What is attachment in alcohols

Alcohols: the OH bond

The O-H bond is more polar than a C-H bond

On this page we want to find out why the hydroxyl group gives alcohols their special physical properties. Let us consider a table with the electronegativities of the main group elements:

The polarity of a covalent bond depends on how different the electronegativities of the two connected atoms are.

In the case of the carbon-hydrogen bond, the EN difference is only 0.4. That's not very much, so the C-H bond is usually referred to as "non-polar", which is not entirely true. The C atom is slightly negatively charged in the C-H bond, the H atom is slightly positive. However, this slight polarity has almost no effect on the physical properties of a hydrocarbon.

With the oxygen-hydrogen bond, things look different. Here the EN difference is 1.4. That is a very high figure. The O-H bond is therefore quite polar. The O atom carries a strong negative partial charge, the H atom a strong positive partial charge. However, this partial charge should not be confused with a "correct" charge, as occurs, for example, with positively charged protons or negatively charged bromide ions. A "correct" charge is much stronger than the partial charges of the atoms of the hydroxyl group.