The haemoglobin derivative that is formed due to reaction of CO2 with blood is

Reduced hemoglobin: It results from release of O2 from oxyHb. Carbaminohemoglobin:In this, CO2 is attached to the globin pa of Hb. The affinity of Hb for CO2 is about 20 times that for oxygen. Carboxyhemoglobin: Carbon monoxide is attached to Hb where O2 is normally attached. The affinity of Hb for CO is 200-300 times that for O2. It is normally present in small amounts, but in large amount in smokers in whom it impairs O2 transpo. Methemoglobin: When blood is exposed to some drugs, or oxidising agents in vitro or in vivo, the ferrous iron of Hb is conveed into ferric iron, forming metHb, which is dark in color. When present in large amounts, it gives a dusky appearance to the skin. Small amounts of metHb are formed normally but an enzyme system conves it back to Hb.