CH3CH2CH2CH2OTs can easily undergo Sx2 reaction with NaBr, while CH3CH2CH2OH doe
ID: 872510 • Letter: C
Question
CH3CH2CH2CH2OTs can easily undergo Sx2 reaction with NaBr, while CH3CH2CH2OH does not react with NaBr. On the other hand, CH2CH2CH2OH reacts readlly with HBr via the SN2 mechanism. Please explain all of these observations in terms of the quality of leaving groups. Please use a series of chemical equations with appropriate reaction conditions to plan the synthesis of 2-methylpropene with 2-methylpropane as the starting material in a chemistry laboratory. You can use any necessary reactions/reagents. Please suggest an explanation for the observed order of SN1 reactivity of the following compoundsExplanation / Answer
Answering your first question:
a leaving group is a molecular fragment that departs with a pair of electrons in heterolytic bond cleavage. Leaving groups can be anions or neutral molecules, but in either case it is crucial that the leaving group be able to stabilize the additional electron density that results from bond heterolysis. Common anionic leaving groups are halidessuch as Cl?, Br?, and I?, and sulfonate esters such as tosylate (TsO?). Fluoride (F?) functions as a leaving group in the nerve-agent sarin gas. Common neutral molecule leaving groups are water and ammonia.
The physical manifestation of leaving group ability is the rate at which a reaction takes place. Good leaving groups give fast reactions. By transition state theory, this implies that reactions involving good leaving groups have low activation barriers leading to relatively stable transition states.
The requirement for a good leaving group is relaxed in conjugate base elimination reactions. These reactions include loss of a leaving group in the ? position of an enolate as well as the regeneration of a carbonyl group from the tetrahedral intermediate in nucleophilic acyl substitution. Under forcing conditions, even amides can be made to undergo basic hydrolysis, a process that involves the expulsion of an extremely poor leaving group, R2N?. Even more dramatic, decarboxylation of benzoate anions can occur by heating with copper or Cu2O, involving the loss of an aryl anion. This reaction is facilitated by the fact that the leaving group is most likely an arylcopper compound rather than the much more basic alkali metal salt.
And for all of these reasons, The Ots is a ver well leaving group (Good lewis acid) and the OH is not.