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# Functional Groups

On the basis of the presence of carbon atoms, chemical molecules can be classified into two types; organic and inorganic molecules. Organic molecules are mainly composed of carbon atoms with some other atoms such as hydrogen or oxygen atoms. For example; the compounds which are composed of carbon and hydrogen only are known as hydrocarbons. Hydrocarbons are non-polar molecules as the electro negativities of carbon and hydrogen atoms are almost same.

One of the most common examples of hydrocarbons is alkanes which are saturated hydrocarbons with all single covalent bonds between carbon atoms. If any halogen group replaces one of the hydrogen atoms of alkane molecule, it becomes polar in nature. This is because of the presence of the halogen group in the molecule which is more electronegative compared to carbon and hydrogen atom. The presence of the halogen group changes the chemical and physical properties of alkane. In other words, it changes the functionality of the molecule. Such groups are called as ‘FUNCTIONAL GROUP’

### Define Functional Group

"A group of atoms or small groups of atoms which show a characteristic reactivity when treated with certain reagents and impart some characteristic chemical and physical properties to the main molecule is termed as functional group."

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## Organic Functional Groups

Some of the functional groups are mainly used in identification of organic compounds and their properties , so called as organic functional groups. According the IUPAC system, each functional group has characteristic names that often carry over in the naming of individual compounds incorporating specific groups.

For example,

When But-2-ene reacted with bromine in the presence of carbon tetrachloride, it forms 1,2-dibromobutane.
Both reactant and product show different properties, no doubt the have same number of carbon atom. But-2-ene gives additional reaction due to presence of double bond in the molecule, while 1, 2-dibromobutane can give substitution reaction as there is no double in molecule. So here double bonded carbon atoms and bromine is act as functional group.

Other example of functional groups are a carboxylic acid (RCOO-) and a ester (RCOOR) which is composed of an alkoxy group (-OR') and an acyl group (RCO-). In the nomenclature of organic compounds the combination of the names of functional groups with the names of the parent alkanes generates a systematic nomenclature.There are covalent bonds between different atoms of a functional group and these group attached to parent chain through covalent bond only. If there is a net charge on the group of covalently bound atoms it is referred as a polyatomic ion or a complexion.

The carbon atoms in a molecule can be positioned according to the position of attached functional group. The carbon just after the carbon that attaches to the functional group is known as alpha carbon while the second carbon atom termed as beta carbon and the third one as gamma carbon, etc.

If there is another functional group at a carbon, it may be named with the Greek letter, e.g., the gamma-amine in gamma-amino-butanoic acid is on the third carbon of the carbon chain attached to the carboxylic acid group.

### Common Functional Groups

Some of groups are very common in various organic compounds like hydroxy group, halo group, alkene and alkyne. Some other functional groups are as follows,

 Group formula Class name Example IUPAC name Common name Alkene CH2=CH2 Ethene Ethylene Alkyne CHâ‰¡CH Ethyne Acetylene Arene C6H6 Benzene Benzene -OH Alcohol CH3OH Methanol Wood alcohol -Cl Chloro CH3Cl Chloromathane Methyl chloride

### List of Functional Groups

There are some common functional groups listed in the following table with their structure. Carbon functional groups are very common in different organic compounds.

Some functional group form single bonds with hetero atoms like iodine, oxygen, nitrogen and sulfur. There are some other functional groups which have multiple Bonds with hetero atoms like oxygen and nitrogen atoms also.

 Group Formula Class name Specific example IUPAC name Common name Halide CH3-I Iodomethane Methyl iodide Alcohol CH3-CH2-OH Ethanol Ethyl alcohol Ether CH3-CH2-O-CH2-CH3 Diethyl ether Ether Amine CH3-NH2 Aminomethane Methyl amine Nitro compound CH3-NO2 Nitromethane Thiol CH3-SH Methane thiol Methyl mer captan Sulfide CH3-S-CH3 Dimethyl sulfide Nitrile CH3-CN Ethanenitrile Acetonitrile Aldehyde CH3-CHO Ethane Acetaldehyde Ketone CH3-CO-CH3 Propanone Acetone Carboxylic acid CH3-COOH Ethanoic acid Acetic acid Ester CH3-CO2-CH2-CH3 Ethyl ethanoate Ethyl acetate Acid halide CH3-CO-Cl Ethanoyl chloride Acetyl chloride Amide CH3-CO-N(CH3)2 N,N-Dimethylethanamide N,N-Dimethylacetamide Acid anhydride (CH3CO)2O Ethanoic anhydride Acetic anhydride

## Functional Groups of Amino Acids

Amino acids are building block of proteins. Amino acids form peptide linkage with each other to form protein through condensation polymerization with the elimination of water molecule.

Each amino acid consists of two functional groups; amino group (-NH2) and carboxyl group (-COOH) on same carbon atom. Since amino group is basic in nature and carboxyl group is acidic in nature, hence they cancel the effect of each other and make the molecule of neutral.

The carbon which is covalently bonded with both functional groups is termed as alpha-carbon atom.
Hence the presence of amino group and carboxyl group on same carbon atom is called an amino acid function group.

Hence we can identify different functional group in any organic compound. For example, in the given compound there are nitro, amide, ketonic and ether functional groups are present.

While in this compound there are two carbon containing functional groups are present that is aldehyde and alkene.

## Alkene Functional Group

If there is at least one double covalent bond between two carbon atoms, it termed as alkene group.
>C=C<
Remember that each carbon has four electrons in its valence shell, so for getting the octet configuration carbon has to form four covalent bonds with other or same atoms, in other words valency of carbon is four. If out of four bonds carbon forms two covalent bonds with another carbon atom, it called as alkene function group.

The presence of double covalent bond in a parent molecule makes the unsaturated and such type of organic compounds show additional reaction. For example; alkene can decolurise the brown color of bromine water due to the formation of dibromoalkane.
>C=C< + Br2 $\to$ >C-C<
l l
Br Br

## Alcohol Functional Group

Those organic compounds which have hydroxyl group (-OH) as a main functional group; is called as alcohol function group. The presence of hydroxyl group make alcohol different molecule from other organic compounds.

There are two lain pairs of electron on oxygen atom which involves in different chemical reactions of alcohol and responsible for the formation of hydrogen bonds with other molecules of alcohol as well as with water.
Hence, the hydroxyl group is an alcoholic functional group.

The bond angle of oxygen hydrogen bond is 108A$\degree$ which is very close to tetrahedral bond angle (109A°28). For example; methanol consist one hydroxyl group with one methyl group.

## Hydroxyl Functional Group

In organic chemistry the hydroxyl group is define as the functional group in alcohols also being a part of other organic chemical structure like natural products, drugs, and present in some biochemical structureâ€”in sugars and in some amino acids like threonine and phospholipids. Hence hydroxyl group acts as biological barriers such as bio-membranes and cell walls.

This functional group involve in various organic synthesis, enzyme catalysis as well as in inhibition, and in the formation of biological structures, due to its hydrogen bonding capability.

The ability of formation of hydrogen bonding makes hydroxyl group as a part of protein-ligand interactions, and imparts water solubility and internal structural stability to macromolecules, etc.

## Nitrogen Functional Groups

There are many functional groups with nitrogen atom. Mainly there are two category of functional groups; amine and amide functional group.
Amines can be four different types on the basis of alkyl groups and hydrogen bonded with nitrogen atom of amine.
• R-NH2 Primary Amines
• R-NH-R' Secondary Amines
• R-N(R)-R' Tertiary Amines
• N(R)4+ Quaternary Amines .
All amines are basic in nature and react with water to form basic solutions which have bitter taste and feel slippery. Due to basic nature of solution and turns litmus blue and react with acids to form salts. However Compounds Carbon -Oxygen bonds with nitrogen atom is called as amides.
There are many other functional groups also with nitrogen atom; like nitro (-NO2), Cyano (-CN), isocyano (-NC) , nitrite (-ONO) ,imine , imide , azide , cyanat and azo group in azo compounds.

Some common functional groups with structure and name as follows;

 Chemical class Group Formula Structural Formula Example Amide Carboxamide RCONR2 Acetamide (Ethanamide) Amines Primary amine RNH2 Methylamine (Methanamine) Secondary amine R2NH Dimethylamine Tertiary amine R3N Trimethylamine Quaternary ammonium ion R4N+ Choline Imine Primary ketimine RC(=NH)R' Secondary ketimine RC(=NR)R' Primary aldimine RC(=NH)H Secondary aldimine RC(=NR')H Imide Imide (RCO)2NR' Azide Azide RN3 Phenyl azide (Azidobenzene) Azo compound Azo (Diimide) RN2R' Methyl orange (p-dimethylamino-azobenzenesulfonic acid) Cyanats Cyanate ROCN Methyl cyanate Isocyanate RNCO Methyl isocyanate Nitrate Nitrate RONO2 Amyl nitrate (1-nitrooxypentane) Nitrile Nitrile RCN Benzonitrile (Phenyl cyanide) Isonitrile RNC Methyl isocyanide Nitrite Nitrosooxy RONO Isoamyl nitrite (3-methyl-1-nitrosooxybutane) Nitro compound Nitro RNO2 Nitromethane Nitroso compound Nitroso RNO Nitrosobenzene Pyridine derivative Pyridyl RC5H4N Nicotine

## NH2 Functional Group

NH2 functional group is also termed as amino or amine group. Amine group obtained after the replacement of one hydrogen atom of ammonia by an alkyl or aryl group. This is also known as primary amine group. It can be two type;
• Aliphatic R-NH2
• Aromatic Ar-NH2
Amine group is basic in nature due to the presence of lain pair on the nitrogen atom.

COOH Functional Group

COOH group is also called as carboxyl group, which show acidic nature due to the presence of OH group.

Carboxyl functional group is a combination of a carbonyl group (>C=O) and a hydroxyl (-O-H). No doubt it physical and chemical properties are quite different from both groups. Due to the presence of carbonyl group, the hydroxyl group in carboxyl group shoe acidic nature.

The fourth valency of carbon atom of carboxyl group can be satisfied with alkyl or aryl group. If there is a alkyl carbon chain, it is termed as aliphatic carboxylic acid, while presence of aryl group with carboxyl group is formed aromatic carboxylic acid, also named as derivatives of benzoic acid.

Methyl Functional Group

Methyl group is a side chain or branch of the main parent chain in an organic compound. It acts as a substituent with main parent carbon chain.

Branching with main parent chain effect the physical as well as chemical properties of organic compounds. Its mainly effect the melting point, boiling point and surface area of compound.

## Phosphate Functional Group

Phosphate group is an example of that functional group in which there is multiple bonds with hetero atom like phosphorus. In phosphate functional group one of the oxygen atoms bonded with phosphorus atom as well as one alkyl group.

This functional group present in organic phosphates and make them acidic in nature. The common example of organic compounds with phosphate group is adenosine triphosphate (ATP) and DNA, phosphoric acid (H3PO4 ), phosphorus acid (H3PO3 ) etc.

Some other functional groups with hetero atom as phosphorus are as follow;

 Class Group Formula Structural Formula Example Phosphine(Phosphane) Phosphine $R_3$P Phosphonic acid Phosphono RP(=O)$(OH)_2$ Phosphodiester Phosphate HOPO$(OR)_2$ o-[(2-Guanidinoethoxy)hydroxyphosphoryl]-L-Serine            (Prefix)          (Lombricine)

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