Synthesis and crystal structure of 4,5-dibromo[2.1.1]triblattene

Reaction of 4-bromopentacyclo[7.3.0.0^2,7.0^3,11.0^6,10]dodec-11-ene (1) with Br₂—CCl₄ afforded 4,4,5-tribromopentacyclo[7.3.0.0^2,7.0^3,11.0^6,10]dodecane (2) in 89–94% yield. Subsequent treatment of 2 with KOt-Bu-t-BuOH resulted in competitive elimination of the elements of HBr and of Br₂ with concomitant formation of 4,5-dibromopentacyclo[7.3.0.0^2,7.0^3,11.0^6,10]dodec-11-ene (3, 76%) and 1 (17%), respectively. The structure of 3 was established unequivocally via application of X-ray crystallographic methods. Crystal data for 3: monoclinic, C2/c, a = 9.895(1), b = 9.0963(7), c = 12.471(1) Å, = 106.875(8)°, z = 4.     

Structure of a deaza dimer of 4-methyl-3H-1,2,4-triazole-3,5(4H)-dione

The title compound crystallizes in the monoclinic space group, P2₁/n; a = 9.0024(5), b = 5.8135(3), c = 15.2232(8) Å, = 91.153(4)° Z = 4; and R = 0.050 based on 853 observed, unique reflections. The structure consists of two fused five-membered triazole rings, oriented relative to each other at 152°.     

A Vastly Increased Chemical Variety of RNA Modifications Containing a Thioacetal Structure

Recently discovered new chemical entities in RNA modifications have involved surprising functional groups that enlarge the chemical space of RNA. Using LC‐MS, we found over 100 signals of RNA constituents that contained a ribose moiety in tRNAs from E. coli. Feeding experiments with variegated stable isotope labeled compounds identified 37 compounds that are new structures of RNA modifications. One structure was elucidated by deuterium exchange and high‐resolution mass spectrometry. The structure of msms²i⁶A (2‐methylthiomethylenethio‐N6‐isopentenyl‐adenosine) was confirmed by methione‐D3 feeding experiments and by synthesis of the nucleobase. The msms²i⁶A contains a thioacetal, shown in vitro to be biosynthetically derived from ms²i⁶A by the radical‐SAM enzyme MiaB. This enzyme performs thiomethylation, forming ms²i⁶A from i⁶A in a first turnover. The new thioacetal is formed by a second turnover. Along with the pool of 36 new modifications, this work describes a new layer of RNA modification chemistry.     

Triméthylsilylcycloalcanes: Corrélation structure-réactivité

A comparative study of the physicochemical data (IR, Raman, ¹H, ¹³C and ²⁹Si NMR) of four trimethylsilylcycloalkanes, ($\text{CH}{}_2\text{)}{}_{\mathrm{<mtext>n</mtext>}}\text{C}$HSiMe₃ ( n = 2- 5), allowed a good correlation between their structure and chemical reactivity to be established. The particular chemical behaviour of trimethylsilylcyclopropane, in this series, involves an interaction between the three-membered ring and silicon, in good agreement with a (p → d)π interaction. This study provides a lot of new data for these models and exhibits exemplarily the contribution of physico-chemistry in explaining and predicting the chemical reactivity of organic substrates.     

Finite element error bounds for a curve shrinking with prescribed normal contact to a fixed boundary

We approximate the evolution of a curve subject to motion bycurvature by linear finite elements. The curve evolves insidea given domain and meets orthogonally. We derive optimal boundsfor the error with respect to the L²- and H¹-norms and presentsome computed examples.     

Les systemes binaires fluorure de lithium-fluorure d'hydrogene et fluorure de sodium-fluorure d'hydrogene

Liquid-solid equilibria in the binary systems LiF-HF and NaF-HF were studied up to 400° by thermal analysis. On account of the properties of hydrogen fluoride, a special apparatus was built. Several compounds were observed: LiF · HF-NaF · HF; NaF · 2HF; NaF · 3HF and NaF · 4HF. The characteristic temperatures of the systems, and especially the peritectic decompositions of LiF · HF and NaF · HF were determined, and the bibliographic data were corrected.     

The molecular geometry of a heptacyclotetradecane from gas-phase electron diffraction

Electron diffraction established firmly the structure of a heptacyclo [6.6.0.0^2,6.0^3,13.0^4,11.0^5,9.0^10,14] tetradecane molecule in which two norbornane units are rotated 90° relative to each other and linked by four methine bridges. The longest bond is the ethano bridge (1.586 ± 0.004 Å, r_g) and the methine bridge is considerably shorter (1.528 ± 0.006 Å r_g) than the mean CC bond length of the norbornane unit (1.557 Å). The molecular structure is generally consistent with the geometry of its crystalline di-tert-butoxy derivative as well as with that of gaseous norbornane.     

Effect of the chemical nature and length of spacer arms on the covalent grafting of fluorinated molecular probes at the surface of poly(ethylene terephthalate) membrane

A series of fluorinated molecular probes were synthesized that are characterized by spacer arms of various lengths and polarities. Previous molecules ( 1 , 2a , 2b , 2c , 3a , 3b ) were covalently fixed on the surface of poly(ethylene terephthalate) (PET) membranes via activated hydroxyl chain endings. X‐ray photoelectron microscopic analysis of the grafted samples allowed us to quantify the PET surface reactivity; the results were within 40–50 pmol/cm² of fixed probes, independent of the length and hydrophilicity of the spacer arms. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 770–781, 2002; DOI 10.1002/pola.10156