Question

Carbon monoxide (CO) forms bonds to a variety of metals and metal ions. Its ability to bond to iron in hemoglobin is the reason that CO is so toxic. The bond carbon monoxide forms to metals is through the carbon atom: M -C= 0 a. On the basis of electronegativities, would you expect the carbon atom or the oxygen atom to form bonds to metals? b. Assign formal charges to the atoms in CO. Which atom would you expect to bond to a metal on this basis? c. In the MO model, bonding MOs place more electron density near the more electronegative atom. (See the HF molecule in Figs. 9.42 and 9.43.) Antibonding MOs place more electron density near the less electronegative atom in the diatomic molecule. Use the MO model to predict which atom of carbon monoxide should form bonds to metals.

Answer 1

Ans: · Thebond Caerobon monoxide frooms to metale is thorough the Carbon atom: M-C=0 ( ) In Carbonmonoxide moleccele Oxygen atom is more electronegative than the Caribon atom .... Set 20 (on the basis of electronegativity of the atoms) Thus, on the basis of electronegativities, the oxygen atom should have more accumulation of negative charge as it contains more electron densities." So, the oxigen atomes should from bonds to metals. (b) The fermal change on anatom in a molecule (90) anus - [2 x Mop t nomb] nuse numbers of valence C elections nomb a numbers of non bonding electone Mbps number of bonding electrone

C=0 & Inco, The formal charge on carbonce)s.. 2p(- 4-[£x6+2] 24 - [3 +2] » -1 The formal change on oxygen atom (0) 90(0)'> 6-[£x6 +2] 56-[3+2] » +1 Thus, C= ŏ , On the basis of formal change calculation, the carbon atom should from bonds to a metal. Because here inco, the Carbon atom contains one unit of negative change (-1) than the Corresponding morre electronegative oxygenatom chich contains' a single cinit of positive chavege(tl), Due to the presence of pasitive charge on oxygenatom band foromatinu via , Oxygen atom is not fenoetable. Thus. @ #

(C). Mokularo orobital diagnomme of co! Electronic Configeveation of carbon » Is s'apt cond the electronic Configeocation of oxygend a 1s'es'2px Now, onlap considersing the valance osobitele (25, 2p) of Carbon at and oxygen We construct a Modiagram of co molecule. to Shoot 2py? espade MOMO 28 * 4180) pure Hybrid Sitemic (s-pmixing) 20 coobital of Coeben th ... 1016 YlSplit h28 Mor ofco Hybrid . (s-pmixing pane atomic "As oxygen is more electronegative So ito." ombitel of atomic energy levels aree energitically some oxygen Towero than the Carbon atom!

- From the MO diagramme of co, it is clear that the highest occupied molecular orbital (HOMO) is the 35hb orbital which is non-bonding in natures but energitically more close to the Carbon atomic Coobitels. So, on the basis of MO modeli in co; the Carobon (e) atom should from bonds to metals. Also, as the x* antibonding orbitals are more close to Cambon so, it can accept electrons in the *orbital from the metall during t-back donation. Hence the metal co bond strength will enhance.