HOMOLOGOUS SERIES:

 HOMOLOGOUS SERIES:

"A series of organic compound in which each member is different from the next member by a methylene (-CH2-) group is called homologous series".

All the members that differ from each other by methylene group, are called homologues. Each class of organic compounds has its own homologous series which can be represented by a general formula. For example, alkanes (saturated hydrocarbons) can be represented by a series of compounds. It can be represented by a general formula CnH2n+2 where 'n' shows the number of carbon atoms in the corresponding alkane.

As it is clear from alkane homologous series that each member is different from the adjacent member by CH3. Similarly, this series can be expanded beyond C10 to higher alkanes. Similar homologous series can be developed for alkenes, alkynes, alcohols, ethers, amines, carboxylic acids, carbonyl compounds etc.

CHARACTERISTICS OF HOMOLOGOUS SERIES:

*Each class of organic compounds has its own homologous series having same  general formula.

*All the members of homologous series have similar chemical properties.

* They have same general methods of preparation similar structural features.

*They have same functional group.

*The physical properties like melting point, boiling point, densities etc, increase down the series due to increase in their molecular masses.

For Example lets see homology in alcohol.

CH3CH2OH                               Ehtyl alcohol

CH3CH2CH2OH                        Propyl alcohol

CH3CH2CH2CH2OH                 Butyl alcohol 

CH3CH2CH2CH2CH2OH          Pentyl Alcohol

CH3CH2CH2CH2CH2CH2OH  Hexyl alcohol

Consider another example:

CH3CH2Cl                               Ehtyl Chloride

CH3CH2CH2Cl                  Propyl Chloride

CH3CH2CH2CH2Cl              Butyl Chloride

CH3CH2CH2CH2CH2Cl        Pentyl Chloride

CH3CH2CH2CH2CH2CH2Cl  Hexyl Chloride

NUCLEAR MAGNETIC RESONANCE (NMR) SPECTROSCOPY

NUCLEAR MAGNETIC RESONANCE (NMR) SPECTROSCOPY:

Nuclear magnetic resonance spectroscopy (NMR) is the most powerful tool available for organic structure determination. Like infrared spectroscopy, NMR can be used with a very small amount of sample, and it doesn't harm the sample. The NMR spectrum provides a great deal of information about the structure of the compound, and many structures can be determined using only the NMR spectrum. More commonly, however, NMR spectroscopy is used in conjunction with other forms of spectroscopy and chemical analysis to determine the structures of complicated organic molecules

MAGNETIC SHIELDING BY ELECTRONS:

Protons in a molecule are surrounded by electrons and exist in slightly different electronic (magnetic) environments from one another. The electron densities vary from one proton to another. Thus, the net field felt by a proton in a molecule will always be less than the applied field and the proton is said to be shielded. All of the protons of a molecule are shielded from the applied field by the electrons, but some are less shielded than others, because they may have less surrounding electron cloud and termed as deshielded protons. Deshielded protons are generally in vicinity of electronegative atoms in a molecule. More shielded protons absorb low radio-frequency radiations and their signals appear to the right side of spectrum, upfield region; while deshielded protons absorb high radio-frequency radiations and their signals therefore, appear at the left side of spectrum, downfield region.

PESTICIDES:

 PESTICIDES:

Pests harm crops and transmit diseases both to human and animals. Pesticides are the substances that can directly kill an unwanted organism or otherwise control by interfering with its reproduction process. The current ability to produce large amounts of food on relatively small amount of land had been made possible around the world by use of pesticides. At present more than ten thousand different types of synthetic organic pesticides have been formulated. They are broadly classified into several principal types according to their general chemical nature. The most important and widely used pesticides are insecticides (which kill insects), herbicides (which kill undesired plants) and fungicides (which control the growth of fungus on the plant).

The use of various pesticides also helped in the eradication of diseases such as malaria, yellow fever, bubionic plague and sleeping sickness.

Wide spread use of pesticides for getting greater crop yields if not properly checked and controlled has associated risks of contaminating the soil, plants and the water. The drainage water from the agricultural land mostly contains pesticides. Therefore if the use of any type of pesticide is not properly controlled it enters through various roots i.e., agricultural food products and drinking water into the food chain and thus pose serious health problems to both human beings and animals.

USES OF PVC and Nylon

 •USES OF PVC:

PVC or polyvinyl chloride, is a type of plastic used in numerous industries. It is durable, inexpensive and resistant to heat, water and chemicals.

*PVC plastic is manipulated to create a leather-like material called Rexine.

*PVC are used for pipes. These pipes are strong, light weight and less reactive.

*PVC plastic is used to form the insulating material on electrical wires.

*PVC is used to manufacture bottles.

* Other uses of PVC include medical tubing, PVC window frames, flexible packaging, blood bags, resilient flooring, vinyl paneling, drainage pipes, gramophones records, carpet backing, etc.

• USES OF NYLON:

Nylon is a versatile and incredibly useful material.

*Stockings_nylons strong fibres can be woven together to produce a lightweight silky fibre that is perfect for stockings.

*Parachutes-nylon is used in the manufacture of parachutes.

*Tents and camping equipment_ durability and resistance make nylon a great choice for all kinds of camping equipments.

*Boating and sailing_ nylon is used in the production of many sails and ropes.

*Nylon is used in moulded machine parts such as gears and bearings.

Lipstic and its composition

 LIPSTICK:

Lipstick are basically dispersions of colouring matter in a base containing a suitable blend of oils, fats and waxes suitably perfumed, flavoured and moulded in the form of stick and enclosed in a case. Some lipsticks are also lip balm, to add colour and hydration.

•CHEMICAL COMPOSITION OF LIPSTICKS:

The chemical composition of lipstick varies greatly. The general composition of lipsticks are;

*A mixture of non volatile oils,e.g. caster, vegetable, mineral or wool fat, lanolin oil.

*Mixture of waxes, e.g. bee wnax or carnauba.

* Colours

*Antioxidants

*Preservatives

Usually perfumes are also added in very small quantity to combat the unpleasant fatty odour of the oil. 

The oil makes the wax-based product soft and to be easily applied.

 In order to reduce the 'stickness', usually, esters of fatty acids (like 2-propyl myristate) is also added. 

Lipsticks are made from hydrophobic materials.

 The dyes are water_insoluble. 

Water soluble dyes such as green or blue food dyes can be used to provide lipstick colouration but they are, first combined with metal oxides such as aluminium hydroxide,Al(OH)3, to form an insoluble precipitate 

It is then suspended in the oil base of the lipstick.

 

Colour is a key ingredient of lipsticks.

 Silicones and oily material are also added to reflect light and provide shine.

Measurement of viscosity:

General principle:

     The measurement of viscosity of liquid is based on pioseulle's equation.

               n=πPtr^4/8VI

Where:

   V= volume of liquid

    r= radius of capillary tube

    l= length of tube

   P= pressure applied

Measurement of absolute viscosity:

 It is difficult to measure  directly the exact value of absolute viscosity because measurement of p,r and v is difficult.

So the viscosities of liquids are expressed in relative term

relative viscosity:

          "This is the ratio of viscosity of liquid to the viscosity of water taken as reference standard and this is called relative viscosity.

OSTWALD's VISCOMETER (measurment of relative viscosity):

It is used to measure the relative viscosity.

• It is a U- shaped glass tube with two marks 'x'&'y'.

•It has two bulbs 'A' and 'B'.

•The bulb A is at higher level than B.

•A definite volume of liquid is put in bulb B and then sucked in bulb A.

•The time of flow of liquid is noted .Similarly the time of flow of reference liquid water is also noted.

•Density of liquid is determined by "Specific gravity bottle".

•Follow8ng equation is applied to calculate Viscosity.

       n°/n= d°/d × t°/t

Where:

n°= viscosity of liquid

 n= viscosity of relative liquid

d°= density of liquid determined by Specific gravity bottle

d=density of reference liquid

t°=time of flow of liquid

t= time of flow of reference liquid

Viscosity and fludity

Defination:

    "Liquid's resistance to flow".

                      OR

    " The frictional effect between different layers of a flowing fluid ".

Explanation:

It is the property which opposes the relative motion of adjacent layers of liquid. 

The substances that cannot flow easily have large coefficient of viscosity. (such as honey)whereas the substances that can flow easily have small coefficient of viscosity (Such as water).

Factors:

It depends upon: 

•The strength of Intermolecular force 

•Structure of the compound

•Shape of the molecule

The force which is required to maintain the steady flow of liquid in direction of the force is directly proportional to the viscosity gradient which is normal to the direction of flow. 

Defination:

   "It is the force per unit area , needed to maintain unit difference of velocity between two parallel layers of the liquid , unit distance apart." 

Unit of viscosity "poise":

"When  a force of one dyne per square cm is maintained, between two layers which are 1cm apart and the difference of velocity between the two layers is 1cm per second, then it is called poise. "

           1poise =10^-1 kg m^-1 s^-1

            1 centipoise =10^-2 poise

            1 millipoise =10^-3 poise

Effect of temperature on viscosity:

   The viscosity of a liquid falls with the increase in temperature.

It is estimated that for each one degree rise of temperature, there is 2% decrease of viscosity.

Fluidity:

       " Fluidity is the reciprocal of viscosity".

The units of fluidity are reciprocal of viscosity.(poise^-1).