Question

5. Molecular orbitals are formed by the overlap of atomic orbitals. Thus, n atomic orbitals can combine (overlap) to form n molecular orbitals. In 1,3-butadiene there are four atomic p orbitals which can combine to form four 7 molecular orbitals. In ethene there are two atomic p orbitals which can combine to form two y molecular orbitals. The drawings below show the different ways in which the p orbitals of ethene and 1,3- butadiene can be combined to form the various molecular orbitals. Draw arrows for the electrons contained in each molecular orbital. Label the combination of p orbitals that gives rise to: a) the LUMO of 1,3-butadiene, b) the HOMO of 1,3-butadiene, c) the LUMO of ethene, and d) the HOMO of ethene. To represent the suprafacial cycloaddition reaction between 1,3-butadiene and ethylene, draw a solid line from the LUMO of 1,3-butadiene to the HOMO of ethene as well as a dashed line from the HOMO of 1.3-butadiene to the LUMO of ethene. 1,3-butadiene ethylene 88804 8888 8888 - nt electrons M.O. Labels electrons M.O. Labels

Answer 1

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1,3-butadiene (0) ethylene for ethene) (=) do so do of o do ob ut LUMO 42 It HOMO HOMO do dodo do 88. 4 — LUMO o OY, Ik 88 It HOMO HOMO @ LUMO of 1,3- butadiene : Yes 8888 In please combination of two Lumos of ethene) { 8 8+88 6 HOMO of 13- butadiene; 4, © Lumo of ethylene Cout of phase combination of two HOMOs of ethene 4₂ = 8 8 out of phase combinations of two parallel .p-orbitals @ HOMO of ethylene : ( In phase combination of Oto Y7two parallel p-orbitals Suprafacial cycloaddition between 1,3-butadiene and ethylene: 43(LUMO) 42 (HOMO) + → = > 884, (HOMO) 8 8 47 (LUMO) N