Carbon dioxide and carbon monoxide...

[Royston]

I've just been studying converting carbon dioxide to carbon monoxide, by heating carbon through a current of CO2. What I can't understand is how reducing the ratio of oxygen to carbon, somehow makes a deadly gas.

 

Sorry is this is a stupid question. I can't remember hardly any chemistry I learnt at school, and I've only just started studying the subject again over the last couple of days.

[insane_alien]

Carbon monoxide can bind very strongly to the the iron centre in haemoglobin. more strongly than oxygen. basically it stops your blood carrying oxygen. in the short term, this is an accumulative effect. but the "bad blood" would work its way out of your system. assuming you were still alive and didn't breathe any more CO.

[Royston]

Thanks insane_alien, that's helped alot.

[Tartaglia]

In CO2 all the valence electrons for carbon are used for bonding. In CO there is a triple bond due to a dative pi interaction of the oxygen and carbon orbitals. This leaves a lone pair on the carbon. Normally lone pairs on elements which are not especially electronegative like carbon are not good ligands due to the poor sigma donating ability. However the multiple bond of the CO has appropriate pi* antibonding orbitals of the same symmetry as the d orbitals as the metal, this allows pi back donation into the CO pi* orbitals, similtaneously weakening the CO bond and strengthening the Metal -C dative bond. This is what makes it such an effective haemoglobin blocker