Which species is more stable?

Name: Problem 7, Chapter 7: Organic Chemistry
Uploaded: 2021-07-27T18:08:33-08:00
Duration: 6 min 52 s
Channel: Caleb Prus
Description: Which species is more stable?

Key Concepts

Thermodynamic Stability

This concept refers to the overall energy level of a species. A more thermodynamically stable species resides at a lower energy state compared to less stable species. Stability is judged based on the relative free energies and how well the structure minimizes internal strain and repulsive interactions.

Resonance Stabilization

Resonance stabilization occurs when a molecule can delocalize electrons across different atoms through overlapping p-orbitals. This electron delocalization distributes charge over a larger framework, lowering the overall energy and increasing the stability of the species.

Hyperconjugation

Hyperconjugation is the stabilizing interaction that results from the overlap of sigma bonds (typically C–H or C–C) with an adjacent empty or partially filled p-orbital or a ?-system. This effect disperses charge and contributes to the stability of reactive intermediates or charged species.

Inductive Effects

Inductive effects arise from the electronegativity differences between atoms in a molecule, which cause electron density to shift through sigma bonds. Electron donating or withdrawing groups exert these effects, thereby stabilizing or destabilizing the species depending on the nature and position of the substituents.

Steric Effects

Steric effects relate to the spatial arrangement of atoms within a molecule. Excessive crowding or unfavorable spatial interactions can increase the energy of a species, reducing stability. Conversely, a well-organized structure with minimal steric hindrance is typically more stable.

Transcript

00:01 We're asked to find which of these species is more stable.

00:03 And when considering stability, we need to think about the possible resident structures that each of these species can have, which can lend to electron delocalization, therefore lower energy.

00:15 So we're going to start by doing some arrow pushing to figure out which can have residence species and which resident species are more stable and greater contributors.

00:25 So with this one, we can do some arrow pushing here.

00:31 We've got a single arrow.

00:33 So we can move the double bond and the radical.

00:37 And we can form this resonance structure here, where we now have the radical on the secondary carbon, and we've moved the double bond.

00:54 And we can do the same thing with this, where we have single arrows, here but in this case we form a molecule with a primary radical instead of a secondary radical and remember that secondary carbons are more stable because of the hyper conjugation of the surrounding carbon hydrogen sigma bonds so actually this species here is more state this is a more resonant structure.

01:34 I'll just kind of indicate that these are resonant structures.

01:37 This is a more stable resonance structure here because we have the radical on the second carbon instead of the primary carbon here.

01:45 We can see that there's two carbons attached to it, whereas here we only have one carbon attached to that.

01:53 So that's a primary carbon.

01:55 Okay.

01:56 So moving on, what about b? so b, we can form actually a we can form an enolate, excuse me.

02:09 In both of these we can actually form the enolate.

02:12 And that, oops, oops, it's a little laggy here, sorry about that.

02:22 In this case, we have the negative charge on the oxygen, and we form a carbocan.

02:42 Whoops, so now.

02:45 So now, now, now we have the negative charge on, i forgot to draw that arrow there.

02:52 Okay, i think we're good.

02:53 I think this is the enolates.

02:56 And we have a positive charge on this position here...

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