Plz explain why is the boiling point of dichloroacetic acid is higher compares to monochloroacetic acid. Thkz?

Answer 1

b is partly right:
"Differences in boiling points usually have to do with the forces of attraction between the molecules"

Chlorine is electronegative, meaning it pulls electrons closer to itself. It's effect goes all the way to the O-H of the carboxyl (induction effect) and makes the bond even more polarized (partial negative charge on O and positive on H).

Thus the dichloroacetic acid is more strong as an acid but also the hydrogen bonding between two molecules, through their COOH group, is stronger, since the charges on each end of the O-H dipole become bigger:


R-C=O***H-O-C-R
;;;;;|;;;;;;;;;;;;;;;;;;;||
;;;;O-H********O

I used ; instead of space for drawing and *** for the H-bonds.

So it is a matter of making the interaction stronger, by increasing the energy of the pre-existing H-bonds and not creation of new sites for H-bond formation

Answer 2

Differences in boiling points usually have to do with the forces of attraction between the molecules. Dichloro has a higher boiling point b/c it has 2 chlorine instead of one and chlorine has a high electronegativity (they are very negative). This gives the molecule an extra sites to bond with hydrogen in other molecules (hydrogen bonding)

Answer 3

I would expect the increased polarity due to the additional chlorine atom to be responsible for most of the increase. The additional weight due to the second chlorine atom also plays a (smaller) part.