Predicting Stability of E/Z Isomers?

📌 CONCEPT: The stability of E/Z isomers in a compound can be predicted by considering the steric hindrance and the degree of bond conjugation of the molecule. In general, the isomer with the more stable conformation is the one that has the least steric hindrance and maximum bond conjugation.

📐 RULE / FORMULA: The main principle behind predicting the stability of E/Z isomers is the principle of least steric hindrance. According to this principle, the isomer with the least steric interaction between the substituents attached to the double bond will be more stable.

💡 WORKED EXAMPLE: Consider the given compound (CH3)3CCH=CHCH3, which exists as two isomeric forms. The E-isomer (on the left) has the methyl groups in the more stable equatorial positions, resulting in less steric hindrance. In contrast, the Z-isomer (on the right) has the methyl groups in the less stable axial positions, resulting in more steric hindrance. Therefore, the E-isomer is more stable than the Z-isomer.

⚠️ COMMON MISTAKE: Students often ignore the steric hindrance factor while predicting the stability of E/Z isomers, which can lead to incorrect conclusions.