Destroyer ochem # 71

[mmorris86]

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Can someone explain to me what happens in the 3rd reaction when 1,2 dibromopropane goes to methylacetylene?? 😕 At best could someone explain/show me the mechanism, at worst could someone give me a clue😛

This is my first post on SDN so be kind... Thanks!!

 

[joonkimdds]

renew your destroyer 🙂

 

[cooki3monster]

It occurs via elimination, E1 or E2. I can't tell which one it is because i don't have DAT destroyer but if the solvent is protic, then it should be E1. If it's a basic nucleophile with a negative charge, then it would be E2. Elimination occurs twice to get the triple bond.

 

[PooyaH]

NaNH2 is a strong base, so it pulls off the Br's and additional hydrogens from the adjacent carbons to make a triple bond!

 

[mmorris86]

Ok I should have been more clear about what I didnt understand, but it was late and i had studied for like 8 hrs... no brain cells left

How can both the Bromines get eliminated? because once you eliminate the first, you will have an alkene and I always thought Elimination reactions were only possible on sp3 carbons. so how do you eliminate the 2nd bromine to go from alkene > alkyne?

 

[PooyaH]

You should notice that there are 3 NaNH2's used in the reaction. It's strong enough to pull off the second Br from the alkene. However, these things are good to know for your own knowledge and understanding, but it's a waste of time for the DAT. For the DAT, just know when you have NaNH2 reacting with an alkane, you should expect to get an alkyne!

 

[mmorris86]

Thanks I appreciate it, I am one of those weird guys who can't memorize orgo... i did really well when i took the class because i actually knew most of the mechanisms but that was 2 years ago and now i have forgotten so much of it 🙁

I've read on here that the DAT isnt as complex as destroyer, so hopefully thats true. I've been having a real hard time with the sugar stuff on destroyer like # 78 and #89 because we never went over that stuff in my orgo class.

 

[PooyaH]

Those questions are more of biochem than ochem. Just memorize them! Ochem on the DAT is very simple only if you pay attention to every detail! You can make a lot of loopholes with ochem questions that could distract you! I think I went over my ochm section in 10 min. lol so overall it's not that bad