Exploring potential energy surfaces for chemical reactions: an overview of some practical methods

Potential energy surfaces form a central concept in the application of electronic structure methods to the study of molecular structures, properties, and reactivities. Recent advances in tools for exploring potential energy surfaces are surveyed. Methods for geometry optimization of equilibrium structures, searching for transition states, following reaction paths and ab initio molecular dynamics are discussed. For geometry optimization, topics include methods for large molecules, QM/MM calculations, and simultaneous optimization of the wave function and the geometry. Path optimization methods and dynamics based techniques for transition state searching and reaction path following are outlined. Developments in the calculation of ab initio classical trajectories in the Born-Oppenheimer and Car-Parrinello approaches are described.     

Synthesis,Characterization and Crystal Structures of new Coordination Polymers of Cerium(III) and Samarium(III) Containing 2,6‐Pyridinedicarboxylic Acid

The reaction of 2,6‐pyridinedicarboxylic acid ( 1 , LH₂) with CeCl₃·7H₂O and Sm(NO₃)₃·6H₂O in the presence of triethylamine led to the coordination polymer complexes [M(L)(LH)(H₂O)₂]·4H₂O [M = Ce ( 2 ) and Sm ( 3 )]. Both complexes were characterized by elemental analyses, IR spectroscopy and the crystal structures of 2 and 3 . Crystal data for 2 at ?80 °C: monoclinic, space group P2₁/c, a = 1404.6(1), b = 1122.1(1), c = 1296.1(1) pm, β = 102.09(1)°, Z = 4, R₁ = 0.0217 and for 3 at ?80 °C: monoclinic, space group P2₁/c, a = 1395.1(1), b = 1120.1(1), c = 1282.8(1) pm, β = 102.71(1)°, Z = 4, R₁ = 0.019.     

Chemical Applications of Raman Spectroscopy

Raman spectorscopy is—like infrared spectroscopy—a method for the study of vibrations of molecules and crystals. The two methods are complementary: if a vibration results in a change of the polarizability of a molecule, it is Raman active; if a change in the molecular dipole moment results, it is infrared active Vibrations of nonpolar groups and totally symmetrical vibrations of molecules are often only Raman active. IR and Raman spectra together give information about the symmetries and structures of molecules and crystals and about the properties of chemical bonds and intermolecular interactions. Until about 10 years ago Raman spectra could only be recorded on relatively large amounts of essentially colorless substances. After the advent of laser light sources the situation changed completely. The amount of sample substance required is now in the region of milli- and micrograms. Gases, liquids and solid samples, especially air-sensitive and reactive substances, single crystals, crystal needles and filaments as well as aqueous solutions can be readily investigated. The identification of molecules and the elucidation of molecular structures, biochemical analysis, and control of evnivornmental pollution are important aplications of Raman spectroscopy. Raman spectroscopy now constitutes an additional powerful tool in instrumental analysis     

2,6-diaza-4,8-dicyanosemibullvalene. A short lived intermediate?

Reductive dehalogenation of dichloride with magnesium affords the new stable diazacyclooctatetraene (1,5-diazocine) . There is strong evidence for the intermediate formation of a 2, 6-diaza-4,8 - dicyanosemibullvalene .     

Aromatisierung von cytclohexenon-derivaten über selenorganische zwischenstufen

Reaction of the hydroaromatic compounds ($\text{1a}$) and ($\text{3a}$) with lithium-diisopropylamide followed by phenylselenenyl chloride gives the selenides ($\text{1b}$) and ($\text{1c}$) resp. ($\text{3b}$), which form exclusively the phenols ($\text{4}$) resp. ($\text{6}$) after oxidation with 3-chloroperbenzoic acid in the presence of 3,5-dimethoxyaniline ($\text{7a}$).     

The Uracil C(5) Position as a Metal Binding Site: Solution and X-ray Crystal Structure Studies of Pt(II) and Hg(II) Compounds

1,3-Dimethyluracil (1,3-DimeU) reacts with trans-[(CH(3)NH(2))(2)Pt(H(2)O)(2)](+) to give trans-[(CH(3)NH(2))(2)Pt(1,3-DimeU-C5)(H(2)O)]X (X = NO(3)(-), 1a, ClO(4)(-), 1b) and subsequently with NaCl to give trans-(CH(3)NH(2))(2)Pt(1,3-DimeU-C5)Cl (2) or with NH(3) to yield trans-[(CH(3)NH(2))(2)Pt(1,3-DimeU-C5)(NH(3))]ClO(4) (3). In a similar way, (dien)Pt(II) forms [dienPt(1,3-DimeU-C5)](+) (4). Reactions leading to formation of 1 and 4 are slow, taking days. In contrast, Hg(CH(3)COO)(2) reacts fast with 1,3-DimeU to give (1,3-DimeU-C5)Hg(CH(3)COO) (5). Both 1-methyluracil (1-MeUH) and uridine (urdH) react with (dien)Pt(II) initially at N(3) and subsequently with either (dien)Pt(II) or Hg(CH(3)COO)(2) also at C(5) to give the diplatinated species 7 and 9 or the mixed PtHg complex 8. C(5) binding of either Pt(II) or Hg(II) is evident from coupling of uracil-H(6) with either (195)Pt or (199)Hg nuclei and (3)J values of 47-74 Hz (for Pt compounds) and 185-197 Hz (for Hg compounds). J values of Pt compounds are influenced both by the ligands trans to the uracil C(5) position and by the number of metal entities bound to a uracil ring. Both 2 and 5 were X-ray structurally characterized. 2: monoclinic system, space group P2(1)/c, a = 15.736(6) ?, b = 11.481(6) ?, c = 25.655 (10) ?, beta = 145.55(3) degrees, V = 2621.9(28) ?(3), Z = 4. 5: monoclinic system, space group P2(1)/c, a = 4.905(2) ?, b = 18.451(6) ?, c = 11.801(5) ?, beta = 94.47(3) degrees, V = 1064.77(72) ?(3), Z = 4.     

Struktur von S-9,10-Dimethyl-1,3,5,7-tetraarsa-2,4,6,8-tetraoxaadamantan und 9,10-Diethyl-1,3,5,7-tetraarsa-2,4,6,8-tetraoxaadamantan

Structure of S-9,10-Dimethyl-1,3,5,7-tetraarsa-2,4,6,8-tetraoxaadamantane and 9,10-Diethyl-1,3,5,7-tetraarsa-2,4,6,8-tetraoxaadamantane S-9,10-Dimethyl-1,3,5,7-tetraarsa-2,4,6,8-tetraoxaadamantane ( 1 ) and 9,10-diethyl-1,3,5,7-tetraarsa-2,4,6,8-tetraoxaadamantane ( 2 ) have been prepared by the reaction of propionic acid, propionic anhydride and butyric acid, butyric anhydride, respectively, with arsenic(III)-oxide. The crystals of 1 are rhombic, a = 6.902(4), b = 11.121(5), c = 13.988(8), space group P2₁2₁2₁. The crystals of 2 are monoclinic, a = 11.757(10), b = 11.255(10), c = 18.631 (18), β = 91.78(7), space group P2₁/n. The mean bond lengths and angles in 1 are AsO = 1.790 Å, AsC = 1.959 Å, OAsO = 100.60°, CAsO = 99.65°, AsOAs = 128.77°, AsCAs = 118.73°, and in 2 they are AsO = 1.780 Å, AsC = 1.978 Å, OAsO = 101.45°, CAsO = 99.55°, AsOAs = 129.64°, AsCAs = 117.72°.     

Delayed fluorescence S2 → S0 of azulene in isopentane,due to hetero-triplet—triplet annihilation of 3azulene* and 3fluoranthene*

The lowest triplet state of azulene, T₁(Az), can be populated efficiently by triplet energy transfer from the lowest triplet state of fluoranthene, T₁(F1). In isopentane at temperatures 120 K ? T ? 193 K a delayed fluorescence S₂(Az) → S₀(Az) is found, caused by hetero-triplet—triplet annihilation T₁(Az) + T₁(Fl) → S₂(Az) + S₀(F1).     

Der Stoffwechsel von Verbindungen mit Dreifachbindung. VI. Stoffwechselverhalten von Alkincarbonsäuren und Alkindicarbonsäuren

Metabolism of Acetylenic Monocarboxylic and Dicarboxylic Acids Feeding of acetylenic monoacids with chain length of 11 to 18 C-atoms to rats led to excretion of dicarboxylic acids with retained triple bonds. 10-Octadecynoic acid led to the formation of metabolites with even and odd number of C-atoms, suggesting in addition to established ω- and β-oxidation an α-oxidative pathway.