Isocyanides isomerization

Rabinovitch and co-workers found that the Lindemann mechanism is adequate for modeling the pressure dependence of bimolecular region unimolecular rate constants for extracting collision efficiencies for the methyl isocyanide isomerization [122]. For the conformer conversion of molecule A at constant temperature, it can be written as,... 

Theoretical description of the hydrogen cyanide-hydrogen isocyanide and lithium cyanide-lithium isocyanide isomerization using the FSGO method. ... 

Figure 1. Reaction energy profile for cyanide-isocyanide isomerization reaction. NLSD [SDCI].

From the results of classical trajectory calculations intrinsic non-RRKM behavior has been predicted for ethane dissociation, ethyl radical dissociation,and methyl isocyanide isomerization. These predictions are supported by classical trajectory calculations for model H-C-C -> H + C=C dissociation. To generalize, classical trajectory calculations have predicted intrinsic non-RRKM behavior for molecules with isolated high frequency modes [e.g, CH3NC, clusters like Li (H20)j, and van der Waals molecules], molecules like acetylene with linear geometries for which bending and stretching motions are nearly separable, and molecules with tight activated complexes. 

Though unimolecular fall-off curves are important historically, their general insensitivity to intramolecular dynamics suggests that other types of experiments are more useful for detecting intrinsic non-RRKM behavior. Such an experiment is the one by Reddy and Berry on allyl isocyanide isomerization ... 

Here one-photon absorption is used to prepare allyl isocyanide with 5, 6, and 7 quanta in the terminal olefinic (H2C=), nonterminal ole-finic (=CH-), or methylene (-CH2 ) CH stretches. Because of their different frequencies each of these CH stretches can be excited selectively with very little spectral impurity. For a particular overtone the methylene CH stretch contains the least energy and the terminal olefinic CH stretch the most. Unimolecular rate constants were measured by Stern-Vollmer plots, and were found not to agree with RRKM predictions. Though the terminal olefinic CH stretch is most excited for a particular overtone, excitation at this site gives a smaller unimolecular rate constant than does excitation at the nonterminal olefinic CH stretch. This result unambiguously characterizes allyl isocyanide isomerization as intrinsically non-RRKM. 

The direct combination of selenium and acetylene provides the most convenient source of selenophene (76JHC1319). Lesser amounts of many other compounds are formed concurrently and include 2- and 3-alkylselenophenes, benzo[6]selenophene and isomeric selenoloselenophenes (76CS(10)159). The commercial availability of thiophene makes comparable reactions of little interest for the obtention of the parent heterocycle in the laboratory. However, the reaction of substituted acetylenes with morpholinyl disulfide is of some synthetic value. The process, which appears to entail the initial formation of thionitroxyl radicals, converts phenylacetylene into a 3 1 mixture of 2,4- and 2,5-diphenylthiophene, methyl propiolate into dimethyl thiophene-2,5-dicarboxylate, and ethyl phenylpropiolate into diethyl 3,4-diphenylthiophene-2,5-dicarboxylate (Scheme 83a) (77TL3413). Dimethyl thiophene-2,4-dicarboxylate is obtained from methyl propiolate by treatment with dimethyl sulfoxide and thionyl chloride (Scheme 83b) (66CB1558). The rhodium carbonyl catalyzed carbonylation of alkynes in alcohols provides 5-alkoxy-2(5//)-furanones (Scheme 83c) (81CL993). The inclusion of ethylene provides 5-ethyl-2(5//)-furanones instead (82NKK242). The nickel acetate catalyzed addition of r-butyl isocyanide to alkynes provides access to 2-aminopyrroles (Scheme 83d) (70S593). 

Diaziridinone (167) was also obtained in attempted syntheses of oxaziridinimine (282) from either di-t-butylcarbodiimide and peracid, or nitrosoisobutane and t-butyl isocyanide, probably by valence isomerization of the transient (282) (70JOC2813). 

Hydride complexes NMR spectra Hydroxide Infrared spectra Isocyanide complexes Isomerism in complexes... 

Our interest in thermally activated unimolecular reactions is in the change of kuni with pressure from the high to the zero pressure limit, and in the pressure dependence of the isotope effect over that range. One particularly interesting study carried out by Rabinovitch and Schneider (reading list) focused on the isomerization of methyl isocyanide, CH3NC, to methyl cyanide, CH3CN... 

Fig. 14.1 The pressure dependence of the 2°-a-D isotope effect, kn/kn, on the bimolecular isomerization of methyl isocyanide ...

Schneider, F.W. and Rabinovitch, B. S., The unimolecular isomerization of methyl-d3 isocyanide. Statistical-weight inverse secondary intermolecular kinetic isotope effects in nonequilibrium thermal systems. J. Am. Chem. Soc. 85, 2365 (1963). 

Bradford, A.M., Kristof, E., Rashidi, M., Yang, D.S., Payne, N.C. and Puddephatt, R.J. (1994) Isocyanide and diisocyanide complexes of a triplatinum cluster fluxionality, isomerism, structure, and bonding. Inorg. Chem., 33, 2355. 

George and co-workershave investigated the reaction of cyclohexyl isocyanide (185) with DMAD and have shown that a major constituent of the product mixture is the 2 3 adduct (186) formed through a [6 -i- 4] addition of the initially formed intermediate (182) with the dipolar species (181, R = cyclohexyl). Thermal isomerization of 186 in refluxing xylene results in an isomeric spiro compound (187), whereas at higher temperatures, other valence isomers of 186 are formed (Scheme 29). - Winterfeldt had earlier isolated a 1 2 adduct (188) from the reaction of cyclohexyl isocyanide with DMAD. The reaction of some alkyl and aryl isocyanides with acetylenic esters in protic solvents, such as methanol, has been reported to give open-chain adducts with the incorporation of one or two solvent molecules. 

Lever has successfully predicted Mn"/ potentials of 24 Mn-carbonyl complexes containing halide, pseudohalide, isonitrile, and phosphine co-ligands, with additivity parameters derived from the potentials of Ru "/" couples [39]. An important consideration for heteroleptic complexes is the influence of isomerism on redox thermodynamics. For Mn(CO) (CNR)6- complexes, with n = 2 or 3, the Mn"/ potentials for cis/trans and fac/mer pairs differ by as much as 0.2 V [40]. The effect arises from the different a-donor and 7r-acceptor abilities of carbonyl (CO) and isocyanide and their influence on the energy of the highest energy occupied molecular orbital (HOMO). 

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