Editing Organic chemistry (section)

===Functional groups===
[[Image:Acetic acid atoms.svg|upright|thumb|The family of [[carboxylic acid]]s contains a carboxyl (-COOH) [[functional group]]. [[Acetic acid]], shown here, is an example.]]
{{Main|Functional group}}

The concept of functional groups is central in organic chemistry, both as a means to classify structures and for predicting properties.  A functional group is a molecular module, and the reactivity of that functional group is assumed, within limits, to be the same in a variety of molecules. Functional groups can have a decisive influence on the chemical and physical properties of organic compounds. Molecules are classified based on their functional groups. Alcohols, for example, all have the subunit C-O-H. All alcohols tend to be somewhat [[hydrophile|hydrophilic]], usually form [[ester]]s, and usually can be converted to the corresponding [[halide]]s.  Most functional groups feature heteroatoms (atoms other than C and H). Organic compounds are classified according to functional groups, alcohols, carboxylic acids, amines, etc.<ref name=March>{{March6th}}</ref> Functional groups make the molecule more acidic or basic due to their electronic influence on surrounding parts of the molecule.

As the [[Acid dissociation constant|p''K<sub>a</sub>'']] (aka [[Base (chemistry)|basicity]]) of the molecular addition/functional group increases, there is a corresponding [[dipole]], when measured, increases in strength. A dipole directed towards the functional group (higher p''K<sub>a</sub>'' therefore basic nature of group) points towards it and decreases in strength with increasing distance. Dipole distance (measured in [[Angstrom]]s) and [[Steric effects|steric hindrance]] towards the functional group have an intermolecular and intramolecular effect on the surrounding environment and [[pH]] level.

Different functional groups have different p''K<sub>a</sub>'' values and bond strengths (single, double, triple) leading to increased electrophilicity with lower p''K<sub>a</sub>'' and increased nucleophile strength with higher p''K<sub>a</sub>''. More basic/nucleophilic functional groups desire to attack an electrophilic functional group with a lower p''K<sub>a</sub>'' on another molecule (intermolecular) or within the same molecule (intramolecular). Any group with a net acidic p''K<sub>a</sub>'' that gets within range, such as an acyl or carbonyl group is fair game. Since the likelihood of being attacked decreases with an increase in p''K<sub>a</sub>'', [[acyl chloride]] components with the lowest measured [[PKa|p''K<sub>a</sub>'']] values are most likely to be attacked, followed by carboxylic acids (p''K<sub>a</sub>'' = 4), thiols (13), malonates (13), alcohols (17), aldehydes (20), nitriles (25), esters (25), then amines (35).<ref>{{Cite web|date=2010-06-18|title=The pKa Table Is Your Friend|url=https://www.masterorganicchemistry.com/2010/06/18/know-your-pkas/|access-date=2021-03-16|website=Master Organic Chemistry|language=en-US}}</ref> Amines are very basic, and are great nucleophiles/attackers.