AS Level Chemistry · An introduction to AS Level organic chemistry. A short explanation of the idea, the rules to remember, the mistake to avoid, a worked example and practice questions with answers.
A hydrocarbon contains carbon and hydrogen atoms only. Alkanes are the simplest hydrocarbons and have no functional group. Most other organic compounds contain a functional group, an atom or group of atoms that decides how the compound reacts.
The same molecule can be written in several ways. The molecular formula counts the atoms. The structural formula shows the groups in order, such as CH3CH2OH. The displayed formula shows every bond. The skeletal formula shows only the carbon chain as a zig-zag line, with the functional groups.
A systematic name has a stem for the longest carbon chain, a suffix or prefix for the functional group, and numbers for the positions.
Students often name an ester the wrong way round. The group joined to the single-bonded oxygen is the alkyl part and is written first; the part containing C=O gives the -oate ending.
Answer: 3-methylpentan-2-ol, molecular formula C6H14O.
Try each one, then open the answer.
Answer: A. Count every atom: carbons 2 + 1 + 1 = 4; hydrogens 3 + 2 + 3 = 8; oxygens 2. The molecular formula is C4H8O2.
Answer: C. The –CHO group is an aldehyde, named with the ending -al; four carbons in total gives butanal. Butanone is the ketone CH3COCH2CH3.
Answer: B. Ethanal, C2H4O, and propanone, C3H6O, fit CnH2nO. CnH2n+2O fits alcohols, CnH2nO2 carboxylic acids and esters, and CnH2n alkenes.
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