# Hyperconjugation in bridged carbon systems

While studying about hyperconjugation, I came across the following compound which posseses one α-hydrogen (with respect to the $$\mathrm{sp^2}$$ hybridised carbon atom with an empty $$\mathrm{p}$$-orbital), however, apparently does not show a hyperconjugation effect.

This led me to draw an ‘assumption’ that an alpha hydrogen on a bridged carbon atom may not get involved in hyperconjugation when placed next to a carbocation, alkene, free radical, or an arene. Is this true? If so, then why?

• Careful with these kind of compounds; they usually tend to form nonclassical cations. Oct 14 '19 at 23:43
• @Martin-マーチン What do you mean by “non-classical”? Oct 15 '19 at 10:24
• Oct 15 '19 at 13:13

If you look at figure 1 closely, you can see that the empty p orbital and the bridgehead hydrogen σ-bond are almost at a $$90^\circ$$ angle towards each other. For hyperconjugation, you want approximately parallel arrangements, so this obviously fails.
However, you should always be aware that this type of compounds, essentially a norbonyl cation, is essentially the example species for non-classical cations. In this case, instead of a hyperconjugation involving the $$\ce{C-H}$$ bond one essentially expects the $$\ce{C-C}$$ bond of the ‘back half’ of the six-membered ring to provide that hyperconjugation. For a more accurate and detailed explanation, please consult the Wikipedia page or the textbook of your choice.