IIT JEE , AIEEE Forum - Chemistry , Organic Chemistry

iitjee08aspirant

in amino acids chap general que is that they will give pka of carboxylic grp and amino grp and give the pH of the system ......then they ask to find whether amino grp will exist in protonated form or carboxylic acid will exist in anion form etc.....
im not able to solve them....
cud anyone plzz explain how to solve them????

varshavallig

just remember this,
if pH<7=======>ion moves towards cathode=====>in carboxylic acid form as thee will be more H+in acidic condition.
if pH>7=======>ion moves towards anode====>in amine form as there will be OH- in basic condition.
hope this helps
!!!!!!!!!!!!!!!

varshavallig

at isoelectronic point it neither moves towards cathode nor towards anode.it exists as zwitter ion.===>

(+)NH3-CH(R)-COO(-) R is alkyl group
!!!!!!!!!!!!!

iitjee08aspirant

cud u make it more clear ... i mean if pH>7 then wat will exist in wat form....like will amino grp be protonated????
wat abt comps having two amino grps and one cARboxyloic...etc

varshavallig

normally it exists as zwitter ion.(as shown previously)
in pH<7,protonation will take place,so carboxylic acid ion will get H+ and it exists as acid,it will have NH3+ ion.
if pH>7,deprotonation will take place from NH3+ group,so it exists as amine,it will have COO- ion.
hope its clear
if not feel free to ask
!!!!!!!!!!!!!!!

eistien

i a normal medium ie pH =7 an amino acid will exist as a zwitter ion when pH<7 then basically the solvent is more acidic and the amino acid behaves more of a base and NH3+ exists where as when pH>7 the solvent is basic and thus the amino acid behaves a s an acid and COO- exists!!!now understood!!!!

layman

To all of you it need not exist as a zwitterion at pH=7. Only at isoelectric pH it exists as a zwitterion.

layman

It depends upon the type of amino acid:basic or acidic or neutral.

iitjee08aspirant

thanks to all of u....

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