Acidic C-H protons:

Most acidic protons are attached to heteroatoms like halogen, oxygen, and nitrogen. Protons attached to carbon are not generally acidic but there are exceptions. One such type of exception takes place with aldehydes or ketones while there is a CHR₂, CH₂R or CH₃ group next to the carbonyl group. The protons pointed out are acidic and are attached to what is termed as α (alpha) carbon. They are there- fore known as α protons.

Figure:  Acidic α protons.