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In coordination chemistry, the S N 1cB (conjugate base) mechanism describes the pathway by which many metal amine complexes undergo substitution, that is, ligand exchange. . Typically, the reaction entails reaction of a polyamino metal halide with aqueous base to give the corresponding polyamine metal hydroxi
Finally, conjugate base refers to the formation of the carbanion intermediate, which is the conjugate base of the starting material. E1cB should be thought of as being on one end of a continuous spectrum, which includes the E1 mechanism at the opposite end and the E2 mechanism in the middle.
On the other hand, if a chemical is a weak acid its conjugate base will not necessarily be strong. Consider that ethanoate, the conjugate base of ethanoic acid, has a base splitting constant (Kb) of about 5.6 × 10 −10, making it a weak base. In order for a species to have a strong conjugate base it has to be a very weak acid, like water.
A conjugate base is formed when the acid is deprotonated by the base. In the image above, hydroxide acts as a base to deprotonate the carboxylic acid. The conjugate base is the carboxylate salt. In this case, hydroxide is a strong enough base to deprotonate the carboxylic acid because the conjugate base is more stable than the base because the ...
Studies show, however, that in the hydroxide deprotonates one NH 3 ligand to give the conjugate base of the starting complex, i.e., [Co(NH 3) 4 (NH 2)Cl] +. In this monocation, the chloride spontaneously dissociates from this conjugate base of the starting complex. This pathway is called the Sn1CB mechanism.
Studies show, however, that the hydroxide deprotonates one NH 3 ligand to give the conjugate base of the starting complex, i.e., [Co(NH 3) 4 (NH 2)Cl] +. In this monovalent cation, the chloride spontaneously dissociates. This pathway is called the S N 1cB mechanism.
A variety of amines and nitrogen heterocycles are useful bases of moderate strength (pK a of conjugate acid around 10-13) . N,N-Diisopropylethylamine (DIPEA, also called Hünig's Base [1]), pK a = 10.75
The two main mechanisms were the S N 1 reaction and the S N 2 reaction, where S stands for substitution, N stands for nucleophilic, and the number represents the kinetic order of the reaction. [ 4 ] In the S N 2 reaction, the addition of the nucleophile and the elimination of leaving group take place simultaneously (i.e. a concerted reaction ).