1-chloro-2-methylpropane, ball and stick molecular model. 1-chloro-2-methylpropane is a colourless liquid, a chlorinated derivative of isobutane. It is an isomer of C4H9Cl with a boiling point of 69 degrees Celsius. The more spherical the molecule the lower the boiling point. Black balls are carbon atoms, white balls are hydrogen atoms and the green ball is a chlorine atom.