Imaging thin films of nanoporous low-k dielectrics: comparison between ultramicrotomy and focused ion beam preparations for transmission electron microscopy.

Ultramicrotomy, the technique of cutting nanometers-thin slices of material using a diamond knife, was applied to prepare transmission electron microscope (TEM) specimens of nanoporous poly(methylsilsesquioxane) (PMSSQ) thin films. This technique was compared to focused ion beam (FIB) cross-section preparation to address possible artifacts resulting from deformation of nanoporous microstructure during the sample preparation. It was found that ultramicrotomy is a successful TEM specimen preparation method for nanoporous PMSSQ thin films when combined with low-energy ion milling as a final step. A thick, sacrificial carbon coating was identified as a method of reducing defects from the FIB process which included film shrinkage and pore deformation.     

Versatile synthesis of nanometer sized hollow silica spherest

Using the controlled precipitation of silicic acid on functionalized polystyrene latexes, nanometer sized silica-coated spheres could be prepared and subsequently modified to allow dispersion in non-aqueous solvents; removal of the interior polymer by calcination resulted in the formation of hollow silica spheres.     

A Facile Synthesis of Optically Pure (−)-(S)-Ipsenol Using a Chiral Titanium Complex

A stereocontrolled synthetic route to optically pure (?)-(S)-ipsenol ( 1 ), the pheromone of Pityokteines curvidens and various other bark-beetle species is described. Key step of the synthesis is an enantioselective aldol reaction using a chiral titanium–carbohydrate complex (Scheme 1). The carboxylate function of the optically pure β-hydroxy acid 5 thus obtained in mol quantities is then elaborated to the diene moiety by standard methodology (Scheme 2).     

Geltungsbereich und Mechamismus der durch Silberionen katalysierten Propargylester-Allenylester-Umlagerung nach Saucy und Marbet

The mechanism of the catalysis of the reversible (propargyl ester)/(allenyl ester) rearrangement ( 10 ? 11 ) by silver(I) ions was investigated, using optically active and diastereoisomeric esters as well as ¹⁴C- and ¹⁸O-labelling. In order to work with crystalline materials, mainly p-nitrobenzoates ( 10 , 11 : R⁴ = p? O₂N? C₆H₄) were used. In some cases the rearrangement 10 ? 11 was studied using acetates (R⁴ = CH₃). The alkyl substituents R¹, R², R³, were widely varied (cf. Tables 1, 2). The solvents in which the rearrangements were performed were in most cases dry chlorobenzene and 96% aqueous dioxane. Silver tetrafluoroborate, the benzene complex of the latter, and silver trifluoroacetate (in chlorobenzene) as well as silver nitrate (in aqueous dioxane) served as catalysts. The amounts of the silver catalysts used varied between 0,5 and 10 mol-%; reaction temperatures applied were in the range 35–95°, The results obtained are as follows:

• 1 The rate-determining step of the (propargyl ester)/(allenyl ester) rearrangement ( 10 ? 11 ) occurs in a silver(I) complex with the substrates ( 10 , 11 ), which is formed in a pre-equilibrium. This follows from kinetic experiments (cf. Fig. 6, 7, 8, 10) and the fact that the rate of rearrangement (of 10a ) is strongly decreased when cyclohexene is added (cf. Fig. 9). In solvents which are known to form complexes with silver(I) ions the rate of rearrangement (of 10a )is much slower than in solvents with similar dielectric constants but with small capacity for complex formation with silver(I) ions (cf. Table 4). Taking into account what is known about silver(I)-alkene and -alkyne complexes (cf. [18]), it is obvious that the (propargyl ester)/(allenyl ester) rearrangement occurs in a π-complex of the silver(I) ion with the triple bond in the propargyl ester or one of the two C,C double bonds in the allenyl ester, respectively.
• 2 The shift of the carboxyl moiety in the reversible rearrangement 10 ? 11 occurs intramolecularly. p-Nitrobenzoic acid-[carboxyl-¹⁴C] is not incorporated during the rearrangement, neither in the reactant 10 nor in the product 11 and vice versa. A crossing experiment gave no mixed products (cf. Scheme 2, p. 882).
• 3 An internal ion pair can be excluded for the rearrangement 10 ? 11 because the ¹⁸O-carbonyl label in the reactant is found exclusively in the alkoxy part of the product (cf. Scheme 3, p. 886, and Table 9). Thus, the rearrangement 10 ? 11 occurs with inversion of the carboxyl moiety.
• 4 The rearrangement of optically active propargyl esters ( 10g , 10i ) leads to completely racemic allenyl esters ( 11g , 11i ). However, rearrangement of erythro- and threo- 10j -[carbonyl-¹⁸O] (Scheme 3) shows that the stereospecifically formed allenyl esters erythro- and threo- 11j -[¹⁸O]-epimerize rapidly in the presence of silver(I) ions. This epimerization is twice and forty times, respectively, as fast as the rearrangement of the corresponding propargyl esters (cf. Fig. 1–5). During epimerization or racemization the ¹⁸O-label is not randomized (cf. also Scheme 4, p. 898).
• 5 The equilibrium of the rearrangement 10 ? 11 depends on the bulkiness of the substituents R¹, R², R³ and of the carboxyl moiety (cf. Table 2).

Taking into account these facts (points 1–5), the reversible (propargyl ester)/(allenyl ester) rearrangement promoted by silver(I) ions can be described as a [3s, 3s]-sigmatropic reaction occurring in a silver(I)-π-complex with the C,C triple bond in 10 and a C,C double bond in 11 . It is suggested that complex formation in 10 and 11 occurs with the π-bond which is not involved in the quasicyclic (containing six orbitals and six electrons) transition state of the rearrangement (Fig. 11). Thus, the rearrangement is of a type which has recently been called a charge-induced sigmatropic reaction (cf. [26]). Therefore, in our case, the catalysis by silver(I) ions is of a different type from that of transformations of strained cyclic molecules promoted by silver(I) ions (cf. [14] [16] [27]–[31]). Side reactions. Whereas the rearrangement of propargyl esters 10 in presence of silver tetra- fluoroborate in chlorobenzene or silver nitrate in aqueous dioxane leads to the corresponding allenyl esters 11 , the rearrangement of 10 with silver trifluoroacetate, especially in the presence of trifluoroacetic acid, results in the formation of the dienol esters 12 and 13 , which clearly are derived from 11 (see Scheme 1, p. 881). As shown by the rearrangement of 11 in the presence of p-nitrobenzoic acid-[carboxyl-¹⁴C], 12 and 13 arise in part from a not isolated di-p-nitrobenzoate (cf. Scheme 6, p. 905), since radioactivity is found in 12 and 13 .     

Self-Replication of Oligonucleotides in Reverse Micelles

The coupling between the tri(deoxynucleotides) d[(MeO)C-G-Ap] ( 1 ) and d[(NH₂)T_d5′-C-G-] ( 2 ) to yield the phosphoramidate-linked (hexadeoxy-nucleotide) d[(MeO)C-G-Anh⁵′T_d5′-C-G] ( 3 ) was investigated both in aqueous solution and in reverse micelles constituted of CTAB (cetyl(trimethyl)ammonium bromide) in hexane/pentan-1-ol 9:1. No siginificant difference was found concerning the yield and the kinetics of the reaction in the two systems. The coupling between 1 and 2 was also carried out in the presence of the template d[(MeO)C-G-A-T-C-G] ( 4 ), an analogue of 3 , so as to reproduce the conditions of template-directed self replication. It was shown that the trinucleotide coupling in the presence of a template obeys the so-called square-root law both in H₂O and in reverse micelles. No significant difference of the time course of the reaction in H₂O and in reverse micelles was observed. This shows that self-replication of oligonucleotides occurs within geometrically bounded structures, which represents a step forward in the mimicking of minimal life processes.     

Umcyclopropanisierung bei der Tetrabromierung eines tricyclischen Ketons zu 3exo, 4endo, 6exo-Tribrom-7-brommethyl-1,5-dimethyl-tricyclo[3.2.1.02,7]octan-8-on

Transcyclopropanation during the Tetrabromination of a Tricyclic Ketone to 3 exo, 4 endo, 6exo-Tribromo-7-bromomethyl-1,5-dimethyl-tricyclo[3.2.1.0^2,7]octan-8-one Bromination of the tricyclic ketone 1 with an excess of bromine at low temperature gives in approximately 30% yield the highly crystalline tricyclic tetrabromide 2 (Scheme 1). The structure of 2 was established by NMR.- and especially X-ray-analysis (Fig.1). Treatment of 1 with 1 mol-equ. of bromine gives an unstable dibromide, to which the structure 3 was assigned on the basis of its NMR.-spectrum and its further bromination to 2 (Scheme 1). In the course of the tetrabromination of 1 the original cyclopropane ring is opened in the first step ( 1 → 3 ) and another cyclopropane ring is formed in the second step ( 3 → 2 ) (cf. Scheme 3).     

Die spontane Spaltung von 3,3-Diäthyl-5-methylpiperidin-2,4-dion(Methyprylon) in die optischen Isomeren. Eine Rötgenstrukturanalyse eines isodimorphen Systems von Mischkristallen

The Spontaneous Resolution of the 3,3-Diethyl-5-methylpiperidine-2,4-dione (Methyprylon) into its Optical Isomers. An X-Ray Structure Analysis of an Isodimoophous System of Mixed Crystals Repeated recrystallizations from acetone of a racemic mixture of the title compound successively result in a spontaneous resolution into optical isomers [1]. In this process batches of mixed crystals of increased optical purity are formed [2]. This phenomena was investigated on a molecular basis using X-ray diffraction methods. The mixed crystals belong to the space group P2₁2₁2₁ and their diffraction patterns give no indication of major disorders. There is a linear relationship between the changes in unit cell parameters a and b and the optical rotation of the sample. The structures of the mixed crystals from four fractions belonging to two different crystalline modifications have been determined. The molecular shape is such that most of the atomic positions of the two enantiomers superimpose almost perfectly. Occupation factors determined for the asymmetric C- sites agree well with the optical activity of the crystals fraction.     

Quantitative Bestimmung von Mono- und Dienen in Kohlenwasserstoffgemischen

Zusammenfassung Konjugierte Diene und Monoene werden colorimetrisch in Kohlenwasserstoffgemischen durch Kupplung mit diazotiertem p-Phenylendiamin bestimmt. Die Methode ermöglicht auch die Bestimmung beider Kohlenwasserstoffgruppen nebeneinander.

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Summary Conjugated dienes and monoenes may be determined in mixtures of hydrocarbons by colorimetry of the dye obtained by coupling with diazotized p-phenylenediamine. Both groups of hydrocarbons can also be determined in presence of each other.

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Der ESSO-AG Hamburg danken wir für weitreichende Unterstützung der vorliegenden Arbeit und für die Erlaubnis, die gefundenen Resultate zu veröffentlichen.

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Herrn Prof. Dr. C. Mahr zum 65. Geburtstag gewidmet.

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Marxmeier, H.: Diplom-Arbeit, Marburg 1960.

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Wolf, W.: Staatsexamensarbeit, Marburg 1962.     

The polyiodide salts: Pyridinium pentaiodide;β-naphthylammonium pentaiodide; andN-methyl-γ-picolinium heptaiodide. Structures with channel inclusion features

The crystal structures of three polyiodode salts are reported (pyridinium pentaiodide, monoclinic,P2 ₁/m,a=9.221(5),b=12.918(5),c=6.026(4) Å, =103.60(7)^o,Z=2,R _F=0.087 for 1187 intensities; -naphthyl-ammonium pentaiodide, triclinic,173-1,a=10.390(5),b=9.502(5),c=4.462(3) Å, =99.19(7), =90.40(7),=108.49(8)^o,Z=2,R _F=0.059 for 1319 intensities;N-methyl--picolinium heptaiodide, monoclinic,C2/c,a=19.315(7),b=12.714(5),c=8.442(4) Å, =107.26(7)^o,Z=4,R _F=0.065 for 1336 intensities). All three structures can be described as having channel inclusion features; the cations are contained in channels in polyiodide frameworks based on different arrangements of I₂ molecules and I ₃ ^– anions. This structural type is the converse of the more widespread kind where polyiodide anions are contained in an organic matrix (e.g., cyclodextrin polyiodides). Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82016 (30 pages).Part X of Crystal Structures of Polyiodide Salts and Complexes. For Part IX, see F. H. Herbstein, G. M. Reisner, and W. Schwotzer,Acta Crystallogr. C, accepted for publication, 1984