Functional groups are specific groups of atoms or bonds within molecules that are responsible for the characteristic chemical reactions of those molecules. The same functional group will undergo the same chemical reactions, regardless of the size of the molecule it is a part of. Atoms in functional groups are linked to each other, and the group is linked to the larger molecule, by covalent bonds. Specific members of functional groups can appear as lone molecules or attached to other molecules, which may or may not be or contain other functional groups.
Hydrocarbons are functional groups that contain only carbon and hydrogen, but differ in the number and order of bonds and have different reactivity.
- Alkane: Alkanes consist of either a central carbon or a chain of central carbons and the hydrogen atoms connected to them. Each carbon atom has four single bonds that are either carbon to carbon or carbon to hydrogen.
- Alkene: Alkenes contain at least one carbon to carbon double bond. There may or may not be multiple carbon to carbon double and/or single bonds. The remaining bonds are single bonds to hydrogen atoms, except for where the group attaches to another molecule.
- Alkyne: Alkynes contain at least one carbon to carbon triple bond, though there may or may not be more triple, double, or single bonded carbons involved. The remaining bonds are single bonds to hydrogen atoms unless bonded to another molecule.
- Benzene Derivatives: Benzene is an organic compound with the chemical formula C6H6. The carbons are bonded in a ring form, with the hydrogen atoms bonded to the outside. Benzene derivatives are made by replacing one or more of the hydrogen atoms with another functional group.
Halogen groups, also known as haloalkanes, are functional groups characterized by a carbon to halogen bond. They are very similar to alkanes, but have a halogen bonded to the central carbon. Halogen groups readily undergo nucleophilic substitution and elimination reactions. Depending on which halogen is bonded to carbon, the bond can be anywhere from relatively weak to fairly strong.
- Fluroalkane: The carbon to fluorine bond is one of the strongest covalent bonds found in organic chemistry. Fluorine has the highest electronegativity of all the elements. This causes a high dipole moment in the carbon fluorine bond.
- Chloroalkane: Chloroalkanes are denser than normal alkanes and even water. This is due to chlorine's mass being greater than hydrogen's. Chloroalkanes are not as reactive as some of the other haloalkanes, and make versatile building blocks in organic chemistry.
- Bromoalkane: Most bromoalkanes are relatively nonpolar. Bromine has a higher electronegativity than carbon, so the the carbon in the carbon to bromine bond is electrophilic.
- Iodoalkane: Iodoalkanes are found widely in organic chemistry, but rarely in nature. Almost all iodoalkanes feature a single iodine bonded to a single central carbon. The carbon to iodine bond is the weakest of the carbon – halogen bonds.
Oxygen containing functional groups feature an oxygen bonded to a carbon. The location and hybridization of the carbon to oxygen bond determines the reactivity of the compound.
- Alcohol: An alcohol is any compound in which a hydroxyl group (OH) is bound to a carbon atom through a single covalent bond between the hydroxyl oxygen and the carbon.
- Ketone: Ketones are simple compounds that feature an oxygen double bonded to a carbon, which is then bonded to other compounds. Ketones are considerably more acidic than alkanes and more resistant to oxidation than aldehydes.
- Aldehyde: Much like ketones, aldehydes feature an oxygen double bonded to a carbon that is then bonded to another compound. The difference is that the carbon is also single bonded to a hydrogen atom that is not present in ketones. They are very susceptible to oxidation, and degrade when exposed to air.
- Acyl Halide: Acyl halides also feature an oxygen double bonded to a carbon. The structure is similar to that of an aldehyde, but the hydrogen atom is replaced with a halogen atom.
- Carbonate: Carbonates feature an oxygen double bonded to a carbon. The carbon is then single bonded to two oxygen atoms, which are each then bonded to another atom or molecule. These carbonate esters, as they are also called, either act as links between two other molecules or as links in a chain of carbonates called polycarbonate.
- Carboxylate: Carboxylate is a salt or ester of carboxylic acid. They feature a central carbon single bonded to one oxygen and double bonded to another, then single bonded to another molecule or atom.
- Carboxylic Acid: Carboxylic acid features a central carbon double bonded to an oxygen and single bonded to the oxygen of a hydroxyl group, then single bonded to another molecule or atom.
- Ester: An ester is any compound derived from an acid, usually carboxylic acid, in which at least one hydroxyl group is replaced by an alkyl group, which is an alkane missing one hydrogen.
- Peroxide: Peroxides feature two central oxygen atoms single bonded to each other, then each single bonded to some other functional group or hydrogen. If both are bonded to single hydrogen atoms, it is called hydroperoxide. The bond between the oxygen atoms is very weak, leaving peroxides prone to breaking down into free radicals.
- Ether: Ethers feature a central oxygen single bonded to two alkyl groups (alkanes missing a hydrogen) or aryl group (aromatic ring compound). Symmetrical ethers have either two alkyl groups or two aryl groups. An asymmetrical ether features one alkyl group and one aryl group.
- Hemiacetal: Hemiacetals are compounds derived from aldehydes, and are formed by the addition of an alcohol to the carbonyl (carbon-oxygen) group.
- Hemiketal: Hemiketals are compounds derived from ketones, and are formed by the addition of an alcohol to the carbonyl (carbon-oxygen) group.
- Acetal: Acetals are formed when the alcohol in a hemiacetal group is replaced with an alkoxy group, or an oxygen single bonded to an alkane.
- Ketal: Ketals are formed when the alcohol in a hemiketal group is replaced with an alkoxy group, or an oxygen single bonded to an alkane.
- Orthoester: An orthoester is formed when three alkoxy groups attach to one central carbon atom. Orthoesters are readily hydrolized in mild aqueous acid to form esters.
These groups feature a central nitrogen atom, which can be bonded to hydrogen atoms, carbonyl groups, or other functional groups.
- Amide: There are three forms of amides. The most common, carboxamides, feature a carbon double bonded to an oxygen and single bonded to either a hydrogen or some other organic group. This carbon is also single bonded to the central nitrogen, which is then also single bonded to two other hydrogen atoms or organic groups. Phosphramides have the carbon replaced with a phosphorus. The phosphorus is then double bonded to an oxygen and single bonded to two organic groups or hydrogen atoms. Sulfonamides have the nitrogen single bonded to two organic groups or hydrogen atoms and a single sulfur, which is then double bonded to two oxygen atoms and a single hydrogen or organic group.
- Amine: Amines are ammonia derivatives. Ammonia is a single nitrogen atom single bonded to three hydrogen atoms. Amides occur when one or more hydrogen is replaced with another functional group or atom. Primary amines have one hydrogen replaced, secondary amines have two hydrogen atoms replaced, and tertiary amines have all three hydrogen atoms replaced.
- Imine: Imines feature a carbon double bonded to a nitrogen. The nitrogen is single bonded to either an organic group or a hydrogen atom. The carbon is single bonded to two hydrogen atoms or organic groups.
- Imide: Imides feature a central nitrogen single bonded to two carbons and either a hydrogen atom or another organic group. Each carbon is then double bonded to a single oxygen and either hydrogen or an organic group.
- Azide: The azide functional group take two forms. In the first, one nitrogen single bonded to either a hydrogen atom or organic functional group is single bonded to another nitrogen, which is then triple bonded to a third nitrogen. In the other, the central nitrogen is double bonded to both outer nitrogen atoms. The hydrogen atom or organic group is still single bonded to one of the outer nitrogen atoms.
- Azo Compound: Azo compounds are two nitrogen atoms double bonded to each other. Each nitrogen is also single bonded to either a hydrogen atom or an organic functional group.
- Cyanates: The cyanate ion is a single oxygen single bonded to a carbon that is triple bonded to a nitrogen. As a functional group, the oxygen is double bonded to the carbon, which is then double bonded to the nitrogen. This leaves the potential for one single bond to the nitrogen, which will either be hydrogen or an organic group.
- Nitrates: As functional groups, these are also called nitrate esters. They feature a nitrogen atom single bonded to two oxygen atoms and double bonded to a third. One of the oxygen atoms single bonded to the nitrogen is also single bonded to either a hydrogen atom or an organic group.
- Nitrile: A nitrile is a carbon triple bonded to a nitrogen atom and single bonded to either a hydrogen atom or another organic group.
These are functional groups containing sulfur bonded in a variety of ways to some organic group. The sulfur groups have some unique chemistry thanks to sulfur's ability to form more bonds than oxygen and carbon.
- Thiol: A thiol is an organic functional group in which one sulfur atom is single bonded to both a hydrogen atom and an organic compound.
- Sulfide: Sulfides as organic functional groups are almost identical to ethers, except that instead of an oxygen, a sulfur is present.
- Disulfide: Disulfides are much like sulfides, but with two sulfur atoms. Each sulfur is single bonded to each other and to its own organic group.
- Sulfoxide:Sulfoxides contain a sulfur and oxygen double bonded to each other. The sulfur is then single bonded to either two organic groups or one organic group and a hydrogen atom.
- Sulfone: Here, a central sulfur is double bonded to two oxygen atoms and single bonded to two, usually different, organic groups or one organic group and a hydrogen atom.
- Sulfinic Acid: Sulfinic acid is a sulfoxide with the hydrogen or one of the organic groups replaced with a hydroxyl group.
- Sulfonic Acid: Sulfonic acid is a sulfone with the hydrogen or one of the organic groups replaced by a hydroxyl group.
- Thiocyanate: There are two types of thiocynate functional groups. Thiocynates feature a central sulfur single bonded to an organic group and single bonded to a carbon, which is then triple bonded to a nitrogen. Isothiocynates feature a central nitrogen single bonded to an organic group and double bonded to a carbon, which is then double bonded to a sulfur.
- Thione: Thiones have a central carbon single bonded to two organic groups and double bonded to one sulfur.
- Thial: Thials are much like thiones, except that one of the thione's organic groups would be replaced with a single hydrogen atom.
- Thioester: Thioesters are the product of esterification between a carboxylic acid and a thiol. They feature an oxygen double bonded to a carbon. The carbon is then single bonded to a hydrogen atom or organic group. The carbon is also single bonded to a sulfur, which is then single bonded to another organic group or hydrogen atom.
These are functional groups that contain phosphorus bonded in some way to an organic group. Just as sulfur is the heavier analogue to oxygen, phosphorus is a heavier analogue to nitrogen, and has more unique bonding options available than the nitrogen based groups.
- Phosphine: Phosphines feature a central phosphorus single bonded to three groups that can either be organic groups or hydrogen atoms. In order to be considered an organic functional group, at least one of the single bonded groups must be an organic group.
- Phosphonic Acid: These acids are formed when a central phosphorus is double bonded to a single oxygen atom and single bonded to two hydroxyl groups and an organic group.
- Phosphate: Phosphates are almost identical to phosponic acids. Where the phosphorus is bonded to an organic group in a phosphonic acid, it is single bonded to an oxygen, which is then single bonded to an organic group.
- Phosphodiester: Phosphodiesters feature phosphorus bonded to four oxygen atoms. One of the oxygen atoms is attached via double bond and has no other bonds while one is singled bonded and part of a hydroxyl group. The remaining two oxygen atoms are also single bonded to the phosphorus, but are also single bonded to either two organic groups or one organic group and one hydrogen.
Functional groups containing boron are unique, in that they have partially filled octets and act as Lewis acids. This means that they are capable of forming reversible covalent complexes with sugars, amino acids, hydroxamic acids, molecules containing vicinal, or occasionally alcohols, amines, or carboxyalte.
- Boronic Acid: Boronic acid features a central boron atom single bonded to two hydroxyl groups and the carbon of an organic group.
- Boronic Ester: Boronic esters are boronic acids that have had the two hydroxyl groups replaced with oxygen atoms bonded to organic groups.
- Borinic Acid: Borinic acids feature a central boron atom single bonded to a hydroxyl group and two organic groups.
- Borinic Ester: Borinic esters are borinic acids with the single hydroxyl group replaced by an oxygen atom bonded to an orgnaic group.