Question

To compare the acidity of two organic acid, we must the y of their conte bases. The more stable the conjugate base, the stronger the acid. To determine if the conte base is stable, we must follow the below less Negative charges are more stable on trov o LF, Br Larger atoms with negative charge more stable Negative changes preferoide one s than on more electronegative Negative changes to be placed intoms with the more character so they prefers over overset Neighboring ctronegative atoms delocal anegative change thus making the molecule much more stable Addition , the presence of resonance in C h ase increases is stability Circle the stronger acid 1. HFo HCI 2. HS of H, 3. CH CH CH.CH hone

Answer 1

The points to keep in mind while checking the stability of conjugate bases are:

1,4,5,6

a) negative charges should be on more electronegative atoms like Cl, F, Br

Because negative charges on less electronegative atoms or electropositive atoms will destabilize the structure.

b) negative charges prefer the orbital s over sp then sp2 and then sp3.

Because of electronegativity order of orbitals which is as:

s > sp > sp2 > sp3

c) neighbouring electronegative atoms disperses the negative charge to stable the structure by its electron withdrawing effect

d) resonance always increase the stability of structure

Stronger acids are:

1) HCl than HF

because F is more electronegative than Cl so H-Cl bond is less stronger than H-F , so can be break easily and donate proton easily. Thus HCl is more acidic.

2)H2S is stronger acid than H2O.

Because S is of much larger size than O, so H-S bond is longer and weaker than H-O, so easy to break. Thus H2S give proton more easily.

3) CH2=CH2 more acidic thand CH3CH3

Because in ethene c is sp2 hybridized, but in ethane c is sp3 hybridized, thus ethene carbon is more electronegative than ethane, and so more acidic.

4) 2-chloropropanoic acid (a) is more stronger than 3-chloropropanoic acid (b)

Because Chlorine due to its electron withdrawing nature (-I effect) increase the stability of conjugate base of acid by dispersing negative charge of coo- and as distance of chlorine from coo- ion increases, its effect decreases because inductive effect is distance dependent. So (a) is stronger acid because here cl is at 2-position but in (b) Cl is at 3-position.

5) (a) is more acidic than (b)

6) phenol (b) is more acidic than allyl alcohol (b)

Because phenoxide ion ( conjugate base of phenol) is more stabilised by resonance .