alcohol oxidation
Oxidation is how chemists climb the ladder from alcohols up to carbonyl compounds — aldehydes, ketones, and carboxylic acids. In plain terms, oxidation here means removing the hydrogen from the carbon-oxygen (the -OH and the C-H on the same carbon) so that a new pi bond, C=O, can form in its place. The outcome depends entirely on what kind of alcohol you start with.
Whether oxidation can happen, and how far it goes, follows the alcohol's classification. A primary alcohol (R-CH2-OH) has two hydrogens to lose on the carbinol carbon, so it can be oxidised once to an aldehyde (R-CHO) and then, if conditions allow, further to a carboxylic acid (R-COOH). A secondary alcohol (R2CH-OH) has only one such hydrogen, so it stops cleanly at a ketone (R2C=O). A tertiary alcohol (R3C-OH) has no hydrogen on the carbinol carbon at all, so it simply cannot be oxidised this way — there is nothing to remove without breaking a carbon-carbon bond.
The art is in stopping where you want. Strong, classic oxidants like chromium reagents will carry a primary alcohol all the way to the carboxylic acid in water; to halt at the aldehyde you need either a milder, anhydrous chromium reagent (PCC) or a modern selective method (Swern oxidation, Dess-Martin periodinane). The push toward greener chemistry has also brought catalytic oxidations (for example TEMPO with bleach) that avoid toxic, heavy-metal chromium waste.
1-propanol oxidised by PCC stops at propanal (CH3-CH2-CHO, an aldehyde); the same alcohol with hot chromic acid (H2CrO4) goes all the way to propanoic acid (CH3-CH2-COOH). 2-propanol gives acetone (a ketone) either way; tert-butanol gives nothing.
Primary to aldehyde or acid, secondary to ketone, tertiary not at all.
Tertiary alcohols are not oxidised here because there is no C-H on the carbinol carbon to remove; do not confuse this with combustion, where any organic molecule, alcohol or not, burns to CO2 and water.