Question

(a) write the minimal basis set of atomic orbitals for the acetylene molecule.

(b) on the diagram to the right draw in the atomic orbitals that are the main contributors to the molecular orbital on its left. Indicate the phase (positive or negative) of each lobe of each atomic orbital by shading in the negative lobes.

3. Cartoons A-E below show the occupied bonding orbitals of acetylene (ethyne) The lighter shaded lobes are positive, and the darker lobes are negative. Tacetylene (ethyne) Th - CEC - a) Write the minimal basis set of atomic orbitals for the acetylene molecule. (Let the left- hand atoms be HA and CA, and the right-hand atoms be Chand H) b) On the diagram to the right, draw in the atomic orbitals that are the main contributors to the molecular orbital on its left. Indicate the phase (positive or negative) of each lobe of each atomic orbital by shading in the negative lobes. А н с с н н с с н н с с н н с с н с н с с н н с с н D Hc cho нс с н нс с н нс c) List the molecular orbitals A-E in order from lowest energy to highest d) Are any of the orbitals degenerate in energy? If so which ones? e) which orbitals correspond to pi bonds?

Answer 1

a) minimal basis set a atomic orbitals for the acetylene moleculei- The molecule is linear. In the hybrid orbital picture of acetylene, both carbons are sp-hybridized. In an sp-hybridized Carbon, the 2s orbital combines with the 24 orbital to form two sp hybrid arbitals that are oriented at an angle of 180° with respect to each other. The 2py and 2 Pz orbitals remain non hy i non-hybridized and oriented perpendicularly along the y and Z axes, respectively. Carbon: (Tu) [1 69 | -t1111111 25 26 2py 2P2 sp Spy 22 The 'C-('T-bond is formed by the overlap a one 'sp . orbital from each of the carbons, while the two c-H Sigma band are formed by the overlap of the second 'sp. orbital on each carbon with a ls orbital on a hydrogen. Each atoms 2pu, 22 orbitals have half-filled and they form two & Pi (TT) bonds between the carbons, resulting in a triple bend overlap. (one sigma bond to and two pi bonds). H-C=(-H VD OD T-bonding framework t- overlap.

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The molecule is linear. In the hybrid orbital picture of acetylene both carbones are sp-hybridized.