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Suwwzznvy Several nickel( 0) complexes are excellent substrates containing carbon-halogen bonds,l cnrboncatalysts for the formation of alkylene carbonates from carbon n-bonds,2 and strained o-bonds," there are few data alkylene oxides and carbon dioxide.describing similar catalysis with compounds containiiig carboli-ox ygen bonds. SOLUBLE low-valent transition metal complexes have beenWe report that a series of co-ordinatively unsaturated recognized as important agents for effecting stoicheiornetric zerovalcnt nickel coillplexes catalyse the formation of and catalytic traiisforniations of various organic sub-alliylene carbonates: from certain eposides and carbon strates. U'hile nunierous catalytic reactions have been dioxide. %lien epoxyethme and carbon dioxide are hc-ated reported involving transition-metal-activation of organic at 100" in benzene solution containing L,Si5 (I, = Ph,I'), t Current address, PCR, Inc., Gaiiiesville, Florida 32G01.$ All inorganic complexes were satisfactorily characterized by elemental analyses, inolecuIar wieght determinations, and i.r. and n.m.r. spectroscopy while the organic carboiiates gave mass, i.r., and n.m.r. spectra consistent with their structures.

By kinetic simulation, the significant features of the mechanism of the low‐temperature photo‐oxidation of hexafluoropropene were elucidated and the rate constants for the major elementary reactions of the intermediate fluorinated peroxy and alkoxy radicals were determined through a best‐fit procedure. Comparison with analogue reactions in non‐fluorinated systems showed a significant increase in reactivity for the self‐reaction and double bond addition by peroxy radicals and β‐scission by alkoxy radicals, which are discussed in terms of fluorine substituent effects.

The RNA component, uracil, is reviewed from structural, spectroscopic, synthetic, chemical reactivity, biochemical, and application viewpoints. This fascinating molecule undergoes a plethora of reactions at nine different sites; the specificity of these is considered in some detail. The review contains 189 literature citations.Uracil, a major component of nucleic acid, has aroused the interest of numerous experimentalists. The properties and reactions of this molecule gain significance when one considers their relationship to the chemical modification of biologically active nucleic acids and, consequently, living organisms. An understanding of this interplay simultaneously nourishes biomedical applications and instills the awareness of potential hazards. This report highlights the properties and chemistry of uracil with the intention of hopefully stimulating future applications. PropertiesUracil [2,4(lH,3H)-pyrimidinedione, C4H4N202], a white crystalline solid, melts with decomposition at 335-338 °C. This pyrimidine derivative is essentially insoluble in cold water (pH 7) and typical organic solvents. It dissolves in boiling water (ca. 2 g/100 mL) and dipolar aprotic solvents, e.g., Me2SO (1) (5.6 g/100 mL at 23 °C). Due to its amphoteric nature it is soluble in acids, i.e., 35% H2S04 (ca. 1.5 g/100 mL at 25 °C), CF3C02H (2), HF (3), and bases. With regard to its weakly basic properties uracil has been used as an indicator to extend the acidity function Ha (4) up to 17% by weight S03 in H2S04, As acidity increases, uracil first protonates at the more basic site (0 at C4), then doubly protonates (0 at C4 and C2). In basic solution uracil behaves as a weak dibasic (5) acid with ionization first at N3 (pKa = 9.7) and then at N4 (pKa = 14.2), The ability of nucleic acid bases, including uracil, to associate by hydrogen bonding ( 6) is essential to their role in biological evolution. StructureAfter considerable difficulty, a single crystal of uracil was obtained (twinning is prevalent) and analyzed (7) by X-ray crystallography. The space group is P24/a; there are four molecules in the unit cell which are essentially parallel and held together by NH-0 hydrogen bonds. The molecule is planar in the solid state with the two sets of C-C and C-0 bonds being of similar length and exists in its lactam form.

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