Question

which reaction requires more energy (a) or (b)? Briefly explain this result using resonance structures.

from the calculations, it seems that reaction (a) requires more energy but i'm unsure as to how to use resonance to explain this, thanks!

Part A: Enols and Enolates 1. Build acetone (1) and its corresponding enolate (2) show below in reaction (a). H₃ C CH3 HAC CH, You will need to delete a hydrogen atom in structure 2 by using the red star key. Minimize the structure as you have done before. Setup the calculations and change from a Hartree-Fock calculation to a Sempirical one. For the enolate, you will also need to change the total charge to Anion. Once the calculation is finished, select Display-Properties and record the energy. Note that atoms of the enolate must be planar. This includes both atoms of C-o, the alpha carbon, and atoms attached to these atoms. If it is not planar, set the dihedral angle of 4 consecutive atoms of the enolate to 0 using Geometry:Measure-Dihedral and resubmit. Inot planar planar Energy of (1) -223.98 kJ/mol - 203.51 kJ/mol Energy of (2)

Answer 1

From the resonating structure of enolates as i have shown in the attached sheet (please find it) , it is quite clear that reaction a has one resonating structure to its enolate while in reaction b the enolate has its two resonating structure. More the resonating structure more the stability of compound, Hence the enolate in reaction B will be more stable.

Due to the fact of more stable enolate it formed very easily and got stability. Hence it requires less energy compare to reaction A to form the enolates.

In other way, we can say that the negative charge is delocalised on both two Oxygen atom compared to One oxygen atom in reaction a.

So, It clear that Reaction A requires more energy to form the enolates.

Reaction a- СИ си, И CH, Reaction-b- с (а) не Н® о се