• They are generally gases, volatile liquid or low boiling points solids depending on their intermolecular forces and size of the molecules
• They are generally insoluble in water except those that contain polar groups (-OH group,-COOH group,-SO₃ groups) because they are non-polar
• They are soluble in organic solvent e.g. ether, acetone, benzene
• On combustion in oxygen they produce co₂ and water vapor
•  Reactions involving organic compounds are generally slow
• Most organic compound undergo isomerism
• Organic compound are covalent and do not conduct electricity because they do not ionized
• Organic compounds generally contain other groups of elements e.g. oxygen, nitrogen, surphur, metal

 The number of organic compounds that exist is greater than the sum total of all the compound of all the other elements put together. This is because carbon has a unique nature

 

Unique nature of carbon

1. Catenation:

It is the ability of an element to form strong covalent bond to his cells forming rings and chains

1. Multiple bond formation:

Carbon can form single, double and triple bond. This is because carbon can undergo hybridization to form sp3, sp2 and sp hybrid orbital. The EC of carbon during the s, p, d, f notation is 1s², 2s², 2p² .

• Carbon can neither gains nor lose 4 electrons to become C^-4 or C^-3 respectively. It uses its 4 electrons to form 4 covalent bonds.
• Carbon has a giant covalent or atomic structure.

Classification of organic compounds

The classification of organic compound is base on their carbon skeleton:

1. Aliphatic compound

These groups are made up of carbon compound with open chains of carbon atoms which could be branch or not. They could also be saturated or not.

            

 

1. Alicyclic

1. Heterocyclic                      

Here one or more other elements are contain in the rings of carbon atoms which can be satured or unsatured.

Fig:

1. Polycyclic

Here two or more carbon atoms are link together to form two or more cycle. The rings or cycles are heterocyclic.

Fig:

1. Aromatic

These are compound which contain benzene rings e.g. benzene, phenol, methyl/benzene, benzene acid.

Fig:

Bonding and shapes of organic compounds

In molecular theory, a covalent bond is the overlapping of atomic orbital with each containing an electron. At the excited state, the electronic configuration of carbon is 1s², 2s², 2p¹_x, 2p¹y_y, 2p¹_z.

Fig:

Carbon therefore has 4 atomic orbitals of equal energy which can overlap to form covalent bonds. Covalent bond is form by hybridization.

Hybridization: is the mixing or blending of atomic orbital of equal energy called hybrid orbital.

Formation of sigma bonds

Sigma bonds are formed by the following ways:

• When two s-orbital overlap to form a plum shape molecular orbital
• 

 

• When an s and p orbital overlap

Fig:

• A head-on overlap of two p orbital

Fig:

• During the overlapping of hybrid

Formation of pi (∏) bonds

Pi bonds are founded by the following ways:

• Side way or lateral overlap of two p orbital

Fig:

• During the overlapping of unhybridise orbiteils

 

SP³ HYBRIDIZATION

It is formed when one 2s orbitals combine with three 2p orbitals to form sp³ hybrid orbital during bonding will be directed towards the four corners of a tetrahedron to give a compound with a tetrahedral shape. Carbon to carbon single bond is form when two sp³ hybrid orbital overlap with the s orbital of hydrogen. These give a compound with the bond angle 109.5c

SP² HYBRIDIZATION       

It is formed when one 2sp combine with only one 2p orbital to form sp² hybrid orbital. It insult to the formation of carbon to carbon double bond like in alkenes with bond angle 20 degree and a planar shape.

This is formed when one orbital combine only one 2p orbitals to give sp hybrid orbital. It results to the formation of carbon to carbon triple bond, with a linear shape and bond angle 180 degree.

Fig:

De-localized bonds in Aromatic compounds

The bond length of carbon to carbon in benzene is 0.139nm. this is different from the carbon to carbon single bond length of 0.154nm and carbon double bond length of 0.133nm from x-rays studies. This implies benzene does not contain carbon to carbon single bond and carbon to carbon double bonds as purpose by the structure of Frederick kekule.

Fig:

Modern approach shows sp² hybridization to form three sp² hybrids orbital. The unhybridized two pz overlap laterally to form a ring of negative charges above and below to give a structure of benzene as bellow.

Fig:

 

ANALYSIS OF ORGANIC COMPOUNDS AND DETERMINATION OF STRUCTURE

 

This process involves;

• Preparation of organic compounds.
• Separation and purification.
• Qualitative analysis.
• Quantitative analysis.
• Determination of structural formula.

 

1. PREPARATION OF ORGANIC COMPOUNDS.

 

Considering the fact that that most organic reactions are very slow ( at room temperature ), the best method of preparing these compounds is by heating under reflux using reflux condenser. The reaction mixture could be dissolved in an organic solvent like methyl benzene. During refluxing, the mixture is heated and maintained as its boiling point temperature. The vapor produced condenses in the condenser and falls back and so, there is no lost of material. This method prevents;

• Lose of volatile components.
• Prevents accidents.
• It enables the reaction to get completion.

2. SEPARATION AND PURIFICATION.

Several methods are used depending on the solubility, boiling points, and impurities involved.

1. RECRYSTALLISATION

It is a method of separating solid impurities from a solid, which dissolves in a solvent. The impure sample is dissolved in a small amount of solvent e.g. Methanol. These hot concentrated solutions can be filtered off to remove the solid impurities.

Cooling could also crystallize the pure solid leaving the impurities in the solvent which could be removed by filtration using a BUCHNER FUNNEL at reduce pressure. Benzoic acid is purified by this method.

 

2. SUBLIMATION

This method is used to separate compounds that sub-lime (e.g. naphthalene, quinine etc.) from those that do not sub-lime the mixture is heated and the vapor produce allow to come to contact with a cold surface. Very few substances sub-lime, so these method is least used.

3. SIMPLE DISTILLATION

This method is used to separate volatile liquids from either a solid or a non-volatile liquid. It is mostly used for liquids with boiling points less than 140 degree celcius at atmospheric pressure. During boiling, the vapor from the volatile liquid condenses in the condenser while the impurities remain in the flask.

4. FRACTIONAL DISTILATION AND SOLVENT EXTRACTION

It is used to separate or purify an organic compound from solvent extraction and aqueous solution or suspension. Since organic compounds are soluble in an organic solvent, then water, we place the aqueous mixture in the separating funnel and then add an organic solvent e.g. beater. Two layers of mixtures (an organic layer containing the organic compounds and an aqueous layer containing the impurities.) , which can be separated using the separating funnel. The aqueous layer is removed through the tap while the organic layer is distilled to recover the pure organic compound and amines are purified by this method.

5. CHROMATOGRAPHY

It separates mixtures base on the affinity for the fixed phase (absorbant or stationary phase) and mobile phase (eluant). There are many types of chromatography:

•  Column Chromatography

The absorbant (gel, cellulose) etc is filled in a glass tube wetted with the solvent; when then put the mixture at the top of the column follow by the eluant. The different components will be absorbed at different level as the components runs under gravity and they leave the column at different time.

• Paper Chromatography

The paper is the fixed phase while the mobile phase is an organic solvent. The mixture to be separated is out on the paper and then dipped into the solvent. Where it is separated based on their difference in affinity for the fixed and mobile phase.

• Thin layer Chromatography
• Steam Distillation

Non-volatile impurities like inorganic solvent are separated from high boiling point liquids by steam distillation. One of the components we are separated should be insoluble, have a high R.M.M. and have vapor pressure of about hundred atmosphere.

Substances that decompose at or close to their boiling points are separated by this method. Their vapor pressure is higher than that of both component and the temperature at which the mixture boils is lower than that of either component. Steam is passed through the mixture to enable one of the components to distill at a lower temperature. The distillate will consist of water and pure liquids which can be separated by solvent extraction.

CRITERIA FOR PURITY

1. For solid

Pure solids have definite melting points or can melt over a temperature of 1 degree while impure solid can melt over a temperature of 5 degree. A pure solid will produce a single spot on a paper chromatography

2. For liquid

Pure liquid have sharp and constant boiling point at a particular pressure leaving behind no residue. Azeotropic mixture also have sharp boiling point at a particular pressure but other liquid will have sharp boiling points at two different pressures.

C- QUALITATIVE ANALYSES

It involves the use of chemical test to identify the constituent of a compound which most contain carbon and hydrogen, nitrogen, sulphur, a metal, etc could also be present.

1. Test for carbon and hydrogen

A small sample of organic compound is crushed with copper II oxide and healed in a hard glass tube. Hydrogen is converted into water, water will turn while anhydrous copper II sulphate to blue.

H₂O + CUSO₄                                          CUSO₄.5H₂O

2[H] + CUO                          H₂O + CU

The formation of co₂ will indicate the presence of carbon co₂will turn lime water milky.

                        [C] + 2CUO                          CO₂ +2CU

                        CO₂ + CA (OH)₂                               CACO₃ + H₂O

Lassaigne’s test for N₂, S, etc (sodium fusion test) the organic compound is heat with sodium pellets in a hard glass tube and then immersed in cold water for it to break . the resulting mixture is boiled for a few minutes and filtered, the filtered will contain sodium cyanide (NAC-N), sodium sulphite, sodium chloride, sodium iodide in case the original compound contain nitrogen (N), sulphur (s), respectively. Is then divided into portions and use for the following tests

2. Test for nitrogen

A simple of the alkaline filtrate boiled with iron II sulphate solution. The filtrate is alkaline because it contain sodium hydroxide from the reaction between sodium and water.

                        Fe _(aq) + OH _(aq)                     Fe (oh)_2(aq)

The result solution is ioded and 2 to 3 drops of iron III chloride followed by HCL are added. A Prussian blue or deep blue of iron III hexacyano ferrate (II) is formed.

                        Fe(OH)_2(s) + 6CN_aq                  [Fe(CN)₆]_aq + 2OH^-

                       3[Fe(CN)₆]_aq^4- + 4 Fe^3t _(aq)              Fe₄[Fe(CN)₆]_3(s)

3. Test for sulphur (sulphide test)

A simple of the filtrate is acidified with dilute ethanoic acid followed by about 1cm³ of lead acetate solution (CH₃COOPL). A black of lead II sulphide (pb so₄) indicates the presence of sulphur. Or a purple solution will indicate the presence of sulphur when the filtrate is heat with sodium nitropruside.

4. Test for halogen

Hydrogen cyanide and hydrogen sulphide are removed using hot access nitric acid. The mixture is then heated with silver nitrate and then aqueous ammonia added.

• Chloride: a white of silver chloride soluble in aqueous ammonia will indicate the presence of chloride.

Ag⁺_(aq) + CL^-_(aq)                                 Agel_(s)

• A pal yellow of silver bromide slightly soluble in aqueous ammonia will indicate the presence of bromide.

Ag⁺_(aq) + Br^-_(aq)                                 AgBr_(s)

• A yellow of silver iodide insoluble in aqueous ammonia indicates the presence of iodide.

Ag⁺_(aq) + I^-_(aq)                        AgI_(s)

5. Test for phosphorus

The general method to test for inorganic compounds containing a metal is by the use of aqueous sodium hydroxide or the use of a flame. The flame test compound is initied against the Bunsen flame and each metal ion has it flame color.

Metal  ion	Flame color
Sodium ion Potassium (k) Copper II (Cu2+) Calcium (Ca2) Barium (Ba2+) Structium (Sr2+)	Golden yellow Lilac Blush green Brick red Apple green or pale green Bright red

 

6. Test for functional groups

• OH group: dense white flumes of hydrogen gas are produce with reacted with Pcl₅ or hydrogen is evolve when reacted with a metal
• Carboxylic group (COOH): sodium hydrogen carbonate will produce co₂ (colorless gas which turn lime water milky) when reacted with carboxylic acids
• Primary, secondary and tertiary aminas: they are distinctguish using nitrous acid
• Aldehydes and ketones will produce orange with 24-DNPH (2.4 dinitro phehyl hydrazine).

            D- QUANTITATIVE ANALYSIS

It deals with what amount of each element present in the compound:

1. Carbon and hydrogen

A specify mass or given mass of the compound is healed in a stream of oxygen or in copper II oxide. Hydrogen is oxidize to water while carbon is oxidize to carbon dioxide. They are absorb using anhydrous calcium chloride and their masses obtains respectively.

                        [C.H] + O₂                 CO₂ + H₂O

For carbon                                                                          for hydrogen

C                     CO₂                                                                             H                     H₂O

12                   44                                                                  2                     18

X                     MCO₂                                                            X                     MH₂O

X   = 12/44  *   MCO₂                                                                   X    = 2/18  * MH₂O

%C  =  12 * M                     *100%          

           44 * RMM of cpd

2. Nitrogen

The specified mass of the compound is healed in powdered Cuo in a stream of co₂. All the nitrogen present in the compound is connected to nitrogen or oxides of nitrogen which will be converted to nitrogen by passing it over copper. The volume of nitrogen collected in the nitrimeter is used to calculate it’s percentage composition. This is the Duma’s method

            % of N =2.8    *   volume of N₂  *100%  

                        22400 * mass of cpd        

3. Sulphur

A specify mass of the compound is heated with flumiry nitric acid in a sealed tube. All the sulphur will be converted to sulphuric acid which is to barium sulphate using barium chloride. The percentage of sulphur is calculated as:

            % of S = 32    *  mass   of   Ba So₄            *100%

                        RMM of BaSo₄ * mass of cpd

• Halogen

We heat a specific mass of compound is heated with fluming nitric acid and then silver nitrate. Any hydrogen present will be converted to Ag^x (x=halogen). If the halogen is a chlorine then                      %(  cl = 35.5    *    mass of Agcl        *100%

      RMM of Agcl * mass cpd)

• Oxygen

The percentage of oxygen is the remainder when the percentage of all the other elements are subtracted from 100

 

EMPERICAL AND MOLECULAR FOMULA

-Emperical l formula:  The EF of a compound expresses the simple mole ratio of the different in one mole of a compound.

-Molecular Formula: It gives the actual number of atoms of each element present in one molecule of a compound.

  Examples

2.40g of a compound containing carbon, hydrogen, and oxygen gave on combustion 3.52g of co2, 1.44g of water and the molar mass of the compound is 180. Determine the E.F and  M.F of the compound.