Organic
Functional Groups:
Aldehydes, ketones, 1° alcohols, etc.
Organic chemistry is dominated by the "functional group approach", where organic molecules are deemed to be constructed from: An inert hydrocarbon skeleton onto which functional groups (FGs) are attached or superimposed.
The functional group approach "works" because the properties and reaction chemistry of a particular functional group (FG) can be remarkably independent of environment.
Therefore, it is only necessary to know about the chemistry of a few generic functions in order to predict the chemical behaviour of thousands of real organic chemicals.
Organic molecules are also named using the functional group approach:
2-hexanone
2-hexanol
2-chlorohexane
The rule is that functions assume their distinct identity when separated by –CH2– groups. Thus, the carbonyl, C=O, and hydroxy, OH, of a carboxylic acid, RCOOH, are part of a single function and are NOT "alcohol-plus-ketone":
A Couple of Words About The Functional Group Approach
The functional group approach is 100% empirical in that it is determined by experiment and experience, and not by theory (unlike VSEPR, for example.)
A multifunctional entity like the drug molecule morphine has several functional groups and chiral centres:
Professional chemists consider large multifunctional organic molecules in terms of 'substructures' rather than functional groups. Ring systems, for example, are better considered as substructures, although the dividing line can be fuzzy...
What You Need To Know
To be proficient in organic chemistry at university entrance level [ie, American AP, British A-Level or French Baccalaureate] exam systems,
in other words be able to:
name organic molecules
predict solubility in different types of solvent
predict chemical reactivity
predict spectra
it is absolutely essential to be able to recognise the 30 or so functions listed below. For a more comprehensive list of organic FGs, try the Chemogenesis Web Book FG Database: