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hard exam questoin amino acids

why does the N on ammino acid have 3 CH3 and not 4 ? isn't it supposed to make a quaternary ammonium salt with excess haloalkane, im so confused
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usernamenew
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Original post by usernamenew
why does the N on ammino acid SERENE have 3 CH3 and not 4 ? isn't it supposed to make a quaternary ammonium salt with excess haloalkane, im so confused


serene is the one theyre asking for, in the answer the serene has a positive N and 3CH3 gorups attached
(edited 5 years ago)
aqa.PNG15.8KB
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usernamenew
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Original post by BobbJo
post actual question? what is it reacting with


Draw the structure of the species formed when serine reacts with an excess of bromomethane.
thought this would be a easy gcse bio question about protein and i could help for once :cry:
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Original post by BobbJo
you'll get RN+(CH3)3


yeah but why? thats my question, i dont get why theres not 4 alkyl groups around the N
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Original post by I'mComingOxford
thought this would be a easy gcse bio question about protein and i could help for once :cry:


sorry for the misleading title!
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Original post by BobbJo
I write serine as RNH2

1st substititution
1 lone pair on N attacks delta positive carbon on bromomethane
you get (CH3)RN+H2
RNH2 accepts one of the H on (CH3)RN+H2, electrons from the N-H bond go to the N and neutralise positive charge
you get (CH3)RNH

2nd substitution
1 lone pair on N attacks delta positive carbon on bromomethane
you get (CH3)2RN+H

RNH2 accepts one of the H on (CH3)2RN+H, electrons from the N-H bond go to the N and neutralise positive charge
you get RN(CH3)2


3rd substitution
1 lone pair on N attacks delta positive carbon on bromomethane
you get RN+(CH3)3

RNH2 cannot accept any more H. So reaction stops here. You actually only get a tertiary ammonium salt

thank u, so is the same idea used if another amino acid was used, will amino acids always form only tertiary ammonium salts
Original post by I'mComingOxford
thought this would be a easy gcse bio question about protein and i could help for once :cry:


Me too, I'mComingOxford, me too

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