Advices For Studying Organic Chemistry

1) The s-trans conformation of 1,3-butadiene is the predominant one at room

temperature.

13.7C MOLECULAR ORBITALS OF 1,3-BUTADIENE

1. The central carbon atoms of 1,3-butadiene are close enough for overlap to occur
   between the p orbitals of C2 and C3.

Figure 13.4 The p orbitals of 1,3-butadiene, stylized as spheres. (See Figure 13.5 for
the shapes of calculated molecular orbitals for 1,3-butadiene.)

1. This overlap is not as great as that between the orbitals of C1 and C2.


2. The C2–C3 overlap gives the central bond partial double bond character and
   allows the four π electrons of 1,3-butadiene to be delocalized over all four
   atoms.

2. The π molecular orbitals of 1,3-butadiene:
   
   
   1. Two of the π molecular orbitals of 1,3-butadiene are bonding molecular orbitals.
      i) In the ground state these orbitals hold the four π electrons with two spin-paired
      electrons in each.
   
   
   2. The other two π molecular orbitals are antibonding molecular orbitals.
      i) In the ground state these orbitals are unoccupied.
   
   
   3. An electron can be excited from the highest occupied molecular orbital (HOMO)
      to the lowest unoccupied molecular orbital (LUMO) when 1,3-butadiene absorbs
      light with wavelength of 217 nm.