pKa of acetic acid is 4.75 whereas of glycine is 2.93. So whey is it more acidic? Simarly, why is the amino group "less" basic (9.6 vs 10.6) please provide an easier to understand explanation
Basically, the acidicity of -COOH group depends on how much hydroxyl bond is polarized. The more the common electron pair of OH is withdrawed towards oxygen, the more the acidicity is. Hence, groups with electron withdrawing effect increase the acidicity of caroxylic acid. In acetic acid, -COOH is bound to methyl group which is electron donating group while in glycin, a hydrogen in methyl group was replaced by amino group which is electron withdrawing group. So the aciditicy of -COOH in glycine is larger than in acetic acid
See: http://books.google.com.au/books?id=9Np_Yue4-vgC&pg=PA32&lpg=PA32
Hope that helps
check out chapter four from this book, nice one to understand acidity and basicity of organic molecules.
http://books.google.com.my/books?id=y-O1mo6Lg2wC&printsec=frontcover&source=gbs_ge_summary_r&cad=0#v=onepage&q&f=false
Basically, the acidicity of -COOH group depends on how much hydroxyl bond is polarized. The more the common electron pair of OH is withdrawed towards oxygen, the more the acidicity is. Hence, groups with electron withdrawing effect increase the acidicity of caroxylic acid. In acetic acid, -COOH is bound to methyl group which is electron donating group while in glycin, a hydrogen in methyl group was replaced by amino group which is electron withdrawing group. So the aciditicy of -COOH in glycine is larger than in acetic acid
In glycine there is a negative inductive effect on carboxylic acid due to the amino group and this effect cause to increase the acidity of carboxylic acid There is also a negative inductive effect on amino group due to carboxylic acid and this cause the decrease the basicity of amino group.
In addition to Yalagala notification it's zwitterionic form in AA make this changes in acidity and basicity .
Additional info: The negative inductive effect of substiuent (amino group) leads to stabilization of the carboxylate ion owing to delocalization of electron on the conjugate base, hence the increase in proton concentration - higher ionization constant (increased acidity).
The acidity of organic compounds depends on the nature of electron donating and electron withdrawing groups. The electron withdrawing groups withdraws negative charge from the carboxylate anion and thus increases its acidity. The electron donating groups on the other hand increases charge density of the carboxylate anion and therefore decreases acidy. Since carboxylic acids contain electron donating alkyl groups, therefore they decrease their acidity and thus they have higher pKa values. On the other hand amino acids have electron withdrawing -NH2 groups and they increase the acidity of amino acids. Thus amino acids have lower pKa values.
Olakunle has it right. The way to think about this is in terms of the stability of the conjugate base. look at arginine, the pKa of the side chain is high.~12, Why? because conjugation stabilization of the conjugate ACID. That extra proton is stable in the acidic form of the molecule. Same idea for glycine, once the proton leaves, say at pH 3, the NH3+ somewhat nearby will stabilize the negative charge. Acetic acid has no such feature. Methyl groups do very little in the way of dispersing charge. They in-fact can be thought of a sort of barrier between charges. longer chain = bigger wall.
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