Carbocations in general are stabilized by hyperconjugative interactions where po

Question

Carbocations in general are stabilized by hyperconjugative interactions where possible. The standard picture of this stabilization is illustrated below left (structure 1), with the empty p orbital mixing with an aligned sp3 hybrid C–H bond. The vinyl carbocation 2 presents a variant of this hyperconjugative interaction. Now, an sp2 hybrid is mixing with the empty p orbital. Hyperconjugative interaction 2 differs from the standard model 1 in two important aspects: (1) The hybrid orbital used by the carbon of the C–H bond is different (sp3 in 1 vs. sp2 in 2), and (2) the angle between the C–H bond and the p orbital is different (~ 109º in 1 vs. ~ 120º in 2—Note: the real bond angles are probably a little less in both cases, but we will use the canonical angles for convenience).

Are the changes expressed in 2 more or less stabilizing than the standard model values illustrated with 1?

Select one:

a.

b.

c.

d.

Explanation / Answer

sp2 hybrid carbocation is less stable than sp3 hybrid carbocation.

Therefore, Ans: d

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