AbstractThe prototropic rearrangement of 3‐phenyl‐1‐propenes to the corresponding 1‐phenyl‐1‐propenes was investigated in basic media utilizing 0.1M sodium ethoxide in absolute ethanol at 81°C. It was found that the effect of substituents on the rate of such isomerizations follows the order: p‐NO2 > o‐Cl > m‐Cl ≥ m‐F > p‐Br > o‐CH3 > m‐CH3 > m‐CH(CH3)2 > p‐CH(CH3)2 ≥ p‐C(CH3)3 > o‐OCH3. This is consistent with first‐order kinetics and “BS” mechanism. Quantitative treatment in terms of Hammett's equation showed a straight line, with a slope (p value) of +2.25. An increase in the strength of the base was also found to cause an increase in the rate of isomerization.