Nitrile group, thermodynamic

For a cis alkene to be formed the reaction would have to proceed through a czs-a,p-disubstituted metallacyclobutane intermediate (cis isomer of 10). Although it was unclear why there was a preference for forming a cis metallacycle, which leads to the thermodynamically less stable product, it was probably related to the small size or the electron-withdrawing properties of the nitrile group. 

Acrylonitrile (C3H3N, mol wt = 53.064) is an unsaturated molecule having a carbon-carbon double bond conjugated with a nitrile group. It is a polar molecule because of the presence of the nitrogen heteroatom. Tables 1 and 2 list some physical properties and thermodynamic information, respectively, for acrylonitrile. 

Dithiane anions undergo intramolecular conjugate addition to die a,/ -unsaturated nitrile moiety in (150) to produce indolizidine and quinolizidine (151), in which the nitrile group exhibits a strong, thermodynamic preference for die axial orientation.108... 

The acetone cyanohydrin is employed as a solvent this means it is present in great excess. Under thermodynamic control this reaction preferentially leads to the formation of a cyanohydrin with an axial nitrile group and an equatorial OH group, since a nitrile group is smaller than an OH group. 

Pentenenitrile is first rapidly isomerized by the nickel catalyst to 4-pentenenit-rile. Addition of hydrogen cyanide then affords adiponitrile as the major product. This is fortunate, as the unwanted conjugated 2-pentenenitrile is thermodynamically more stable than either the 3- or the 4-isomer. The favourable initial course of the isomerization is thought to be controlled by the formation of a cyclic intermediate or transition state in which the nitrile group coordinates to nickel. 

Whereas additions of carbon radicals to alkene moieties are the best characterized homolytic additions, carbon radicals are known to add to a wide range of unsaturated systems. These include polyenes, alkynes, arenes, heteroarenes, carbon monoxide,isonitriles, °° ° nitriles, ° imines and derivatives, ° ° aldehydes,nitrones, and thiones. ° Many of these reactions, such as addition of an alkyl radical to a carbonyl group, ° are thermodynamically unfavorable and readily reversible, and they form the basis of composite group-transfer reactions discussed below. 

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