Question

I added 2 equiv of p-tolualdehyde to 1 equiv of acetone to make (1E,4E)-1,5-di-p-tolylpenta-1,4-dien-3-one (NMR backed it up). Why is this the only isomer formed? Just sterics or something more?

Answer 1

The formation of the (1E,4E)-1,5-di-p-tolylpenta-1,4-dien-3-one isomer is driven by steric hindrance, electronic effects, and reaction conditions that together favor the stability of the E-E isomer, as confirmed by NMR spectroscopy.

Step-by-step explanation:

The exclusive formation of the (1E,4E)-1,5-di-p-tolylpenta-1,4-dien-3-one isomer can be influenced by several factors including steric hindrance, electronic effects, and the inherent stabilizing interactions that govern such condensation reactions. In this aldol condensation reaction, sterics can significantly guide the formation of the more stable E-E isomer over other potential isomers.

The bulkiness of the p-tolualdehyde groups can impact the dienone's conformation, favoring one that minimizes steric strain. Electronic effects such as the preference for formation of more thermodynamically stable double bonds might also play a key role in determining the regioselectivity and stereoselectivity of the reaction.