Carbon Compounds
Carbon Compounds tests tetravalency, catenation, saturated and unsaturated compounds, functional groups, IUPAC names, isomers and the chemistry of ethanol and ethanoic acid. Structural formulas matter as much as molecular formulas.
Core rules
- Carbon has four valence electrons and forms four covalent bonds. It can bond with itself, called catenation, forming chains, branches and rings.
- Saturated compounds have only single carbon-carbon bonds; unsaturated compounds have double or triple bonds.
- Functional groups decide chemical properties: -OH alcohol, -COOH carboxylic acid, -CHO aldehyde, -CO- ketone, -Cl haloalkane.
- Isomers have the same molecular formula but different structures. IUPAC naming selects the longest chain and gives the functional group the lowest possible number.
- Ethanol reacts with sodium and burns; ethanoic acid turns blue litmus red and reacts with carbonates to give carbon dioxide. Ethanol and ethanoic acid form an ester with a sweet smell.
Worked example
C2H6O has two isomers. In ethanol, CH3CH2OH, the oxygen is bonded to carbon and hydrogen as an alcohol. In dimethyl ether, CH3OCH3, the oxygen links two carbon atoms as an ether. Both have the same molecular formula, but different structural formulas and different properties. The reasoning is that a molecular formula does not show how atoms are joined.
Traps
Do not treat a molecular formula as a structure. Functional group priority affects naming. Ethanol is an alcohol, not a carboxylic acid. Ethanoic acid is not the same as ethanoic acid's ester. Do not change the carbon skeleton when naming unless the question asks for an isomer.