The relative rates of hydrogen abstraction by the trichloromethyl radical have been determined for nine m-and p-substituted benzaldehydes by means of competitive reactions using ethylbenzene as referecne standard. A polar effect ϱ= 0· 74) was shown to be correlated by the Hammett equation with the σ constant, and the anomalous behaviour of the p-MeO and p-PhO substituents is discussed. The deuterium isotope effect KH/KD was ...