Laser flash photolysis studies on alpha-methylbenzylchlorodiazirine, n-propylchlorodiazirine, and isopropylchlorodiazirine have been carried out at low temperatures, ranging from 170 to 230 K. The present results, together with those previously obtained with benzylchlorodiazirine and methylchlorodiazirine, provide a direct measurement of the "by-stander effect" of alkyl substituents on the C atom in the alpha position of the carbene center. Intermolecular reactions of alpha-methylbenzylchlorocarbene and tetramelhylethylene in isooctane and methylcyclohexane have been measured but this reaction is shown to be too slow to measure by LFP in highly viscous decalin solvent.