Review of functional groups and the main families of reactions
Review: functional groups
Review: functional groups
A functional group gives an organic molecule specific chemical properties, regardless of the length of its carbon chain.
| Group | Formula | Example |
|---|---|---|
| Alcohol | -OH | CH3-CH2-OH (ethanol) |
| Aldehyde | -CHO | CH3-CHO (ethanal) |
| Ketone | -CO- | CH3-CO-CH3 (propanone) |
| Carboxylic acid | -COOH | CH3-COOH (ethanoic acid) |
| Haloalkane | -X (Cl, Br...) | CH3-CH2-Br (bromoethane) |
In addition, there is the carbon-carbon double bond C=C, which characterizes alkenes (for example ethene CH2=CH2), and which is also a preferred reactive site.
Why this review is essential
In advanced organic chemistry, it is not the groups themselves that need to be memorized, but their reactivity: what transformations can each group undergo? This is the subject of this course: understanding the main families of reactions that connect organic molecules to one another.
An example linking several groups
An alcohol such as ethanol can, depending on the conditions, lose its -OH group to form a double bond (giving an alkene), or conversely be oxidized to form an aldehyde and then a carboxylic acid. A single molecule is therefore the starting point for several possible families of reactions.
Common mistake
Do not reduce a functional group to its formula alone: what matters in practice is its position on the chain (end of chain or middle) and its environment, which determine which reactions are actually possible.