Editing Halogen (section)

=== Drug components ===
In [[drug discovery]], the incorporation of halogen atoms into a lead drug candidate results in analogues that are usually more [[lipophilic]] and less water-soluble.<ref>{{cite book| first = G. | last= Thomas | title =Medicinal Chemistry an Introduction | publisher = John Wiley & Sons, West Sussex, UK| year=  2000 | isbn= 978-0-470-02597-0}}</ref> As a consequence, halogen atoms are used to improve penetration through [[lipid membrane]]s and tissues. It follows that there is a tendency for some halogenated drugs to accumulate in [[adipose tissue]].

The chemical reactivity of halogen atoms depends on both their point of attachment to the lead and the nature of the halogen. [[Aromatic]] halogen groups are far less reactive than [[aliphatic]] halogen groups, which can exhibit considerable chemical reactivity. For aliphatic carbon-halogen bonds, the C-F bond is the strongest and usually less chemically reactive than aliphatic C-H bonds. The other aliphatic-halogen bonds are weaker, their reactivity increasing down the periodic table. They are usually more chemically reactive than aliphatic C-H bonds. As a consequence, the most common halogen substitutions are the less reactive aromatic fluorine and chlorine groups.