Ring Opening Of Cis Research Articles

Kinetics and mechanism of the acid-catalysed ring opening of cis[Co(en) 2-(β-alaO)] 2+

The preparation of cis-[Co(en) 2(β-alaO)]I 2 is described. Ring opening of the complex occurs in acidic solution. Kinetic studies establish that the reaction shows a first-order dependence on [H +] with rate = k H[Complex][H +]. Values of k H have been determined over a temperature range giving ΔH‡ = 59.9 kJ mol −1 and ΔS‡ 298 = -50 J K −1 mol −1. The solvent deuterium isotope effect k D, 2O /k H, 2O , for the ring opening process is 2.4, consistent with a mechanism involving a rapid pre-equilibrium protonation step followed by slow rate-determining ring opening. Mechanism involving concerted attack by H + and H 2O are excluded.

Effect of Conformation on Ring Opening of Cis and Trans Dimers of Acenaphthylene in the Triplet State. Direct Detection of Hydrocarbon Biradical, 1,1′-Biacenaphthene-2,2′-diyl

Abstract Triplet sensitized photodecomposition of cis and trans dimers of acenaphthylene (c-D and t-D) has been studied in benzene by means of a nanosecond laser flash photolysis. An aromatic hydrocarbon biradical, 1,1′-biacenaphthene-2,2′-diyl (1) was found as an intermediate for the decomposition of triplet t-D to acenaphthylene monomers. The rate of bond opening was directly measured to be 8.3×106 s−1 at 20 °C. The temperature dependence of the rate yields the frequency factor 2.8×107 s−1 and activation energy 3.1 kJ mol−1. The lifetime of 1 is 330 ns; this is insensitive to temperature changes (6–64 °C). Oxygen quenches 1 with the rate constant of 9×109 M−1 s−1 (1 M=1 mol dm−3). On the other hand, the triplet state of c-D did not show any evidence of the presence of 1 as an intermediate. The difference of ring opening mechanisms between the two isomers is interpreted in terms of different steric hindrances between two acenaphthene rings. The triplet-triplet (T-T) absorption spectra of both dimers resemble each other. No characteristic absorption due to intramolecular triplet excimer of naphthalene was observed even for c-D.

Photoisomérisation des quelques cyclohexadiènes et heptatriènes. Photocycloaddition des hexatriènes

AbstractPhotolytic ring opening of cis and trans‐1,5‐diphenyl‐6‐méthylcyclohexa‐1,3‐dienes yields a unique primary triene with a geometry determined by the cyclodiene preferred conformation in the ground state.Irradiation of 3 isomers of 1,5‐diphenylhepta‐1,3,5‐triene with a cis‐central double bond (Z, Z, E; E, Z, E and E, Z, Z) yields with a complete stereospecificity 3 bicyclo[3.1.0]hexenes (respectively endo‐Me‐endo‐Ph; endo‐Me‐exo‐Ph and exo‐Me‐exo‐Ph). Kinetic measurements have shown that these internal photocycloadditions are of the type [4πa + 2πa], which is forbidden by Woodward‐Hoffmann rules. In all of the three cases studied by us, orbital factors seem anyway to play a major role compared to steric constraints (an endo‐endo photoproduct is formed).A kinetic study of the relative cis‐trans photoisomerization rates of carbon double bonds of the eight isomers of 1,5‐diphenylhepta‐1,3,5‐triene has been performed.

ChemInform Abstract: DIRECTION OF RING‐OPENING OF CIS‐ AND TRANS‐2‐METHYLCYCLOPROPYLCARBINYL RADICALS

The ring-opening of cis- and trans-2-methyl-cyclopropylalkyl radicals to give secondary and primary alkyl radicals respectively is not dependent on the presense of an OH or OSnR3 substituent at the reaction centre, and any interpretation of this effect in terms of the polar nature of these groups is insufficient.

Direction of ring-opening of cis- and trans-2-methylcyclopropylcarbinyl radicals

The ring-opening of cis- and trans-2-methyl-cyclopropylalkyl radicals to give secondary and primary alkyl radicals respectively is not dependent on the presense of an OH or OSnR3 substituent at the reaction centre, and any interpretation of this effect in terms of the polar nature of these groups is insufficient.

Epoxide Studies. I. The Ring Opening of cis- and trans- N,N-Diethylphenylglycidamide

Epoxide Studies. I. The Ring Opening of cis- and trans- N,N-Diethylphenylglycidamide

Proximity Effects. XXXII. Ring Opening of cis- and trans-Cycloöctene Oxide in Alumina-catalyzed and Uncatalyzed Pyrolysis and in Reaction with Magnesium Bromide Etherate

<b>Proximity Effects. XXXII. Ring Opening of <b><i>cis</i></b>- and <b><i>trans</i></b>-Cycloöctene Oxide in Alumina-catalyzed and Uncatalyzed Pyrolysis and in Reaction with Magnesium Bromide Etherate</b>