When something boils we interrogate the equilibrium........
"Stuff(l) "rightleftharpoons" Stuff(g)"Stuff(l) ⇌ Stuff(g)
In the liquid state, the stuff exerts a "vapour pressure"vapour pressure, which is a function of temperature. When the liquid exerts a vapour pressure that is EQUAL to the ambient pressure, boiling occurs, and bubbles of vapour form directly in the liquid.
The "normal boiling point"normal boiling point is specified when the vapour pressure of the liquid is equal to "ONE ATMOSPHERE"ONE ATMOSPHERE.
To draw your attention to a practical examples, we know that the "normal boiling point"normal boiling point of water is 100100 ""^@C∘C; i.e. at 100100 ""^@C∘C, water has a vapour pressure of 1*atm1⋅atm. At lower temperatures water exerts an equilibrium vapour pressure, which are extensively tabulated, and which often we must take into account when we (say) collect a volume of gas by displacement of water.
In you example, you quote H_3CFH3CF with a boiling point of -78.6−78.6 ""^@C∘C, versus, say, CH_4CH4 with a boiling point of -164.0−164.0 ""^@C∘C, versus, say, CH_2F_2CH2F2 with a boiling point of -52.0−52.0 ""^@C∘C. In this series, dipole-dipole interaction is probably the dominant intermolecular force.
