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NATIONAL LEVEL ONLINE TEST
Polymers and Biomolecules are very important chapters in JEE Main Chemistry. Generally, 1 question is asked from each chapter, Polymers and Biomolecules, which bears about 8 marks in total. Therefore, their overall weightage in JEE Main is 2-3%. These chapters cannot be skipped. Most of the questions asked from Polymers and Biomolecules are quite easy to score.
Some of the topics tested under Polymers include - Different Types of Polymers and Polymerization. Lipids, Carbohydrates, and Proteins are some of the topics tested under Biomolecules. Read the article below to find study notes for polymers and biomolecules to help you cover JEE Main Chemistry Syllabus.
These polymers are formed through the repeated addition of monomer molecules that contain double or triple bonds. Some examples include, polythene (from ethene) and polypropene (from propene).
These are addition polymers that are formed through the polymerisation of a single monomeric type.
|Polyvinyl chloride||Vinyl chloride|
These are addition polymers that are formed by more than one type of monomer.
|Nylon-6,6||Hexamethylenediamine and Adipic acid|
|Buna - S||Styrene and Butadiene|
|Buna - N||Acrylonitrile and Butadine|
Practice withJEE Main Question Paper
Random Copolymers: In these polymers, the monomer units consist of random distribution in the chain segment.
nA + nB → -A-A-B-A-B-B-A-B-A-A-A-B-
Alternating Copolymers: In these polymers, the monomer units occur in an alternative fashion in the polymer chain segment.
nA + nB → -A-B-A-B-A-B-A-B-
Block Copolymers: In these polymers, various blocks of identical monomer units are alternative with one another.
nA + nB → -A-A-B-B-B-B-B-A-A-A-A-A-B-B-B-B-B-A-
Graft Copolymers: In these polymers, the homopolymer branches of one polymer unit get grafted onto the homopolymer chain of another monomer unit.
Any molecule that exists in living organisms is known as a biomolecule. Biomolecules include macromolecules like lipids, carbohydrates, nucleic acids, and proteins, and small molecules like primary and secondary metabolites, and natural products.
Proteins are biomolecules which are crucial for the existence of living organisms. Amino acids are known to be the building blocks of proteins. Naturally occurring amino acids are 22 in number. They consist of the carboxyl group, amino group, hydrogen atom, and R group, which is the alkyl group. The R group is variable. This means that it varies with different amino acids. The 4 groups mentioned are attached to a single carbon atom that is called the Alpha-Carbon.
Fig.1. Structure of Amino Acid
The simplest form of amino acid is glycine. In glycine, the R group undergoes replacement with the hydrogen atom. The bond formed among the two amino acids is known as the peptide bond.
Fig.2. Amino Acid Sequence-Protein
Primary Structure: This is the sequence of amino acids in a protein. The left end is shown by the first amino acid and the right end is shown by the last amino acid. The first amino acid is known as the N-terminal amino acid. The last amino acid is known as the C-terminal amino acid.
Secondary Structure: The protein is not a linear chain of amino acids. Instead, the chain bends at some points and also forms helices. By repeating the local structures regularly, the secondary structure to protein gets formed.
Tertiary Structure: This is the general shape of a protein molecule and also the spatial relationship between the secondary structures. In simpler words, the different folds that provide three-dimensional looks to a protein make up its tertiary structure.
Quaternary Structure: This is the way in which the individually folded polypeptides are arranged with regard to one another.
Fig.3. Structure of Protein
Lipids are generally insoluble in water. They are known to be fatty acid esters. Importantly, lipids are the primary element of cell membranes. They can either be simple fatty acids or contain phosphorus and phosphorylated organic compounds. Those which contain phosphorus are known as phospholipids.
Fig.4. Structure of Phospholipids
A fatty acid consists of a carboxyl group which is attached to an R group. The R group could be a methyl, ethyl or a higher number of the CH2 group (1 carbon to 19 carbons).
Primarily, there are two kinds of fatty acids - saturated and unsaturated fatty acids.
Saturated fatty acids do not have any double bond among the carbon atoms. An example is butyric acid.
Unsaturated fatty acids have double bonds among the carbon atoms. An example is linoleic acid.
Carbohydrates consist of atoms of carbon, hydrogen, and oxygen. They include sugars, starch, and cellulose. The simplest form of carbohydrates is glucose. The bond among two sugar molecules is called the glycosidic bond.
Fig.5. Structure of Glucose
Carbohydrates which are made up of a single sugar molecule are called monosaccharide. An example is glucose. Monosaccharides that consist of more than one unit of sugar molecule are called oligosaccharides. An example is fructose. Lengthy chains of sugars are known as polysaccharides. When a polysaccharide consists of similar monosaccharides, it is known as a homopolymer. An example is cellulose. When a polysaccharide consists of different monosaccharides, it is known as a heteropolymer.
The right end of a polysaccharide chain is known as the reducing end and the left end is known as the non-Reducing end.
Fig.6. Reducing and Non-Reducing ends in Maltose
Note that starch is a homopolymer of glucose. It is the primary storage sugar in plants. In a similar manner, the storage form of sugar is glycogen in animals. This is stored in their livers. When the body requires glucose during starvation or fasting, glycogen breaks down into glucose in order to fulfil the energy needs of the body. The sugar existing in DNA is deoxyribose and in RNA, the sugar is ribose.
Nucleic Acids are organic molecules that exist in living cells. They are polymers of nucleotides. The three chemically significant components of a nucleotide are - phosphate group, sugar called deoxyribose, and nitrogenous bases. Nitrogenous bases are of two types - purines and pyrimidines. Purines include adenine and guanine. Pyrimidines include thymine and cytosine. DNA contains all the four bases - adenine, thymine, guanine, and cytosine. However, in RNA, thymine gets replaced by uracil.
DNA is a nucleic acid biomolecule.
Fig.6. Structure of Nitrogenous Bases
Formation of Polymers
a) In chain reaction polymerization
Rad. + CH2 = CH2 → RadCH2CH2→ RadCH2CH2CH2CH2× → etc.
b) In step reaction polymerization
c) Free-radical vinyl polymerization
a) Natural Rubber
This is an addition polymer of isoprene (2-methyl-1,3-butadiene). On an average, it has a chain length of 5000 monomer units of isoprene.
b) Synthetic rubber ((Polychloroprene) or Neoprene)
It is formed through the free radical polymerisation of chloroprene in
A thermoplastic and need not to be vulcanised. Synthetic rubber is superior to natural rubber because of its resistance to the reactions of air, light chemicals, heat, alkalis, and acids that are lower than 50% in strength.
c) Buna rubbers
i) Buna - N or GRA: A synthetic rubber that is formed through copolymerisation of one part of aryl nitrile and two parts of butadiene.
It is more rigid and has low response to heat. It is very resistant to the swelling action of petrol, oils, and other organic solvents.
ii) Buna -S or GRS (General Purpose Styrene Rubber): This is a copolymer made from three moles of butadiene and one mole of styrene. It is an elastomer.
It is typically vulcanised with sulphur and compounded with carbon black. It is very resistant to wear and tear.
d) Teflon: It is a polymer of tetrafluoroethylene (F2C=CF2) which when polymerized produces Telfon.
It is a thermoplastic polymer that has a high softening point (600K). It is inert to most chemicals with the exception of fluorine and molten alkali metals. Also, it withstands high temperatures.
e) Nylon - 66: This is a condensation polymer that is formed from a reaction between adipic acid and hexamethylenediamine. It is a thermoplastic polymer.
f) Nylon 6 or Perelon: This is a polyamide that is made from the heating of caprolactum at 530-540 K for a long period of time.
h) Phenol-formaldehyde polymer
An example is bakelite novolac.
Points to Remember for Biomolecules
Classification of carbohydrates
Monosaccharides and oligosaccharides are crystalline solids. They are soluble in water and are sweet in taste. Collectively, they are called sugars. Polysaccharides are amorphous, insoluble in water, and have no taste. They are known as non-sugars.
The change with time in the rotation of an optically active sugar in solution to an equilibrium value. During this process, the ring opens and later recloses in the inverted position or in the initial position producing a mix of a-and-b-forms.
Reactions of Glucose
a) With HI/P: It goes through reduction to produce n-hexane and with sodium amalgam, it produces sorbitol.
e) Oxidation: The glucose when oxidized with Br2 produces gluconic acid which on further oxidation with HNO3 forms glucaric acid.
f) With Tollen reagent and Fehling solution: Glucose gives silver mirror and red ppt. of Cu2O respectively.
g) With acetic anhydride: In the presence of pyridine, glucose gives pentaacetate.
j) Glycoside formation: When a small quantity of gaseous HCl gets passed into a solution of D (+) glucose in methanol, the reaction results in the production of amomeric methyl acetals.
Carbohydrate acetals are generally known as glycosides and an acetal of glucose is known as glucoside.
k) Kiliani - Fischer Synthesis: A process of lengthening the carbon chain of an aldose.
l) Ruff Degradation: A contrast to Kiliani Fischer synthesis which can shorten the chain by a similar unit.
a) Sucrose: A non-reducing sugar that is made through the condensation of one molecule of glucose and one molecule of fructose.
Hydrolysis: The hydrolysis of sucrose with hot dilute acid produces D-glucose and D-fructose.
i. It is a polymer of glucose.
ii. It is a mixture of two components, a water soluble component known as amylose (20%) and a water insoluble component known as amylopectin (80%).
iii. Amylose and amylopectin are the polymers of a-D-glucose.
iv. Amylose is a linear polymer of a-D-glucose.
vi Amylopectin is a highly branched polymer
Amino acids are molecules that consist of two functional groups, a carboxylic group and an amino group.
H2N CH2 COOH : Amino acetic acid, or Glycine
CH3 CH (NH2) COOH : a - Amino propionic acid or Alanine
H2N CH2 CH2COOH : b - Amino propionic acid
Acidic Amino Acid: Have a second carboxyl group or a potential carboxyl group in the form of carboxamide.
Basic Amino Acids: Have a second basic group that could be an amino group.
It is the hydrogen ion concentration of the solution in which a specific amino acid does not migrate due to the influence of an electric field.
Peptides are the amides that are produced through an interaction among amino groups and carboxyl groups of amino acids.
They are called dipeptides, tripeptides, or polypeptides depending on the number of amino acid residues per molecule.
Two amino acids are connected through a –CO-NH group. This is known as the peptide bond.
Q1: What is the correct functional group X and the reagent/reaction conditions Y in the scheme given below?
(A) X = COOCH3, Y = H2/Ni/heat
(B) X = CONH2, Y = H2/Ni/heat
(C) X = CONH2, Y = Br2/NaOH
(D) X = CN, Y = H2/Ni/heat
Condensation polymers are produced through the condensation of diamine or diols with dicarboxylic acids.
Therefore, X may be -COR, -CONH2, -CN
a) What is the structure of nylon-6 which is made through alkaline polymerisation of caprolactam?
b) Suggest a mechanism for this process. Is the polymerisation of the chain-reaction or step-reaction type?
The reaction is an anionic chain-reaction polymerization. It involves nucleophilic substitution in the acyl group of the cyclic amide. The base can be OH–or the anion made through abstraction of the –NH proton from one molecule of lactam.
Q3: Identify the compound C.
a) Give structures for H through K. Given,
b) Explain the last step.
(c) What is net structural change?
(d) Name this overall method.
(e) What is the possibility of epimer formation?
a) H is an oxime HOCH2(CHOH)4CH = NOH; I is the fully acetylated oxime, AcOCH2(CHOAc)4CH = NOAc which loses 1 mole of HOAc to give J, AcOCH2(CHOAc)4 CºN; K is an aldopentose, HOCH2(CHOH)3CHO.
b) The acetates go through transesterification to produce methyl acetate. This frees up all the sugar OH’s. After this, the reversal of HCN addition happens.
c) From the carbon chain, there is a loss of one C.
d) Wohl degradation.
e) The a-CHOH turns into –CH = O with no configurational changes of the other chiral carbons. Therefore, no epimers get formed.
a) How can aldohexose be used to synthesize 2-ketohexose?
(b) As glucose gets converted to fructose through this process, what can be said about the configurations of C3, C4 , and C5 in the sugars?
Aldohexose reacts with one molecule of phenylhydrazine that condenses with the aldehyde group to produce phenylhydrazone. When warmed with a big quantity of phenylhydrazine, the secondary alcoholic group which is adjacent to the aldehyde group gets oxidised to a ketonic group by another molecule of phenylhydrazine. The third molecule of phenylhydrazine condenses to produce osazone with this ketonic group. The phenylhydrazine group gets shifted from osazone to C6H5CHO and gives C6H5CH = N×NHC6H5 and a dicarbonyl compound known as an osone. The more reactive aldehyde group of the osone gets reduced and produces the 2-ketohexose.
b) The configurations of the carbons that do not change in the reactions should be identical to be able to get the same osazone.
Q3: Why should the isoelectric point for Aspartic acid (2.98) be much lower than that of leucine?
Solution: This could be explained by considering the ion equilibria given below -
It is evident that the ions (A) and (B) are neutral, while (C) is a cation and (D) is dianion. In the species (D), the anion is found from the second —COOH group that exists in aspartic acid and is not possible in leucine. At neutral pH, a sizeable concentration of (D) will exist in the aqueous solution. It will hence be necessary to reduce the pH of such a solution when the formation of (D) has to be suppressed to a stage where the anions and cations exist in equal concentration (the isoelectric point).
As these are mostly theory-based, it is highly recommended that you draw all the diagrams and equations of every concept multiple times.
Attempt questions from within a particular text and those after the chapters.
Focus primarily on preparing from NCERT books because most of the questions asked in JEE Main Chemistry are from them.
While attempting MCQs, take a moment to mentally visualize the concepts, diagrams, and equations you have learnt that pertain to a specific question. Then, choose the correct answer.
|Polymer||Large molecules that have a high molecular mass and are formed by a combination of small units known as monomers.|
|Polymerization||The process of polymer formation from monomers.|
|Natural polymers||Derived from plants and animals. Examples: proteins, starch, cellulose|
|Synthetic polymers:||Synthesised in the laboratory from natural products. Example: buna s and nylon 6, 6|
|Addition Polymers||Formed through the repeated addition of monomers that have multiple bonds.|
|Homopolymers||Addition polymers that are formed from a single monomeric type.|
|Copolymers||Addition polymers that are formed from two different monomeric types.|
|Condensation polymers||Formed through the repeated condensation of distinct bi or tri-functional monomer units.|
|Fibres||Long, thin, and threadlike material which is characterized by high tensile strength. Natural fibres include cotton, wool, and silk.|
|Elastomers||Have a high degree of elasticity characteristic of rubber Examples - buna N and buna S When the stretching force is taken away, the molecular chains do not stay extended and aligned but revert to their original conformations.|
|Thermoplastic polymers||Soften when heated and stiffen when cooled Example: polythene, polystyrene, and PVC|
|Thermosetting polymers||No softening when heated and thus, cannot be remoulded. Example: bakelite|
|July 5 to 15, 2020||Physical Chemistry carries the highest weightage in JEE Main Chemistry. Important chapters from this topic like Atomic Structure, Electrochemistry, and Equilibrium can be studied first. Then, study chapters with lower weightage such as Surface Chemistry and Solid State. Select two chapters every day and understand all the important concepts.|
|July 16 to 26, 2020||This week can be used to study Organic Chemistry. Dedicate more time to important chapters like Aromatic Compounds, Alkyl Halides, Alcohol, and Ether. Then, study less significant chapters like Biomolecules and Carbonyl Compounds.|
|July 27 to August 8, 2020||You can study Inorganic Chemistry. Begin with the most important chapters such as Chemical Bonding, p Block, and s Block. Then, study chapters like Metallurgy and Qualitative Analysis that have a lower weightage.|
|August 9 to 20, 2020||Go through all formulas and basic concepts. Attempt a number of previous year’s papers for better practice. Take questions from the Chemistry section and answer them as fast as possible (45 minutes - 1 hour).|
|August 21 to 31, 2020||Give mock tests everyday. Revise important points from all chapters.|
|September 1 to 6, 2020||Go through the analysis of the ongoing JEE Main papers.|