Distance between atoms in a bond

[zachem62]

Here's the question:

The structure of 1,3-butadiene is usually written as H2C=CH–CH=CH2. The average bond lengths given in Table 9.2 in my textbook are: C–C of 154 pm and C=C of 133 pm. Explain the fact that the observed value of the distance between the two central carbon atoms in 1,3-butadiene is 146 pm.

Are the 2 central carbon atoms the 2 carbons that have a double bond between each other? If so, the distance of C=C is equal to 133pm so why would the distance between the 2 central carbon atoms that are double bonded be different? How else would I answer this question? THanks.

 

[Bystander]

Number the carbon atoms from 1-4, beginning to end of chain; "central" means "middle" of chain.

 

[zachem62]

Number the carbon atoms from 1-4, beginning to end of chain; "central" means "middle" of chain.

so the central carbon atoms would be the ones in CH-CH. But I'm still not getting why the distance between these would be different than the given C-C distance.

 

[Bystander]

You've seen/read a discussion of sp², and/or sp³ hybrid orbitals?

 

[zachem62]

You've seen/read a discussion of sp², and/or sp³ hybrid orbitals?

yeah i have, maybe its super obvious and I'm not seeing the connection?

 

[Bystander]

What are the hybrids for 1, 2, 3, and 4?

 

[Borek]

Google conjugation.

 

[zachem62]

What are the hybrids for 1, 2, 3, and 4?

1 would be sp2, assuming it has 2 bonds to H and one double bond to C2
2 would be sp2, assuming it has 1 double bond to C1, 1 bond to H and another bond to C3
3 would be sp2, assuming it has 1 bond to C2, 1 bond to H and one double bond to C4
4 would be sp2, assuming it has one double bond to C3, and 2 bonds to H