Why would this reaction favor E2 over SN2??
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E2/SN2 question...
- Thread starter FurmanGal
- Start date
Why would this reaction favor E2 over SN2??
Thanks! I understand that it is a strong base, but isn't NaOH also considered to be a strong nucleophile? And i thought since it was on a primary carbon, it would typically proceed SN2 over E2. But I guess this isn't always true...
Thanks! I understand that it is a strong base, but isn't NaOH also considered to be a strong nucleophile? And i thought since it was on a primary carbon, it would typically proceed SN2 over E2. But I guess this isn't always true...
Correct. I don't know where you got this problem from but I suggest you find a new source for practice. This rxn undergoes SN2 major 75% to the E2 minor 25%.
The main reasons that E2 IS NOT favored. 1) not a tertiary halide, 2) doesn't form a highly substituted double bond, 3) doesn't form a conjugated alkene. Product is primary alcohol via SN2.
Whew, thanks rnbaxter! That's what I thought... I was getting so worried that my test is in less than 2 weeks and im still predicting simple reactions wrong. I just started using the Ohio State website that several people on SDN have recommended for extra practice (http://legacyweb.chemistry.ohio-state.edu/flashcards/) when I came across that reaction under the alkanes. Butttt good advice. i think i might just stick with my own destroyer roadmap flashcards from now on... 🙂
Whew, thanks rnbaxter! That's what I thought... I was getting so worried that my test is in less than 2 weeks and im still predicting simple reactions wrong. I just started using the Ohio State website that several people on SDN have recommended for extra practice (http://legacyweb.chemistry.ohio-state.edu/flashcards/) when I came across that reaction under the alkanes. Butttt good advice. i think i might just stick with my own destroyer roadmap flashcards from now on... 🙂
Glad to help 🙂 My DATs on Tuesday, just chillin and waitin for the hours to roll by can't wait to celebrate it bein over so I can have a little bit of summer before school starts back up again lol
SN2 refers to substitution nucleophilic bimolecular.
ie. something leaves and it is replaced
But what you have in the reaction above is not substitution but elimination (E2).
ie. Br is a good leaving group, it left but was not replaced/nor substituted and also one H was lost (neither substituted) from the adjacent carbon leading to the formation of a double bond thus and elimination reaction.
Just a caution for you. you dont have to take it. thanks.
ie. something leaves and it is replaced
But what you have in the reaction above is not substitution but elimination (E2).
ie. Br is a good leaving group, it left but was not replaced/nor substituted and also one H was lost (neither substituted) from the adjacent carbon leading to the formation of a double bond thus and elimination reaction.
Just a caution for you. you dont have to take it. thanks.
Glad to help 🙂 My DATs on Tuesday, just chillin and waitin for the hours to roll by can't wait to celebrate it bein over so I can have a little bit of summer before school starts back up again lol
Ahh GOOD LUCK tomorrow!!!!!! 🙂 . Looking forward to the breakdown. Mine is a week from Wednesday and I will have a total of 3 sweeeeet days to enjoy my summer until school starts back.... ugh lol
SN2 refers to substitution nucleophilic bimolecular.
ie. something leaves and it is replaced
But what you have in the reaction above is not substitution but elimination (E2).
ie. Br is a good leaving group, it left but was not replaced/nor substituted and also one H was lost (neither substituted) from the adjacent carbon leading to the formation of a double bond thus and elimination reaction.
Just a caution for you. you dont have to take it. thanks.
Hey. I realize that the reaction above is an E2 reaction and not an SN2 reaction. Are you trying to say that it should rightfully proceed E2 favorably? If so, my question is WHY did it get eliminated and not substituted?
Hey. I realize that the reaction above is an E2 reaction and not an SN2 reaction. Are you trying to say that it should rightfully proceed E2 favorably? If so, my question is WHY did it get eliminated and not substituted?
So this is a dehydrohalogenation reaction and it may very well occur with a basic solvent reagent. The fact the Hydrogen and Bromine got eliminated and not replaced is the reason why it is E2 favored and not substituted.
Rate = k[alkyl halide][base] = E2
for easy understanding draw out the complete structure of Bromoethane with all the hydrogen.
From my knowledge I do not know of SN2 reactions resulting in the formation of alkenes from alkanes.
This is one of the methods for the synthesis of alkenes
More so SN2 is best methyl>1>2 least substrate but with E2 it does not matter so much which substrate though by preference it will go the opposite direction.
Please read up dehydrohalogenation reactions for alkene formation.
Also note >>>>>>>>>>> Increasing rate of dehydrohalogenation.
RF<RCL<RBr<RI
Typing is not my thing but I hope I made sense
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This is confusing as well. I thought the rxn would've have been a SN2 rxn.
Typically, for primary/methyl halides, if you have a strong base and strong nucleophile (ie. RO-), then yes it would undergo SN2.
For secondary or tertiary halides, with a strong base and nucleophile, you would undergo E2.
However, it's typically to make both products, just one product will be a major product.
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My guess would be that it would be SN2? Could someone clarify this?
Typically, for primary/methyl halides, if you have a strong base and strong nucleophile (ie. RO-), then yes it would undergo SN2.
For secondary or tertiary halides, with a strong base and nucleophile, you would undergo E2.
However, it's typically to make both products, just one product will be a major product.
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My guess would be that it would be SN2? Could someone clarify this?
