Compression required to "diesel" petrol (gasoline) is lower, which is why some autos have the problem of continuing to run ("diesel") after the ignition (and spark) are shut off. Most now incorporate other controls and limiters, such as controlled fuel injection, to eliminate this.

Gasoline is comprised of a shorter set of hydrocarbons (mostly 6, 8, and 10 chain) than diesel (about 12-16 chain length, though 8-21 carbon are listed at Wikipedia). Volatility (and ignitability) increase with shorter chains -- methane (C2H6) and butane (C4H10) -- that is, two and four chain hydrocarbons -- are both gaseous at or near room temperature.

Longer chains still get you heavy fuel oils, tars, etc.

actually it's the opposite, you could run a diesel car on gasoline if you wanted (not wise as diesel fuel is actually used as a lubricant in high pressure fuel pumps)