On distribution of molecular weight in anionic polymerizates of caprolactam

Measurement has been made of the dependence of the molecular weight distribution on the ratio of the catalytic system components and on the polymerization time for polycaprolactam obtained by anionic polymerization. A bimodal character of the curves was observed for products made using molar ratios of activator (N-benzoylcaprolactam) to initiator (sodium dihydro-bis(methoxyethoxy)aluminate) of 1:1 and 1:3, when the polymerization times were less than 1 hr. This course is explained by the influence of fast side-reactions, mainly condensations. For a ratio of 3:1 of the components of the catalytic system, smooth integral distribution curves are obtained, accounting for a very fast decrease in the strong base concentration in the initial stages of the polymerization.     

Conformations of the ten-membered ring in 5,10-secosteroids I. X-ray and NMR. Analysis of (E)-3 β-hydroxy-5,10-seco-1(10)-cholesten-5-one esters

X-ray structure determination of the p-bromobenzoate 2b of one of the (E/Z)-isomeric 3β-hydroxy-5,10-seco-1(10)-cholesten-5-ones confirmed the (E)-configuration proposed previously and showed the cyclodecenone ring to adopt an extended crown conformation of type A ₁ (Fig. 9). Analysis of the ¹H- and ¹³C-NMR. spectra of acetate 2a revealed that in solution the ten-membered ring of this steroid exists in at least two distinct forms, the predominant (about 85%) corresponding to the solid-state conformation of 2b (= A ₁), and the minor most likely to B ₂ (Fig. 9). From NMR. data the energy difference between the two species and the relevant activation energy were estimated. A number of conformational force field calculations using a simplified partial structural model was performed; but the computed energy differences between the various possible conformations do not reproduce the effective situation, neither in solution nor in the crystal lattice, indicating that additional effects such as the transannular interaction of the double bond with the carbonyl group may strongly influence the thermodynamic stability of the system. The conformations deduced were used to rationalize the stereochemical course of different chemical reactions of 2a .     

Electronic states of general mixed crystals

Up to now molecular-orbital calculations of the electronic states of linear mixed crystals have been concerned only with binary systems such as AB, AB₂, and A₂B₂. The purpose of the present treatment is to extend this work to crystals whose elementary cells contain any number of different atoms in any ordered sequence. The formulation of this general theory is based on the resolvent method. Although the approach enables the general properties of delocalized and localized states to be discussed, the more simple cases already solved in the literature can still be easily derived from the general equations. Furthermore, the classification of Tamm and Shockley states retains its significance, even when other kinds of states can occur and various transitions between the clear cut cases can exist. As in earlier investigations, the chemisorption states are related to surface states and have similar properties. The resolvent method is summarized in the Appendix and its connection with the partition technique is shown.     

Photometrische Bestimmung von Nitrit mit Rivanol

Zusammenfassung In der vorliegenden Arbeit wurden die Reaktionsbedingungen zur colorimetrischen Bestimmung von Nitrit mit Rivanol untersucht. Die Bestimmung ist einfach durchzuführen und für Nitrit weitgehend selektiv. Die Farbenintensität ist von der Konzentration der salpetriger Säure linear abhängig.     

Aproximate pairing properties of SCF solutions in highly symmetric heteroatomic systems

Approximate pairing properties are proved for the Hartree-Fock solutions for highly symmetric heteroatomic molecules. These molecules have an alternant topology and are built from two kinds of atoms in such a way that by an operation the atoms of one kind go over into the atoms of the second kind and vice versa.

---

Zusammenfassung Es werden genäherte alternierende Eigenschaften für Hartree-Fock-Lösungen hochsymmetrischer heterocyclischer Moleküle abgeleitet. Diese Moleküle haben eine alternierende Topologie, sie sind aus zwei Sorten von Atomen in solcher Weise aufgebaut, daß die Atome der ersten Sorte in die Atome der zweiten Sorte — und umgekehrt — transformiert werden können.

---

Résumé Des propriétés d'accouplement orbital approché sont prouvées pour les solutions de type Hartree-Fock des molécules hétéroatomiques hautement symétriques. Ces molécules ont une topologie alternante et sont formées de deux classes d'atomes de telle sorte qu'il existe une opération interchangeant les atomes des deux classes.

---

---

Supported in part by a grant to The Johns Hopkins University from the Petroleum Research Fund of the American Chemical Society.     

SPECTROCSOPIC STUDIES OF PURINES—III. PROPERTIES OF PURINES SUBSTITUTED AT THE SIXTH AND NINTH POSITIONS*

Abstract— We have investigated the effects of solvent and pH on the absorption and emission propertied of various 6- and 9-substituted purines as a means of examining the nature of the directed not only at deteriming the relative energies of (π,π*) and (π,π*) states, but in particular, at examining the nature and energies of the two lowest-lying (π,π*) states. For examplem, the attachment of a methyl or ribosyl group to the N9 of purine does not change the relative energies of the lowest-lying (π,π*) and (π,π*) states; thus, the latter is the singlet of lowest energy. However, the lowest singles in derivatives formed by substitution at C6 are(π,π*) states—i.e. there is no long-wavelength tail in the absorption spectra and florescence is comparable in intensity to phosphorescence. Further the absence of emission from neutaral adenine at room temperature is due to temperature quenching. Both lowest (π–π*) transtions. are contained under a common envelope and cannot be resolved in the absorption spectra. The shoulder observed in some of these compounds on the long-wavelength slope of absorption envelope is vibrational in nature. Consideration of the effects of solvents on absorption and the analysis of luminescence spectra make it possible to locate the relative position of these (π–π*) transitions within the common envelope. In compounds with an -H on N9 and a free (aza) N1 (e.g. adenine, anionic hupoxanthine) the weaker, solvent-sensitive (W) band has a higher energy then the more intense, solvent-insensitive (S) band. When N1 is protonated, (e.g., in hypoxanthine or cationic adenine) and/or when methyl or ribosyl is substituted at N9, the order of these bands is inverted due ot a red shift of the W band. This shift is most apparent in the 9-substituted hypoxanthines, where in non-polar solvents the W band can be readily resolved in the absoption spectra. This inversion results in a red shift of both fluorescence and phophorescence and an increase of the P/F ratio. When chlorine or iodine is attached at C6 only phosphorescence having a very short lifetime appears due to heavy atom enhancement of single—triplet transitions.     

LOW-TEMPERATURE LUMINESCENCE SPECTRA AND FLUORESCENCE LIFETIMES OF POLYCYTIDYLIC ACID IN POLYALCOHOLIC GLASSES

Abstract— Corrected emission spectra and fluorescence lifetimes of polycytidylic acid in ethylene glycol: water glass at low temperatures are reported. Luminescence properties observed exhibit a strong dependence on pH and temperature. At neutral pH a vibronic structure of a blue part of the fluorescence spectrum is revealed when temperature is changed from 77 to 10 K, confirming that a monomer component of fluorescence is present. There is also a strong difference in decay of a red-shifted excimer fluorescence at 10 K at pH 7 and pH 3.9, reflecting a different protonation of cytosine residues and different conformations of polynucleotides in such conditions.     

Thermal analysis of polyaniline poly(N-vinylpyrrolidone)-stabilized dispersions

The polyaniline dispersions stabilized with poly(N-vinylpyrrolidone) (PANI/PVP) were synthesized by oxidative polymerization with different mass ratios of PANI and PVP and different molar concentrations of the components in the polymerization mixture. The composite powders prepared from colloidal PANI/PVP dispersions were characterized by thermogravimetry and differential thermal analysis. The change in the ratio of PANI and PVP as well as the starting molar concentrations of aniline hydrochloride and oxidant has influence on the resulting properties of the dispersions. Concerning the doping, the results show that PANI/PVP powders are stable up to approximately 160 °C. Degradation of polymer chains starts at temperatures above 250 °C. The PANI/PVP composite powders with lower content of PANI exhibit slightly higher thermal stability. Further, colloidal PANI/PVP dispersions were screen-printed on aluminum foil for infrared spectroscopic characterization and on poly(ethylene terephthalate) foil for electrical measurements. The sheet resistance of printed layers measured by two-point probe was of the order of tens to thousands of kΩ sq^?1. The influence of both the change in the composition and the drying temperature is discussed.     

13,14-Seco-steroids: A New Type of Modified Steroids Containing a Nine-Membered Ring

Oxidations of 14α-hydroxy-5α-cholestan-3β-yl acetate ( 5 ) with lead tetraacetate under thermal or photolytic conditions or in the presence of iodine proceed mainly by fragmentation of the C(13)−C(14) bond to give as the primary products the 13,18-didehydro-13,14-seco derivative 6 and the (E )-Δ¹²-13,14-seco ketone 11 , respectively. Further transformations of these compounds under conditions of their formation afforded, in addition, the acetoxy derivatives 7 – 9 (from 6 ), and the D-homo-C-nor compound 12 and (12R,13R)-epoxide 13 (from 11 ). Unexpectedly, the photolytic lead-tetraacetate oxidation of 5 resulted partly (to ca. 20%) in a reversible fragmentation involving scission and recombination of the C(8)−C(14) bond followed by formation of the 14β,22-ether 10 . Possible mechanisms for the observed transformations are discussed.     

Radical additions to fluoro-olefins. photochemical mono-fluoroalkylation and sequential bis-fluoroalkylation of oxolane

Oxolane was fluoroalkylated by its photoadditions under atmospheric pressure. Monofluoro-alkylations were carried out with hexafluoropropene (1) and perfluorovinyl ethers C₃F₇O-[CF(CF₃)CF₂O]_n-CF = CF₂ (24, n = 0–2) by direct photoexcitation of the olefins to give high yields of addition products 9–12 (81–94%). The reactions were completely regioselecti ve at the oxolane molecule and almost completely regioselective (93–99%) at the double bond of fluoro-olefins; no bis-fluoroalkylated oxolanes were detected. The completely selective introduction of a second fluoroalkyl into position 5 of the oxolane molecule was accomplished by acetone-sensitised photoaddition of 2fluoroalkylated oxolanes 9,10 to fluoro-olefins 1 and 2. Byproducts from reactions of the dimethylketyl radical which is formed in the initiation step were isolated and have given some evidence about the reaction mechanism that is discussed.