Question

2. (40 points) The MO diagrams for homon omonuclear diatomic molecules is given below. umolt Anh HOMO Homo a) Bo 8 4 2 No mixing Mixing of, orbitals (a) (b) U2 36 zire .02=642=2e- va) (15 pts) Choose the appropriate diagram for the O molecule and place the right number of electrons. Indicate the frontier orbitals (HOMO and LUMO) and the bond order. b) (20 pts) Sketch a qualitative MO diagram for the heteronuclear diatomic anion CN; place the right number of electrons in the MO's and indicate the HOMO and the LUMO and the bond order. You will need to use the Table of Orbital Potential Energies (attached) to decide how the MO diagram must be modified from the homonuclear to the heteronuclear situation. c) (5 pts) Based on your MO diagram, does CN tend to bind to metals through the carbon atom or the nitrogen atom? Explain why. C CN is a nucleophilic as the negative to the Carbon not on the nitrogon. Hence (N- tend to bind to metals through Carbon abm because it accepts the elections. binds to C beasts SPantcom boguce Homo ersital 225, 22 fete lex Courne har e-deyiz.onc.

Answer 1

opo la mo daglam of Oz -.. 0907 11 i 1411 TEK. TO SPY pre 219 ILL1 - 11 The Tapy,-'' Energy 1 bapa AL as 760 → Since in this Og total e = 8x2 = 16 do 16 electromplaced as ;- 1956 (695* ( 3 )" () Spe) topu) na China

So from this you can calculate bond order of O₂ atom and that would be 1/2( bonding electrons - antibonding electrons )

so it would be 1/2 ( 10 - 6 ) = 2 bond order

* M.O diagram fe a herroatom CNT- Qpz 11 - 1.11 1kp ... у Сару Energy 11- Carbon - Nitragen For CNC, elections = 4+5+1= 10e HOMO = 6gpz Since it is only tighest which is occupied LUMO = Tot Bond order = t[bonding - Arti bonding e] =$(3-2) = 35

The difference in energy levels of Carbon and Nitrogen is due to electronegativity difference between these two .

CN^- is negatively charged and it is the carbon atom on which negative charge occurs and it is only carbon through which it joins to other atom or molecules .

If we look at MO of this molecule we find that sigma 2pz is HOMO among all these which is higher in energies as compared to pi orbitals , and it is nearer to C atom sp orbital so negative charge occurs on Carbon rather than Nitrogen .

This fact can be confirmed by 2 methods

1st we can go for mathematical calculation and find average of sp of Carbon and Nitrogen and then finally we would find that it is only Carbon which is nearer than Nitrogen

2nd we can confirm by overlapping concept , In case of Carbon and Nitrogen s and p orbital overlaps with each other and forms 2 sp orbitals one on Carbon and other on Nitrogen

During subtraction of s and p orbital if forms 2 sp orbitals but lobes on carbon and nitrogen are away from each other in this case and there is greater contribution of C character rather than Nitrogen contribution .

So it is the Carbon which accomodates negative charge and binds to other metal , molecules through carbon only .