Functional group

A functional group is an identifiable group of chemical atoms associated with characteristic chemical reactions. In step-growth polymerization, $A$ and $B$ name compatible reactive groups, not necessarily entire monomers or particular chemical elements.

A carbon center bearing one hydrogen and three other single bonds.

A thioether linkage $\mathrm{R}-\mathrm{S}-R\prime$. sulfur lone pair participation can generate cyclic sulfonium intermediates during substitution.

The group $\mathrm{PhC}\equiv \mathrm{C}-$, with the dash indicating attachment. It has no remaining terminal acetylenic hydrogen.

The C–N–N grouping of a diazo compound, with important octet contributors $\mathrm{C}={\mathrm{N}}^{+}={\mathrm{N}}^{-}$ and ${\mathrm{C}}^{-}-{\mathrm{N}}^{+}\equiv \mathrm{N}$. The electronic structure is delocalized over the connected framework.

The group $\mathrm{C}{\mathrm{H}}_2=\mathrm{CHC}{\mathrm{H}}_2-$, attached through the saturated carbon adjacent to the double bond.

The group $\mathrm{C}{\mathrm{H}}_2=\mathrm{CH}-$, attached through an alkene carbon. It differs from an allyl group, whose attachment includes an intervening methylene.

The group PhCH2−, distinct from the two-carbon linker in a phenethyl group.

A divalent CH2 unit within a structure. Its two hydrogens can be equivalent or nonequivalent depending on symmetry, stereochemistry and environment.

The CH3− structural group, with the dash indicating attachment rather than a negative charge when used as a group formula.

The group PhCH2CH2−, distinct from benzyl PhCH2−. Counting the two carbons between a phenyl group and the attachment site prevents a common synthetic-target error.

A sulfonic-acid-derived anion or group, with negative charge delocalized over oxygen atoms. Carbon–oxygen substitution of an alkyl sulfonate differs from attack at sulfur.

The salt ${\mathrm{Na}}^{+}[{\mathrm{O}}_3\mathrm{S}(\mathrm{C}{\mathrm{H}}_2{)}_4\mathrm{OC}{\mathrm{H}}_2\mathrm{C}{\mathrm{H}}_2\mathrm{C}{\mathrm{H}}_3{]}^{-}$, a product of n-propoxide ring opening of a four-carbon sultone. The ether is at the former oxygen-bound terminal ring carbon.

A sulfoxide has two carbon substituents, an oxygen and a stereochemically relevant lone pair at sulfur. Different carbon substituents can make sulfur a configurationally persistent stereogenic centre.

A sulfone contains an $\mathrm{R}-\mathrm{S}(\mathrm{O}{)}_2-R\prime$ group. An aryl sulfone withdraws electron density and commonly directs electrophilic aromatic substitution to meta positions.

$\mathrm{C}{\mathrm{H}}_2=\mathrm{CHS}{\mathrm{O}}_2\mathrm{Ph}$, an activated dienophile whose sulfone group can be removed reductively after cycloaddition.

An ethoxy group is $-\mathrm{OC}{\mathrm{H}}_2\mathrm{C}{\mathrm{H}}_3$. An aryl ethoxy group can donate an oxygen lone pair into an aromatic ring.