Question

what is SN1 mechanism ? expalin it in cobalt (lll) octahedral complex s​

Answer 1

The SN1 reaction is a substitution reaction in organic chemistry. "SN" stands for "nucleophilic substitution", and the "1" says that the rate-determining step is unimolecular.[1][2] Thus, the rate equation is often shown as having first-order dependence on electrophile and zero-order dependence on nucleophile. This relationship holds for situations where the amount of nucleophile is much greater than that of the carbocation intermediate. Instead, the rate equation may be more accurately described using steady-state kinetics. The reaction involves a carbocation intermediate and is commonly seen in reactions of secondary or tertiary alkyl halides under strongly basic conditions or, under strongly acidic conditions, with secondary or tertiary alcohols. With primary and secondary alkyl halides, the alternative SN2 reaction occurs. In inorganic chemistry, the SN1 reaction is often known as the dissociative mechanism. This dissociation pathway is well-described by the cis effect. A reaction mechanism was first proposed by Christopher Ingold et al. in 1940.[3] This reaction does not depend much on the strength of the nucleophile unlike the SN2 mechanism. This type of mechanism involves two steps. The first step is the reversible ionization of Alkyl halide in the presence of aqueous acetone or an aqueous ethyl alcohol. This step provides a carbocation as an intermediate.

Rates of acid hydrolysis have been measured for three series of complex ions of the types cis-[CoA4Cl2]+, trans-[CoA4Cl2]+ and [CoA5Cl]+2, in which the extent of chelation by the A groups is varied. It was found that in general the rate of acid hydrolysis decreased with increase in chelation. Arguments are presented to show that these results can be accounted for either on the basis of a dissociation (SN1) or a displacement (SN2) mechanism. It is, however, suggested that the observations are somewhat more consistent with an SN1 process.