C-H bond

no, martin & LOK, i don't think there's any partial double bond.
the sole reason is as Chow suggest, it's due to energy level of the hybridized orbitals.

in benzene ring, carbon undergoes sp2 hybridization. the unhybridized p-orbital sideway-overlaps with others nearby, giving partial double bond character to the C-C bond. the (conjugated) C-C bond in benzene is stronger than C-C in unconjugated alkanes.

however, please see orbitals in hydrogen. the 1s is involved in bonding (with the sp2 from carbon).
if there's overlapping with p-orbital from carbon, which orbital should hydrogen use?

2s-orbital? note that 2s is spherical while 2p from carbon is dumb-bell shaped. "overlapping" will ultimately lead to zero overlapping (notice the sign on p-orbital). thus 2s-2p overlapping is not possible.
2p-orbital? possible, but energy difference would be to large -- 2p from hydrogen? kidding?


there's partial double bond character in C-C in benzene, but NOT in C-H.

the actual reason behind the difference in C-H bond strength is as Chow suggested, energy level of sp2-hybridized orbitals.
s is lower in energy, while p is higher-energy. mixing (hybridizing) leads to averaging in energy -- this lowers the energy level in sp2 used in bond-formation. more stable in energy level --> less likely to be broken.

C-H bond in the benzene ring is stronger due to partial double bond character.
Delocalization of the electrons in the benzene ring contribute partial double bond in the C-H bond in the benzene ring, so the bong strength is greater than single bond C-H bond in methyl group.

因為係sp2 hybridisation,
有個unhybridised p orbital可以做pi-bond,
因此有重鍵特性i.e.有resonance

你做過AL chem pastpaper?
有一年(2007 or 08)有問呢條
佢個答案係指出 hybridization
所以影響到個bond strength
其實背後既核心係s-character作怪
大學野,但係照考,吹漲