Cyano radicals

Nobes, Pople, Radotn, Handy and Knowles have studied the convergence of the Moller-Plesset orders in some detail. They computed the energies of hydrogen cyanide, cyanide anion and cyano radical through order 24 as well as at the full Configuration Interaction level. Here are some of their results ... 

While in the case of the cyano radical based salts, most of the observed structures present a type I structural arrangement, in the case of the metal bisdichalcogenate-based... 

In his first experiment (1987) Zewail studied the unimolecular disintegration of iodine cyanide into iodine atom and cyano radical ICN I + CN. They managed to observe a transition state corresponding to the I-C bond breaking. The whole reaction was over in 200 fs. 

Isomer Distributions for Cyanations Initiated via Cation Radicals and Cyano Radicals 2... 

Anodic cyanation has been shown to be a direct process by electrochemical methods in conjunction with the analysis of products from cpe experiments (nos. 11 and 34, Table 8). In addition, cyano radicals can be generated in homogeneous solution, and a comparison of processes initiated by radical cation and cyano radical initiated processes reveals the indiscriminate nature of the latter towards aromatic substrates (cf. also Williams, 1960). This is in contrast to the electrophilic nature of the radical cation process. 

FIGURE 11.10 Products formed in the reactions of ethynyl and cyano radicals with unsaturated hydrocarbon molecules under single collision conditions. The reaction of ethynyl radicals with benzene is currently being studied in our laboratory. 

Miura et al. built on Ryu s previous work to achieve four-component radical cascades leading to diketones (Scheme 63) [174]. This outstanding result relies on initial carbonylation of alkyl radicals to form acyl radicals, such as 196. The nucleophilicity of acyl radicals allowed them to react with electron-deficient olefins to form ct-cyano radicals (197), whose phihcity is now reversed. Thus, they were able to add onto stannyl enolates and led to ketyl radicals such as 198. Those latter radicals underwent / -elimination of trib-utylstannyl radicals. This key elimination regenerated the mediator for the initial dehalogenation. This very fine tuning of the radical reactivities is the key element that makes the whole process work. 

The situation in which the supporting electrolyte and/or the solvent is oxidized at a lower potential than the organic substrate is frequently encountered. Anodic methoxylation and cyanation are two typical cases for which homolytic processes involving methoxy and cyano radicals, respectively, have been invoked [125,126]. However, it can be shown that in cyanation [127-129] and at least some cases of methoxylation [130], one must work at an anode potential around or higher than the half-wave potential of the organic substrate in order to get any substitution product. Similar mechanism problems are apparent for the side-chain acetoxylation of alkylaromatic compounds in Ac0H-Me4NN03 [131,132]. 

Anodic cyanation of alkoxylated biphenyls and other aromatic ethers is a limited but preparatively useful method for the formation of C-C bonds under mild conditions, as shown in Eq. (47) [103]. Mechanistic studies [104,105] supported a mechanism involving nucleophilic attack by cyanide ion on the aromatic radical cation rather than attack on the neutral aromatic nucleus by anodically generated cyano radicals, as had been proposed earlier [106]. 

The reaction was initially believed to be a homolytic substitution reaction by ano-dically generated cyano radicals [214]. However, while significant oxidation of CN takes place at a potential as low as 0.5 V versus SCE, the cyanation process will occur only in the region around or above "1/2 of the substrate. This strongly implies a direct mechanism [215,219,220] analogous to that for acetoxylation. 

Since, further, the attack on a group of atoms may occur sometimes from the one side and sometimes from the other, a constituent part will at times have to be taken as belonging to the radical, while in other reactions it will appear to belong to the type. Even the very simplest compounds show such varying behavior, and in the most obvious manner. All cyano compounds, for instance, can in certain reactions be considered as compounds of the cyano radical N in other reactions (those in which nitrogen is offered the opportunity of forming ammonia) they appear as amide-like compounds, i.e. substances belonging to the ammonia type in which H is replaced by some residue, e.g. ... 

In the last decades there has been much interest in the reaction of the cyano radicals, CN(x2e+), with a variety of molecules, mainly because of their implication in combustion chemistry [1]. For this reason extensive studies of CN reactions with simple molecules of relevance in combustion, amongst which are simple unsaturated hydrocarbons, were performed [2 5]. More recently, a renewed interest in the reactions of CN radicals with simple unsaturated hydrocarbons has arisen because of their alleged role in some... 

After entering the collision chamber, the cyano radical beam collides with the molecules of the second pulsed beam with a collision angle of 90°. The unsaturated hydrocarbon beams were produced by expanding the pure gas or vapor at room temperature through a pulsed valve. For the experiments described here the typical collision energies are in the range 13.0—35.0kJ/mol. The reaction products are detected at different laboratory angles by the QMS which is preceded by an electron impact ionizer the velocity distributions... 

In the previous section, we have seen how the presence of a -CH3 group has a strong influence on the chemistry of CN addition to a triple acetylenic bond. In this section we further explore such an effect by moving to the fully CH3-substituted species, dimethylacetylene. Also, in this case, we expect a similar reactive approach with the cyano radical attacking the n-orbital of the dimethylacetylene molecule. The possible reaction routes are (Figure 14.10)... 

R.I.K is indebted to the Deutsche Forschungsgemeinschaft (DFG) for a Habilitation fellowship (IICl-Kal081/3-1) and D. Gerlich (University Chemnitz, Germany) for support N.B. thanks the Institute of Atomic and Molecular Sciences (lAMS), Taiwan, for a visiting fellowship (January-March-1999) and the Italian Space Agency (ASI) for partial support. The experimental work of the cyano radical reactions was further supported by Academia Sinica (November 1998 to July 1999). Both authors thank... 

Balucani, N. Asvany, O. Chang, A.H.H. Lin, S.H. Lee, Y.T. Kaiser, R.L Bettinger, H.F. Schleyer, P.v.R. Schaefer III, H.F. Crossed beam reaction of cyano radicals with hydrocarbon molecules 1 chemical dynamics of cyano-benzene (CgHsCN X AJ and perdeutero cyanobenzene (CgDsCN X Aj formation from reaction of CN(X S ) with benzene, CgHe (X Aig) and dg-benzene, CgDg (X Aig). J. Chem. Phys. 1999, 111, 7457-7471. 

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