12 Mechanisms in erganic chemistry are exciting and well-studied (sNI, SN2, E1 a

Question

12 Mechanisms in erganic chemistry are exciting and well-studied (sNI, SN2, E1 and E2). We wil rate specifically look at the Elimination reactions (El E2 reactions) and relate their mechanism to their law. These elimination reactions are common reactions to eliminate an atom (leaving group) from a substrate and form an alkene (double bond in basic renction conditions. Generic Example: RC a CH H Base RCHz LG LG alkene Conjugate Acid leaving Group Substrate Leaving Group base of Base product Compound a write the rate law for the following overall reaction, using the specific alkene formation reaction and provided elementary step: CH3CH,Br Base cH -CHL 1-Base Br- slow This is called an E2 reaction. How does the name relate to the reaction rate law? b Now looking at the same alkene reaction, write the rate law using the newly provided elementary seps. Show all your work! slow fast This is called an E1 reaction. How does the name relate to the reaction rate law?

Explanation / Answer

a) rate law = k [CH3CH2Br] [base-]

it is E2 reaction because rate depends on both alkyl halide concentration and base concentration

order with respect to CH3CH2Br is 1 and order withrespect to Base - is 1.

total order = 1+1 =2

so it is E2 reaction

b) rate = k [(CH3)3C-Br]

here rate only depends on alkyl halide concentration .

so order with respect to alkyl halide = 1 . it is E1 reaction

note and key point for above answers: rate law or rate only depends on slowest step and species which are involved in slowest step.

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