Organic Definitions  

Vital Force Theory

This theory was proposed by J. J. Berzellius.

According to this theory, organic compounds could be manufactured only by and within living things and these compounds could never be synthesized from inorganic materials as these compounds required vital force for their synstheis.

Organic Chemistry

The study of covalent compounds of carbon containing H, and often O, N, S, P and halogens (Cl, Br and I) containing C – C bond is termed as Organic Chemistry.

OR

The study of hydrocarbons and their derivatives is called Organic Chemistry.

Catenation (a unique property of carbon)

One of the remarkable property of carbon atom is its unique capacity to form bonds with other carbon atoms. This property of forming bonds with atoms of the same element is called catenation. The property of carbon atoms to bond or link itself to other carbon atoms forming long chains, branched chains, rings or compounds with chains and rings together is called Catenation. It is property of self-linking of carbon atoms through covalent bonds to form long straight or branched chains and rings of different sizes.

Alkyl Radicals                   

Alkyl groups are the basic structural unit of all aliphatic organic compounds. The residual hydrocarbon group or radical left after the removal of a hydrogen atom from a saturated hydrocarbon alkane is called an alkyl group or radical. Stated differently, the radicals obtained from alkanes by the removal of one hydrogen atom are called alkyl group or radical. They are generally represented by ‘R–‘. 

Aryl  Radical                                                      

Aryl groups are the basic structural unit of all aromatic organic compounds. The residual hydrocarbon group or radical left after the removal of a hydrogen atom from arenes or aromatic compounds is called an aryl group or radical. Stated differently, the radicals obtained from arenes by the removal of one hydrogen atom are called aryl group or radical. They are generally represented by ‘Ar–’.

1° or primary carbon atoms

A carbon atom either alone or attached to not more than one other carbon atom is called primary carbon denoted by 1° or p.

2° or secondary carbon atoms

A carbon atom which is attached to two other carbon atoms is called secondary carbon denoted by 2° or s.

3° or tertiary carbon atoms

A carbon atom which is attached to three other carbon atoms is called tertiary carbon denoted by 3° or t.

Quaternary carbon atoms

A carbon atom which is attached to four other carbon atoms is called tertiary carbon denoted by 4° or q.

Homologous Series

“The members of the same class of organic compounds arranged in order of ascending molecular masses having same functional group whose successive members differ from each other by an integral number of methylene groups (–CH₂–) in their molecular formulae (or by molecular mass of 14) are said to form a Homologous Series.”

                                                            OR

A set or series or group of structurally similar organic compounds in the increasing order of carbon atoms having same elements, same functional group, same general formula and identical chemical properties, show a gradation in physical properties, and any two adjacent members of which differ by –CH₂– units (methylene groups) is called Homologous Series. The individual members of the series are called HOMOLOGUES and the phenomenon itself is called HOMOLOGY.

Functional Group

An atom or group of atoms whose presence confers on organic molecule characteristics properties unique to that group is called Functional Group. It is the site of chemical reactivity of organic compounds.

OR

An atom or group of atoms which is present within the organic molecule and is responsible for its chemical behaviour and characteristic properties is called Functional Group.

Aliphatic Compounds

The organic compounds whose molecules are composed of open chains of carbon atoms either branched or unbranched are called Acyclic Compounds. They are commonly called Aliphatic Compounds (Greek word; means oil-fats characteristics) as some of the important members are found in fats.

 

Saturated aliphatic Compounds

Saturated aliphatic compounds (H.C.) have the structure in which all the four valencies of a carbon  atom are fully satisfied by forming four sigma bonds with four other atoms (usually hydrogen) 

Unsaturated aliphatic compounds

Unsaturated aliphatic compounds have the structure in which all the four valencies of carbon atom are not filled completely and one or more valencies are used in forming multiple (pi) bonds. 

Cyclic or Ring Compounds

Compounds whose molecules are composed of closed chains or rings of carbon atoms (with or without atom of other elements) are called Cyclic Compounds. Cyclic compounds are further divided into two types:

Heterocyclic Compounds

The cyclic compounds having one or more hetero atoms (like nitrogen, sulphur or oxygen) along with carbon in the ring are called Heterocyclic or Non-Carbocyclic Compounds. More or less 3600 heterocylic compounds are known. The various different prefixes are used to indicate the kind and number of hetero atoms. e.g.

Homocyclic Compounds

These are the cyclic compounds in which the main skeleton or ring is made up of carbon atoms only. Homocyclic compounds are further divided into two groups:

Alicyclic Compounds

They are carbocyclic or homocyclic compounds which do not contain any benzene ring. They resemble aliphatic compounds in many ways. They are homocyclic organic compounds which contain a ring of three or more carbon atoms (other than benzene ring) resembling aliphatic compounds. They may be saturated or unsaturated. They have general formula C_nH_2n or C_nH_2n–2

Aromatic Compounds

Aromatic compounds are benzenoid homocyclic (or carbocyclic) compounds containing one or more benzene rings (which is a hexagonal ring of six carbon atoms with three alternating double and single bonds) in their molecules. Aromatic compounds and their derivatives have characteristic smell. The pungency (fragrant odour or aroma) of benzene gives rise to the name aromatic (Greek, arome = smell) for all the members of the class (even though many are odourless).

Isomerism

The word isomer is a combination of two words, iso means same and mers means unit and this term was invented by Berzelius. The compounds which differ in their properties but have same molecular formula are called isomers and the phenomenon is known as isomerism.

Isomerism is the existence of different compounds exhibiting different physical or chemical properties or both having same molecular formula i.e. The phenomenon of existence of two or more compounds possessing the same molecular formula but different properties is known as isomerism. Such compounds are called as isomers.

Isomers refer to those compounds which have the same molecular formula but differ in physical or chemical properties or both i.e. Isomers have entirely different physical properties and in many cases also have distantly different chemical properties (except chain isomers, metamers).

Structural or Constitutional Isomerism

When isomerism is caused by the difference in the arrangement of atoms or group of atoms within molecule without any reference to space is called Structural or Constitutional Isomerism. Structural or Constitutional Isomers are compounds that have same molecular formula but different structural formulae due to different arrangement of atoms or groups or multiple bonds. Structural Isomers have entirely different physical and in most cases also have distantly different chemical properties. In this type of isomerism, compounds possessing same molecular formula differ in their properties due to the difference in the linkages of atoms or groups inside the molecule i.e. due to the difference in their structures. The constitutional isomers differ in the connectivity of carbon atoms i.e. differ in their structural formulae.

Stereoisomerism

The prefix stereo- is derived from the Greek word stereos meaning solid. When isomerism is caused by the different spatial configuration (i.e. three-dimensional arrangement) of atoms or groups in space is called Stereoisomerism. Stereoisomers have same molecular formula and also the same structural formula but differ in arrangement of the bonds (atoms) in space. Stereochemistry is the term applied to the three-dimensional aspects of molecular structure and reactivity. Stereoisomerism is of three types: 

Chain or skeletal or nuclear isomerism

Isomerism resulting from varying configuration of main carbon skeleton or chain is called skeletal or nuclear isomerism.

Different compounds which have same molecular formula but they differ in the configuration of their main carbon skeleton or chains having different carbon chains are called chain or skeletal isomers.

In this type of isomerism, compounds possessing same molecular formula differ in their properties due to the difference in the arrangement of carbon chain i.e. branched or unbranched chain present in them. Here a chain of minimum 4 carbon atoms is necessary to show this type of isomerism.  

Position Isomerism

Isomerism resulting from varying position of the functional group in the same carbon skeleton is called positional isomerism.

Different compounds that have same molecular formula but their structural formulae are different due to different position of functional group or multiple bonds in the same carbon chain are called positional isomers. Aldehydes, carboxylic acid and their derivatives do not exhibit position isomerism

Functional Group Isomerism/ Functional Isomerism

Isomerism resulting from the presence of different functional group is called functional isomerism. Different compounds which have same molecular formula but their structural formulae are different due to the presence of  different functional groups are called functional group isomers/ functional isomers.

Ring chain Isomerism

Here is isomers mode of chain formation differs i.e. open or close type of chain formation. Ring chain isomers are also functional isomers. In this type of isomerism compounds are having same molecular formula but differ in modes of linking of carbon atoms, i.e. it may either be open chain or closed chain structures.

Metamerism

Isomerism resulting from unequal distribution of carbon atoms (alkyl or aryl groups) on either side of the polyvalent functional group is called metamerism.

Different compounds which have same molecular formula having same functional group in which polyvalent atom of the same functional group joins different combinations of alkyl or aryl radicals are called metamers. 

It is the type of isomerism in which compounds possessing same molecular formula differ in their properties due to the difference in the alkyl groups present in them i.e. same functional group but different alkyl groups attached to it. It is a type of chain isomerism.

Tautomerism or Keto-enol Isomerism(Greek word : tauto = same ; meros = parts)

 It was used by Laar in 1885. Tautomerism is a special case of functional group isomerism arises when two isomers are in dynamic equilibrium. In other words, tautomerism is a process by which two isomers are dynamically interconverted by an actual or formal movement of an atom or a group. Keto-enol isomerism or enolization is a form of tautomerism by which an aldehyde or a ketone and its enol equilibrate. Tautomerism may be defined as the phenomenon in which a single compounds exists in two readily inter convertible structures that differ markedly in the relative position of at least one atomic nucleus generally hydrogen. The two different structures are known as tautomers of each other.

In tautomerism, two isomeric forms of a compound (aldehyde or ketone) exist in dynamic equilibrium. Thus tautomerism refers to an interconversion between two structures that differ by the placement of an atom or a group. The tautomers differ in the position of a hydrogen atom. 

 

Electrophiles OR Electrophilic Reagents

A chemical reagent which can accept an electron pair in a reaction is called an electrophile. Thus they act as electron pair acceptor during a reaction. They attack on the negative centre of the molecules and love electrons. They are represented by E⁺.

The name electrophile means “electron-loving” which indicates that an electrophile always attacks regions of high electron density (negative centers) in the substrate molecule due to deficiency of electrons.

They are also called Lewis Acid as they are electron-deficient species and hence have an affinity for electrons.

 

nucleophiles or Nucleophilic Reagents

 A chemical reagent which can donate an electron pair in a reaction to an electron deficient part to make a new covalent bond is called a nucleophile. They attack on the positive site of the substrate molecule or loves electron. Thus they act as an electron pair donor during a reaction. They are represented by N^‾ or Nu^‾.

 The name nucleophile means “nucleus-loving” which indicates that a nucleophile always attacks regions of low electron density (positive centers) in the substrate molecule due to sufficiency of electrons.

They are also called Lewis Base as they are electron-rich species and hence have an affinity for positive nucleus.

 

Cracking or Pyrolysis

The thermal decomposition of larger long chain less volatile (high-boiling) saturated hydrocarbons (alkanes) of higher molecular weight into a mixture of lighter or smaller, more volatile (low-boiling) alkanes, alkenes and hydrogen in the absence of air on heating well above their boiling points (400-800°C) with or without catalyst is called Cracking or Pyrolysis.

It is the process of splitting the larger molecules of less volatile fractions into smaller molecules of higher volatile fractions by subjecting them to high temperature and pressure in the presence of catalyst and in the absence of air. It is the process of decomposition of less volatile hydrocarbon into more volatile by heating.

 

Polymerization

Polymerization is a combination of two words; Poly means many and mero means unit or part.

It is the process in which a large number of smaller molecules of low molecular weight unite to form a single new larger molecule of higher molecular weight. 

OR

It is a chemical reaction in which a large number of smaller molecules called monomers react together to form a larger molecule called polymer that contains repeating structural units. The macromolecules formed may have a linear or branched structure with complex three-dimensional network.

Addition/chain growth polymerization

It involves the addition or self-combination of unsaturated monomers of same compound to form longchains, branched or unbranched and cyclic structures of polymer with a molecular mass many times                 greater than the monomers without removal of water molecule.

It proceeds without the elimination of small molecules like H₂O, HCl, CH₃OH etc.

Condensation Polymerization

It involves the addition of two different types of monomers which are condensed into new bond between units by the removal of water or NH₃ or HCl.

When large number of different smaller molecules combine together to form a big molecule with theelimination of one small molecule is called condensation polymerization.

Natural condensation polymers are proteins, cellulose, glycogen etc.

Synthetic condensation polymers are nylon, polyesters and polyamides.

 

Carbonization or Destructive Distillation

Thermal decomposition of a highly carbonaceous material such as coal in the absence of air resulting in decomposition to solids, liquids and gases is called Carbonization or Destructive Distillation. The process is called carbonization as the solid end product is carbon.

Knocking or Pinking or Pinging

A sharp metallic sound or tapping noise produced in the internal combustion engine due to pre-ignition or premature combustion of the fuel in the cylinder prior to sparking is called Knocking or Pinking. (Lead compounds in car exhaust gases are becoming a health hazard when ingested in only moderate quantities, it makes peoples depressed and increases their reaction time)

Octane Number or Octane Rating

Gasoline or petrol is a complex mixture of C₅-C₁₀ alkanes along with varying amounts of aromatic hydrocarbons. Different gasolines vary in respect of their knock property depending on their composition. Fuel value of gasoline or petrol is expressed by a rating called Octane Number or Octane Scale determined by experiment, which is a measure of its resistance to knocking. It is the unit for the quality of fuel like petrol. Gasolines with high octane number burn more smoothly and are thus more effective fuels.

Reforming (Isomerisation) of Petroleum

The process in which the atoms are rearranged in straight chain alkanes (obtained from gasoline fractions) to produce branched chain alkanes or aromatic hydrocarbons is known as Reforming or Isomerisation. It is the conversion of straight hydrocarbon into branched chain hydrocarbons in order to increase the octane number of a fuel to avoid knocking.

 

Carbohydrates

Carbohydrates are natural macromolecules including a large number of relatively heterogenous compounds containing C, H and O and are the most abundant biomolecules on the earth. They are commonly called sugars or saccharides (Latin; saccharum meaning sugar).

 

Carbohydrates are defined as the polyhydroxy aldehydes (polyhydric aldehydes) or polyhydroxy ketones (polyhydric ketones) or the compounds (large polymeric compounds) that yield units of such compounds (i.e. polyhydroxy aldehydes or ketones) upon hydrolysis. These are polyhydroxy compounds containing aldehydic or Ketonic functional group either free or as heciacetal or acetal form.

Carbohydrates are regarded as the Hydrates of Carbon because the ratio of O and H as same as it is in water (i.e. in the ratio of 2:1). Their general formula is C_x(H₂O)_y.

Reducing Sugars

Reducing Sugars are those sugars that contain free aldehydic or ketonic group (along with adjacent –OH group) and they can reduce mild oxidizing agents like Benedict’s reagent [alkaline solution of citrate complex of copper (II)], Fehling’s Solution [alkaline solution of tartarate complex of copper (II)] or Tollen’s reagent [ammonical silver nitrate solution]. All monosaccharides and all disaccharides except sucrose are reducing sugars. e.g. glucose, galactose, fructose, maltose, lactose.

Non-reducing sugars

Non-reducing Sugars are those sugars, which lack free aldehydic or ketonic group, and they cannot reduce mild oxidizing agents like Benedict’s reagent, Fehling’s Solution or Tollen’s reagent.

Examples

One disaccharide (e.g. Sucrose) and all polysaccharides (e.g. starch, cellulose etc.) are non-reducing sugars.

Monosaccharides/Simple Sugars/ Non-Hydrolyzable Sugars 

These are the simplest carbohydrates and are non-hydrolyzable simple sugars that cannot be further hydrolyzed into simpler carbohydrate units consisting of aldoses or ketoses. They contain 3-10 carbon atoms.

Oligosaccharides (Hydrolyzable Sugars)

These are carbohydrates which are formed when 2-10 (2-9 in reality) monosaccharide units condensed together through glycosidic linkage by the loss of water molecule.

Conversely the carbohydrates which give 2-10 (2-9 in fact) simple sugar (monosaccharide) units on hydrolysis by water (in the presence of an acid or by enzymes) are called oligosaccharides.

Disaccharides

Disaccharide is formed by the joining (condensation) of two molecules of same or different monosaccharides units through glycosidic linkage by giving out a water molecule and thus on hydrolysis disaccharide yield two units of simple sugars. They are commonly known as saccharose

Polysaccharides(Tasteless,Amorphous, Hydrolyzable Non-Sugars)

Polysaccharides are carbohydrates of high molecular mass that yield more than 10 monosaccharides units upon hydrolysis and are made up of long chains of many monosaccharides units joined to each other through glycosidic linkage in a linear or branched structure by the process of polymerization.

D-Sugars

All sugars in which –OH group on penultimate carbon atom is on right hand side are called D-Sugars. .e.g.   D-glucose

L-Sugars

All sugars in which –OH group on penultimate carbon atom is on left hand side are called L-Sugars. e.g.  L-glucose

Dextrorotatory Sugars

The carbohydrates which rotates plane of polarized light from left to right is called Dextrorotatory. They are represented by (+). e.g. D-glucose

Levorotatory Sugars  

The carbohydrates which rotates plane of polarized light from right to left is called Levorotatory. They are represented by (-). e.g. L-glucose

Mutarotation

The property by which two isomeric close chain structures which are interconvert by open chain structures is called mutarotation.

Alpha-Isomer

It is the close chain structure of carbohydrates having OH group on carbon 1 is on right hand side or below plane.

 

β-Isomer

It is the close chain structure of carbohydrates having OH group on carbon 1 is on left hand side or above plane.

Glycosidic Linkage

Glycosidic bond is a covalent bond that holds a carbohydrate (sugar) to another functional group (-OR) or molecule that can or cannot be another sugar.

 

A Glycosidic Linkage is one in which a carbon atom is joined to two oxygen atoms through single bond (i.e. -O-C-O-) in carbohydrates. A glycoside is a compound that contains a glycoside bond.

Amino acids

Amino acids are the basic building blocks of proteins. Amino acids are bifunctional (polyfunctional) organic acids having both an acidic carboxyl group (-COOH) and a basic amino group (-NH₂ or >NH) along with distinct side chain R (which is different for different amino acids).

Essential Amino acids 

About 20 amino acids have been identified as the constituents of most of the animal and plant proteins.

 Out of 20 amino acids which are required for protein synthesis, the human body can synthesize only             10 and such amino acids are called Non-essential amino acids. e.g. Glycine, alinine, proline, aspartic acid, glutamic acid, tyrosine, serine, cysteine, aspargine.

Non-Essential Amino Acids

The ten amino acids that are not synthesized by human body and hence are needed to be provided in the diet for proper health and growth are called Essential Amino Acids.

They are 10 for infants and 8 for adult human being.

e.g. Valine, Leucine, Isoleucine, Lysine, Methionine, Threonine, Arginine, Tryptophan,           Phenylalanine, and Histidine (last two are needed for infants).

Neutral amino acids

They exhibit amphoteric nature. They contain one basic amino group and one acidic carboxylic group

Acidic amino acids

They exhibit acidic nature. They contain one basic amino group and more than one acidic carboxylic group

Basic amino acids

They exhibit basic nature.They contain one acidic carboxylic group and more than one basic amino groups.

Zwitterion

The dipolar charged but overall electrically neutral ion with positive as well as negative ends within the same molecule is termed as Zwitterion (German; two ions).

The dipolar ionic structure is also called internal salt.

 

All a–amino acids exist largely as dipolar ionic forms or Zwitterions in solution that is formed when the proton goes from the acidic carboxylic group (on ionization) to basic amino group (Lewis base). i.e. carboxylic group of amino acids ionizes to donate proton while its amino group with a lone pair of electrons acts as a proton acceptor (Lewis base) forming dipolar charged ion or Zwitter ion.

Peptide Linkage

The acid-amide (-CO-NH-) bond through which amino acids are linked in proteins by eliminating a water molecule is called Peptide Linkage.

This linkage is formed by the removal of a water molecule b/w an -NH₂ group of an amino acid and -COOH group of another.

 The product formed from condensation of two amino acids containing a single peptide linkage is  called Dipeptide.

The product formed from condensation of three amino acids containing two peptide bonds is called Tripeptide.

Proteins

All proteins yield amino acids which are generally a-amino carboxylic acids of different molecular sizes, upon complete hydrolysis. Thus, amino acids are the basic constructing units of proteins.

Proteins (derived from Proteios meaning first) are the complex nitrogenous long chains polymericorganic macromolecules of very high molecular weight (34,000-5,000,000 dalton or 17500-6,000,000 Da) which are giant linear condensation biopolymers of a-amino acid monomers (ranging from 200-6,0000) interlocked or linked together through peptide linkages (acid-amide bonds) through condensation polymerization or polycondensation with the elimination of water molecules.

 

Simple proteins

These are the simplest proteins which upon hydrolysis yield only amino acids and their derivatives. e.g. egg albumin, serum albumin of blood, and milk albumin (lactalbumin) etc.

 

Conjugated proteins

These are the proteins which consist of simple proteins with non-proteinous substance called prosthetic group. e.g. Haemoglobin, Chlorophyll.

 

Derived Proteins

These are not naturally occurring proteins and are obtained by degradation of proteins by acids, alkalis, heat, enzymes or biochemical action. e.g. peptones, proteoses, polypeptides, peptides.

Lipids

The lipids are a group of heterogenous, water-insoluble, non-polar organic compounds of the plant and animal origins which are soluble in Bloor’s reagent (a mixture of diethyl ether and ethyl alcohol in the ratio of 2:1)

Simple Lipids

The ester of glycerol with fatty acid is called simple lipid. e.g. fats, oils, waxes

Conjugated Lipids

The ester of glycerol with fatty acids and substance other than fatty acid is called compound lipids. e.g. phospholipids

Steroids

The non-saponifiable lipids which contains ring system is called steroid. Steroids are one of the various classes of lipids. e.g. cholesterol, cholic acid. Steroids are non-saponifiable fats.

Simple and Mixed Glycerides

When the three OH group of glycerol are esterified with the same acid, the triglyceride is known as Simple Glyceride (Simple Fat).

If two or more OH groups of glycerol are esterified with different fatty acids, then the triglyceride is known as Mixed Glyceride or Mixed triglycerides or Mixed triacylglycerols (Mixed Fats).

Cooking oils and fats are mixed triglycerides containing all the three different fatty acids.

Fat

The ester of glycerol with saturated fatty acid (palmitic acid) is called fat. Fats are solid state esters (triglycerides) of fatty acid and glycerol at room temperature containing a higher proportion of saturated fatty acids in their esters.

Oil

The ester of glycerol with unsaturated fatty acid (oleic acid) is called oil. Oils are liquids state esters (Triglycerides) of fatty acids and glycerol at room temperature containing a higher proportion of unsaturated fatty acids in their esters.

Waxes

The ester of long chain alcohols with long chain carboxylic acid (fatty acid) is called wax e.g. Bess wax, spermacetic wax  

Fatty acids 

Fatty acids are naturally occurring non-branched aliphatic monocarboxylic acids consisting of a long saturated or unsaturated hydrocarbon chain with a terminal carboxylic group mostly obtained from hydrolysis of natural fats and oils containing even number of carbon atoms (ranges C₁₂-C₂₀).

Essential Fatty acids

Essential Fatty acids are those fatty acids that our body cannot synthesize so they must be taken as diet. The function of essential fatty acids is:

All essential fatty acids are unsaturated i.e.:

i.          Linoleic acid           (C₁₇H₃₁-COOH)

ii.         Linolenic acid         (C₁₇H₂₉-COOH)

iii.         Arachidonic acid    (C₁₉H₃₁-COOH)

 

Saponification

The alkaline hydrolysis of fats or oils on boiling with a solution of strong alkali (NaOH or KOH) to form sodium or potassium salt of long chain fatty acid (soap) along with glycerol is called Saponification.

 It is the reverse process of esterification of glycerol.

Rancidification

The development of disagreeable foul smell and unpleasant bad taste in a fat or oil caused by its hydrolysis or oxidation on exposure to warm, moist air for a long time is called Rancidification or Rancidity.

 

Iodine Number

The degree of unsaturation of a fat or oil is usually measured by Iodine Number. It is the number of gram of iodine consumed or absorbed by 100 gram of fat or oils.

Vitamins

Vitamins are the complex organic compounds which act as a catalysts or promoters and facilitate the metabolic processes required in very small amount. They cannot be synthesized by the animals hence they must be supplied in diet.

enzymes  

The word enzyme has a Greek origin which means that “in the yeast”.

Enzymes are the class of proteins which are the complex polymeric nitrogenous organic biocatalysts produced by living cells that catalyze all types of biochemical reactions like digestion, respiration, muscular contraction and metabolism taking place in the living organisms. They are macromolecule that makes an unfavourable reaction able to occur. They accelerate the biochemical reactions and lead these reactions to completion which is not possible at ordinary temperature.

Prosthetic groups

These are cofactors tightly bound to an enzyme at all times.