Of isomerisation

Chandler D 1978 Statistical mechanics of isomerisation dynamics in liquids and the transition state approximation J. Chem. Phys. 68 2959-70... 

All varieties of phellandrene are somewhat unstable and are easily susceptible of isomerisation. 

Kinetics and mechanisms of isomerisation and racemisation processes of six coordinate chelate complexes. N. Serpone and D. G. Bickley, Prog. Inorg. Chem., 1972,17,391-566 (359). 

Llewellyn, Green, and Cowley isolated the Co-H complex [CoH(CO)3(IMes)] 26, a relatively stable complex under inert conditions [31], The authors examined the hydroformylation activity of 1-octene with Co-hydride complex 26. With 8 atm of syngas (H /CO) at 50°C for 17 h and 1 mol% 26, the conversion to aldehyde products was 47% with a l b of 0.78. However, 83% of the product was the internal aldehyde 2-methyl-octanal, indicating isomerisation competed with hydroformylation and the rate of isomerisation occurred faster than hydroformylation. 

Here it is found that the rate of loss of optical activity and the rate of isomerisation are identical, and if the reaction is carried out in the presence of D20 (five moles per mole of substrate) no deuterium is incorporated into the product. The reaction is thus wholly intramolecular under these conditions—no carbanion is involved—and is believed to proceed via a bridged T.S. such as (30). With a number of substrates features of both inter- and intra-molecular pathways are observed, the relative proportions being dependent not only on the substrate, but to a considerable extent on the base and solvent employed also. 

As expected for a tricyano compound, it is highly endothermic (AH°j (s) +348.1 kJ/mol, 3.78 kJ/g), so its stability seems dubious [1]. However, because of isomerisation to the acidic dicyano-enimine (NC)2C=C=NH, it is considerably stabilised and the silver and sodium salts surprisingly are described as stable [2],... 

This, and the corresponding 5-chloro and 5-methoxy derivatives, tend to explode during vacuum distillation, and minimal distillation pressures and temperatures are recommended. This instability, (which was not noted for the homologues in which the hydrogen atom of the secondary amino group was replaced by alkyl) may be connected with the possibilty of isomerisation to the ac7-nitro iminoquinone internal salt species. 

Figure 23 Monitoring of isomerisation of allyl end groups of PPG to isopropenyl functionality over time by means of h NMR spectroscopy (a) 0 h, (b) 89 h and (c) 594 h. Reproduced from Ref. [56] with permission of John Wiley Sons, Inc.

Bartell and coworkers investigated the structures of a series of noncyclic alkanes by means of gas electron diffraction (14, 44, 45) and invoked for the interpretation of their results a simple force field which contained to a high extent vibrational spectroscopic constants of Snyder and Schachtschneider. This force field reproduces bond lengths and bond angles of acyclic hydrocarbons well, energies of isomerisation satisfactorily. As an example, Fig. 8 shows geometry parameters of tri-t-butylmethane as observed by electron diffraction and calculated with this force field (14). 

The method of catalyst immobilisation appeared to affect its performance in catalysis. Catalyst obtained by method II showed a low selectivity in the hydroformylation of 1-octene (l b aldehyde ratio was even lower than 2) at a very high rate and high yields of isomerised alkenes (Table 3.2, entry 2), whereas procedure IV resulted in a catalyst that was highly selective for the linear aldehyde (with a l b ratio of 37) (entry 5). In accordance with examples from literature it is likely that procedure II gave rise to the ionic bonding of ligand-free rhodium cations on the slightly acidic silica surface [29],... 

The lack of isomerisation indicates that a non-ionic process is involved. The reaction does not continue to give a polymerisation of ethylene, because in contrast to the tertiary C-Cl bond which is broken, the primary C-Cl bond which is formed is too strong to be activated sufficiently by the A1C13. For the polymerisations involving an organic (monomer) halide and a metal halide, such as ZnBr2, it seems reasonable to represent the insertion also as occurring via a 6-membered cyclic transition state (II) ... 

Criticisms of Claims in the Field of Isomerisation Polymerisation, Part I. Polymerisation of p-Methylstyrene, J.P. Kennedy, P.L. Magagnini, and P.H. 

When the cyclopropane ring of this interesting reaction product is broken as a result of isomerisation two substances may he formed ... 

The reaction conditions chosen for the in situ IR studies are often much milder (25-100 °C, 100 bar) than the process conditions (140 °C, 250 bar), which may not affect the equilibria, as the higher pressure compensates for the higher temperature. The relative rate, however, of isomerisation of 1-alkenes may increase dramatically between room temperature and 140 °C. 

At present the Wacker reaction should be regarded as a relatively slow process, with only a few hundred turnovers per hour at elevated temperatures and pressures. For internal alkenes the rate is one or two orders of magnitude lower and the reaction affords mixtures of products due to isomerisation. In the absence of isomerisation, the product of the Wacker oxidation of a 1-alkene is a... 

Several cases of isomerisation have been noted on reaction of olefinic phosphines with transition metals. The ligand ap reacts with (norbom-adiene)M(CO)4 (M = Cr, Mo, W) to give initially (cts-pp)M(CO)4. This may be followed by a slow equilibration to give a mixture of (cis-pp)M-(CO)4 and (fraMS-pp)M(C0)4. This ligand has not yet been found to isomerise with other transition metals. 

Table II. Ion Association Constants and First-Ordor Rato Constants for Chloride Exchange of Isomerisation of cis- and trans-[Co en2 Cl2]+...

Rates of isomerisation may be calculated from the variation of the product distributions with time either directly or as the ratio of the rate constants for isomerisation and hydrogenation [123,125]. The direct method, based upon that originally described by Twigg [121] for double bond migration assumes that the but-l-ene and but-2-enes have similar... 

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