Important! Answer these questions before coming to lab. Write the answers in you
ID: 1050125 • Letter: I
Question
Important! Answer these questions before coming to lab. Write the answers in your notebook and on a sheet of paper to turn in at the start of lab. Predictions prior to the experiment: Predict the reactivity of the alkyl halides in the Table with Nal/action from most reactive to least reactive. Briefly explain your reasoning. Predict the reactivity of the alkyl halides in the Table with AgNO_3/ethanol from most reactive to least reactive. Briefly explain your reasoning.. Which compounds, if any, are there that you would expect to be unreactive under both sets of conditions? Briefly explain your reasoning.Explanation / Answer
The reaction of alky halides with sodium iodide in acetone is an SN2 reaction.
Here the iodide ion is the nucleophile. The order of reactivity is primary> secondary > tertiary.
SN2 reactions are favoured by very good nucleophile and polar aprotic solvent. Here I- is a very good nucleophile and acetone is a polar aprotic solvent.
The reaction of alky halides with AgNO3 in ethanol is by SN1 reaction.
In SN1 reaction the rate determining step involves the formation of carbocations and the reaction rate is governed by the stability of carbocations.
Thus a tertiary carbocation is more stable than secondary and secondary is more stable than a primary.
Here the order of reactivity in an SN1 reaction is tertiary > secondary >primary
Here Ag+ in protic solvent rapidly generates R+ and AgX and the subsequent reaction of R+ with solvent to yield the product
Bromobenzene is found to be unreactive under both conditions.
In the case of an SN2 reaction , the nucleophile must attack from behind the carbon which is hindered by the bulky ring. Since all the carbons in benzene ring have sp2 hybridised orbitals an SN1 recation cannot occur.