alcohols and phenols

An industrial process for production of aldehydes from alkenes by addition of a formyl group (CHO) group and a hydrogen atom to a carbon-carbon double bond.
It is done by addition of alkene with high pressures (between 10 to 100 atmospheres) of carbon monoxide and hydrogen at temperatures between 40 and 200 °C. Transition metal catalysts are required.
HCo(CO)3 and HRh(CO)(PPh3)2.
If you want more details, you could refer a standard text book on organic chemistry.

The Importance of this reaction is that aldehydes are sometimes very important for further synthesis of more complex compounds.