Functional Groups – Everything on the topic

You may be familiar with the fact that small changes in your environment can change you and your mood. According to the same principle, small structural changes can also cause changes in molecules. These small structural changes were then classified and called functional groups.

functional groups are individual groups of atomic compositions in organic compounds, which can change the original molecule enormously in areas of material properties and reaction behavior. The groups into which the functional groups are divided are called substance classes.

Overview of the functional groups

In total there are over 50 functional groups and one C atom can bind a maximum of four functional groups. These can first be divided into «compounds with heteroatoms» and «compounds without heteroatoms». heteroatoms are simply all atoms except carbon atoms. A “compound without heteroatoms” is therefore a carbon chain, which possesses a double or triple bond between these carbon atoms but contains no other atoms.

The «compounds without heteroatoms» are often not considered as real functional groups because they only represent a structural feature and do not contain any additional atoms.

You can also go to alkyl or aryl groups and organyl groups differentiate. The alkyl and aryl groups only occur in inorganic or organometallic compounds. All other organic functional groups are called organyl groups. These have the highest proportion of functional groups.

List of functional groups

Here you have a short overview of the most important functional groups. In the first two lines you can see the already mentioned compounds without heteroatoms. The remainder are all organyl groups.

substance class

functional group

example

Surname

semi-structural formula

designation

Surname

structural formula

alcohols

hydroxy group

RAW

-oil

eg ethanol

C2H5OH

Halocarbons

halide

-F-Cl-Br-I

Halogen-

eg monobromoethane

C2H5Br

amines

amino group

R-NH2

-amine

eg ethylamine

C2H5NH2

ether

ether group

R1-O-R2

-ether

eg diethyl ether

(C2H5)2O

aldehydes

aldehyde group

R-COH

-al

eg ethanol

CH3CHO

ketones

keto group

R1-CO-R2

-on

eg propan-2-one

(CH3)2CO

carboxylic acid

carboxy group

R-COOH

-acid

eg acetic acid

CH3COOH

ester

ester group

R-COOR

-ester

eg methyl ethanoate

CH3COOCH3

Structural formulas of the functional groups

As you already know, the basic structure of an organic molecule is always a carbon atom chain. Any desired functional group can bind to each carbon atom.

There are also differences in the functional groups due to their location and the bonds they have formed.

A distinction can be made between primary, secondary and tertiary functional groups. In fact, which of the groups it is does not depend on the functional group itself, but on the carbon atom to which it is attached. In addition you have to check whether the carbon atom to which your functional group is attached has one, two or more residues.

A «radical» is a bond to atoms other than hydrogen. It doesn’t matter how big the rest is, i.e. how many other atoms are bound there.

If a radical and two hydrogen atoms are attached to the C atom, then it is one primary functional group. If two groups and one hydrogen atom are attached to the carbon atom, it is one secondary functional group. And if only residues and no H atom are bonded to the carbon, then there is one tertiary functional group.

If, for example, an alcohol is bonded to a carbon atom that is only bonded to hydrogen atoms apart from the alcohol group, then you have a primary functional group, i.e. a primary alcohol in this case.

Properties of the functional groups

The functional group influences the properties of the chemical compounds. Both melting and boiling point, solubility and volatility are determined by the functional group. Reactivity and reaction possibilities are also defined by the functional group. This can be illustrated using the example of the alkane n-butane and the other modifications.

functional group

connection

structural formula

Characteristics

n-butane

H3C-CH2-CH2-CH3

gaseous

carboxy group

butanoic acid (butyric acid)

H3C-CH2-CH2-COOH

Liquid, foul-smelling, has an acidic reaction

amino group

butane-2-amine

H3C-CH(NH2)-CH2-CH3

Liquid, foul-smelling, has a basic reaction

In addition to the functional group, however, the length and structure of the molecular residue also play a role in the Strength of the properties that occur. You can also convert one functional group into another functional group through chemical reactions. By a reduction one carboxyl group leaves reach, for example, a hydroxyl group.

Functional group naming

Based on the endings or whole word parts of the name of a molecule, you can already see which functional groups this molecule contains. Most of the time, the functional groups have either a prefix or a suffix that is simply appended to the original name of the molecule.

This is best explained with an example. Assume you have the organic compound of propane as the backbone. Propane has a five-carbon chain. Without any functional group it is simply a propane. However, if an alcohol is attached to the third atom, then you have a PropanOL, because the specific suffix for alcohols (-OH) is the two letters -ol. In the case of an ethane with an alcohol group, this would then be called ethanol.

However, when multiple groups are attached to a carbon chain, things get a little more complicated.

But exactly for this case there are the so-called priority rules. The priority rules are as follows: The designation always follows the function group with the highest priority. The priority is in the table below sorted in descending order. If the molecule contains the carboxyl group COOH, then it must be a carboxylic acid with the suffix -acid, even if other functional groups are present in the molecule. These then receive the corresponding prefix.

If you would like to take a closer look at the naming, then have a look at the IUPAC nomenclature article.

structure

substance group

ending

prefix

examples

R-COOH

carboxylic acid

-acid

carboxy

acetic acid

R-CO-H

aldehyde

-al

oxo

ethanal

R1-CO-R2

ketone

-on

oxo

propanone

RAW

alcohol

-oil

hydroxy

ethanol

R-NH2

amine

-amine

amino

methylamine

R1-O-R2

ether

-ether

R2yloxy

diethyl ether

Functional group examples

Below you can take a closer look at a few important examples of molecules with functional groups.

The functional group of alcohols

the alcohols belong to the hydroxy group and thus to the functional group with the heteroatoms. An alcohol gets its name from the basic structure of the corresponding alkane and the suffix -ol. The name of the alcohol with a butane skeleton is butanol. The is important for the properties of the substances polarization.

For the following part of the explanation you should know that the electronegativity of an atom indicates how strongly it attracts electrons within a bond. When one atom shares an electron with another through a bond, that electron can be at different distances from the atomic nuclei. This determines the electronegativity.

If the value of electronegativity is large, then the attraction of electrons is very strong.

And the higher the difference in the electronegativity of the bound elements, the the bond is more polar

If you want more information on this, have a look at the explanations of electronegativity and polarity.

The hydroxy group is one of the polar atomic groups, which is why a negative charge center forms on the oxygen atom and a positive charge center forms on the carbon atom/hydrogen atom. Because of this, hydrogen bonds form, for example, the liquid state and the water solubility of alcohols justify.

Take a look at the explanation for alcohols!

The functional group of the carboxylic acid

The carboxylic acid belongs to the functional group of carboxyl group. The carboxylic acids are named for the basic structure with the suffix «-acid». That is the chemical name of the formic acid, formic acid.

the carboxyl group can release an H+ ion, which is why the compound can have high acidity. In addition, the carboxyl group also a high one polarity and thus a high boiling and melting point. The carboxylic acids also dissolve well in water.

You can find more details about the carboxylic acid in its explanation!

The functional group of the aldehydes

The functional group of aldehydes is the carbonyl group. The name of this group is also made up of the basic skeleton of the alkane and the suffix -al. The aldehyde with the basic skeleton methane is accordingly methanal. This is often also referred to as formaldehyde.

Like the hydroxy group, the carbonyl group polar. The melting and boiling points of the aldehydes are, however, slightly lower than those of alcohols, since the polarity is somewhat weaker. As the alcohols are those too aldehydes hydrophilic.

Here, too, there is an explanation of the aldehydes, which provides you with additional information!

Functional Groups – The Most Important

  • There are over 50 functional groups.
  • Functional groups are compounds on organic molecules that can change the state, material properties and reaction behavior of the molecule.
  • Depending on how many radicals are attached to the carbon of the functional group, it is a primary, secondary or tertiary group.
  • Functional groups can already be recognized from the molecule name by the initial syllable or the suffix.

proof

  1. chemie.de: Functional group (07/22/2022)
  2. schule-bw.de Overview: Functional groups (07/23/2022)
  3. Seilnacht.com: Nomenclature of organic chemistry (07/23/2022)