Why does o-xylene command a higher boiling point than its C8 aromatic isomers?

Why does o-xylene command a higher boiling point than its C8 aromatic isomers?
Among the four C8 aromatics, boiling points sit within a narrow band: para-xylene 138.4 C, meta-xylene 139.1 C, ethylbenzene 136.2 C, and ortho-xylene 144.4 C. The gap looks small but it is decisive for separation economics. Para-xylene is non-polar and packs tightly in the crystal lattice, giving it the highest melting point, which is why industrial separation relies on freeze crystallization rather than distillation. Ortho-xylene carries a modest polarity from its two adjacent methyl groups, lifting its boiling point above the others. That polarity difference is weak, so the boiling spread stays tight and conventional distillation remains impractical for bulk isomer splitting.