Question

which among the given acids as lowest pka value:
a) Cl-CH2-COOH
b) Br-CH2COOH
c) O2N-CH2COOH
d) NC-CH2COOH

Answer 1

this is electron reducing effect. the one group with the highest E-WG will be the strongest acid hence lowest pka.

to me cl<br
and no2>nc

an educated guess would say C because NO2 is a knows electron withdrawing group

Answer 2

Acidity increases from left to right and from top to bottom on the periodic table.
Thus, in order of increasing acidity and decreasing pKa values:
NC-CO2COOH<O2N-CH2COOH<Cl-CH2-COOH<Br-CH2COOH.
Br-CH2COOH has the lowest pKa value and is the strongest acid.

Answer 3

the guy above me is incorrect, he is only thinking single atom attached to a proton(H atom)

NO2>CN>br>cl

its due to I- electron withdrawing effect, because of resonance and N has 2 oxygens pulling a dipole or feild shift towrds it with has less electron density around the O-H THATs why and that why for all of these