiane

Abstract The conformation of 1,2,4,5-tetrathian was determined by means of dynamic NMR spectroscopy. The barrier (ilG+) of the chair/twist equilibration is 14.5 kcal/mol and the chair form is more stable than the twist form in this molecule by 1.4 kcal/mol. These experimental data are in excellent agreement with force field calculations

X‐Ray Diffraction Study of the Diels‐Alder Adduct of 4‐Phenyl‐1, 2, 4‐Triazoline‐3, 5‐Dione with Previtamin D3

AbstractC35H49N3O3, orthorhombic, P212121, a = 7.142 (1), b = 11.873 (4), c = 37.852 (9)Å; V = 3209.7 (15) Å3, Dx = 1.16 Mg m−3 for Z = 4. The structure has been solved by direct methods (MULTAN 80) and refined to a final R value of 0.068 for 1920 observed reflections.The absolute stereochemistry of the title compound is shown in 1; the configuration at the asymmetric carbons is C(20)R, C(17)R, C(13)R, C(14)S, C(9)R, C(6)S and C(3)S. The cyclohexene ring A is in a flattened half‐chair conformation. The tetrahydropyridazine ring B adopts a sofa like conformation with N (33) located under the mean plane of the ring. The six‐membered ring C is close to a D2 twist (boat) form. The cyclopentane ring D adopts a conformation intermediate between a half‐chair (C2 symmetry) and an envelope (Cs symmetry). Finally the urazole ring E is almost flat.

A theoretical investigation of electron relaxation accompanying core ionization in the symmetry forms of ethylene

Relaxation energies accompanying core ionization in the planar and twisted form of the C2H4 molecule have been computed in terms of single orbital contributions by means of the ab initio SCF techniques. It is shown that the 2 eV shift between the core electron binding energies of both symmetry conformers may be attributed to changes in the π-valence electron relaxation when going from the planar to the twisted form of C2H4.

Ultrastructure and nature of secretory proteins in the male accessory gland of Drosophila funebris

The ultrastructural differentiation of the secretory cells and the nature of secretory proteins in the male accessory gland of Drosophila funebris have been studied by electron-microscopic and immunological methods. (1) In the pupae at 1 1 2 days before eclosion, secretory products can be detected in the lumen, even though most glandular cells are at the initial phase of differentiation. At the time of eclosion both main and secondary cells are fully differentiated, but the whole set of five immunologically active proteins are detectable only on the second to third day of adult life. (2) The secondary cells contain giant protein granules, the so-called filamentous bodies, which become partially fused and the filaments assume a twisted form. Randomly dispersed filaments and closely packed filament bundles are also visible in the gland lumen. Antigenic labelling of ultrathin sections and immunoreplica electrophoresis yielded no evidence for the microtubular nature of these filaments. The secretion stored in the lumen contains in addition a large quantity of flocculent proteins which have their origin in the main cells. (3) During the period of high secretory activity in the 7-day-old male flies no vacuolization and disintegration of either the main or secondary cells have been observed. We conclude that both types of cells have the merocrine secretory mechanism. (4) Ultrastructural alterations in the glandular cells confirmed our previous observation that copulation stimulates RNA and protein synthesis.

A comparison of the automorphic representations of GL(3) and its twisted forms

0* Introduction* The theorems are deduced as consequences of the Arthur-Selberg trace formula. The proofs have been patterned after those used in [17] in comparing the representation theory of the groups GL (2) over two distinct fields. The two main theorems of this thesis are as follows. Let F be a nonarchimedean local field of characteristic zero, let G — GL (3, F), and let G be the group of invertible elements in a central division algebra of rank 3 over F. Define admissible irreducible representations π of G and π' of G to be related, and write π ~ π', if Θπ(g) = Θπ,(g') for all pairs of elements g e G and g' e G' which have the same irreducible characteristic polynomial, where Θπ (resp., Θπ,) is the character of π (resp., π ).

Molecular and crystal structure of sophoridine N-oxide

The spatial structure of natural sophoridine N-oxide has been studied by x-ray structural analysis. It has been shown that when sophoridine is oxidized, rings B and C, which have the boat form, are deformed in the direction of the twist form.

The crystal and molecular structure of d1-17β-hydroxy-8α-androst-4-en-3-one (8-isotestosterone)

The molecular conformation of d1-8-isotestosterone has been determined crystallographically. Crystals of the title compound belong to the space group P2 1/c with a = 11.449(4), b = 10.962(4), c = 25.860(5) , β = 100.95(4) 0, with two molecules in the asymmetric unit. The structure has been refined to a final R value of 0.052 for 2227 reflections. Unlike testosterone, which is a flat molecule, its 8-isomer has a folded conformation. The conformations of the ring-B in the two crystallographically independent molecules (A and B) correspond to the twist form and differ significantly from one another.

Structure of potassium sucrose octasulfate heptahydrate

C12H14035SsS-.8K+.7H2 O, M r = 1413.58, orthorhombic, P2~2~2~, a = 16.865 (12), b = 18.649 (5), c = 14.051 (3)A, Z = 4, and D x = 2.12 Mg m -a. In the sucrose moiety, the furanosyl ring takes a 5T 4 twist form while the pyranosyl ring takes a 4C~ chair. The K ÷ ion is surrounded by five to seven O

Empirical Force Field Calculations XIII. The Ring Interconversion Modes of cis‐1, 2, 3, 4, 4a, 5, 8, 8a‐Octahydronaphthalene and its 1α, 4α‐Dimethyl Derivative

AbstractThe inversion of the (half‐chair) chair conformers of cis‐1, 2, 3, 4, 4a, 5, 8, 8a‐octahydronaphthalene (1) and of its 1α, 4α‐dimethyl derivative (2) are studied with molecular mechanics using the white and Bovill empirical force field. It is a multi‐stage process: first the chair form of the saturated ring transforms into a twist conformation, then the (half‐chair) twist form can follow several pseudorotational paths on which the one half‐chair form of the unsaturated ring passes into the other via a boat form, and finally the twisted saturated ring converts into the inverted chair conformation. In 1 the first part of this process is of higher energy (ΔH≠ = 34.4 kJ mol−1) than the lowest pseudorotational path (30.8 kJ mol−1), in 2 it is the pseudorotational part of the inversion that is of somewhat higher energy (34.0 kJ mol−1) than the chair‐to‐twist stage (32.9 kJ mol−1). The methyl substituents cut off low energy pseudorotational paths available to 1 and direct the pseudorotation in 2 to regions of higher energy. The experimental determination of the inversion barrier of 1 yields ΔG≠ = 41.4 kJ mol−1.

ChemInform Abstract: 13C CHEMICAL SHIFTS ‐ SENSITIVE DETECTORS IN STRUCTURE DETERMINATION. 1. 13C NMR STUDIES OF SATURATED HETEROCYCLES. 4. METHYL‐SUBSTITUTED 1,3‐DIOXANES

The 13C chemical shifts for 1,3-dioxane and 50 methyl-substituted derivatives are reported. Substituent effects on them are derived and their magnitude shown to be closely related to the exact ring geometry and other conformational aspects. The results confirm the high chair-twist preference and support the view that 1,4-twist is appreciably more stable than 2,5-twist. Only 2,4-diaxially substituted compounds normally attain a twist form whereas 4,6-diaxial substitution alone is not enough but deform the chair form. A combination of the detailed knowledge on the stereochemistry of the 1,3-dioxane ring and on the type of significant shift parameters leads inevitably to the conclusion that a proper understanding of their interdependence offers a useful tool for conformational and configurational analysis.

Twist form in equilibrium of stereoisomers of 5-phenyl-2,4,6-triisopropyl-1,3,5-dioxaphosphorinane and its derivatives

In the equilibrium of 5-phenyl-2,4,6-triisopropyl-1,3,5-dioxaphosphorinane and its derivatives the stereoisomer with nonequivalent protons on the carbon atoms attached to phosphorus is found predominantly in the twist form.

13C Chemical Shifts — Sensitive Detectors in Structure Determination. 1. 13C NMR Studies of Saturated Heterocycles. 4. Methyl‐Substituted 1,3‐Dioxanes

AbstractThe 13C chemical shifts for 1,3‐dioxane and 50 methyl‐substituted derivatives are reported. Substituent effects on them are derived and their magnitude shown to be closely related to the exact ring geometry and other conformational aspects. The results confirm the high chair‐twist preference and support the view that 1,4‐twist is appreciably more stable than 2,5‐twist. Only 2,4‐diaxially substituted compounds normally attain a twist form whereas 4,6‐diaxial substitution alone is not enough but deform the chair form. A combination of the detailed knowledge on the stereochemistry of the 1,3‐dioxane ring and on the type of significant shift parameters leads inevitably to the conclusion that a proper understanding of their interdependence offers a useful tool for conformational and configurational analysis.