Category: Chemistry Notes PPT

Combustion is the process of burning some substances at high temperatures. It is an exothermic reaction that happens between fuel and oxygen, producing a gaseous substance (smoke) as a product. Combustion is of two types, one is complete combustion and another is incomplete combustion. Hydrocarbons are compounds made only with the elements of hydrogen and carbon. Hydrocarbons are broadly classified as alkanes, alkenes, and alkynes.

Complete Combustion of Alkanes

It is the process of burning the alkane in the presence of sufficient air or oxygen; it produces carbon dioxide, water, and a huge amount of heat as a product. For example: 

1. With Propane ( C3H8 ), the complete reaction is given as follows:

             C₃H₈ + O₂ → 3CO₂  + 4H₂ 

2. With Butane (C₄H₁₀), the complete combustion reaction is given as follows: 

            C₄H₁₀ + O₂ → 4CO₂  + 5H₂ 

The generalised form of this reaction is as follows:

C_nH_2n+2 + ((3n + 1)/2) O₂ → nCO₂  + (n+1)H₂O

In general, it is used as a fuel since it produces a huge amount of heat.

Incomplete Combustion of Alkanes

It is the process of burning alkane in the absence of sufficient air or oxygen. It produces carbon and carbon monoxide as a product whereas carbon monoxide is a by-product that is a colorless poisonous gas. For example:

With methane (CH₄), the incomplete reaction is given as follows:

CH₄ + O₂ → C  + 2H₂O

The carbon black which is formed as a product of the combustion process is used in the manufacturing of inks. 

Combustion of Hydrocarbons (Alkene)

Complete Combustion of Alkene

Like the same as an alkane, alkene also undergoes complete combustion. It occurs in the presence of excess air or oxygen for combustion. For example:

   C₂H₄ + 3O₂ → 2CO₂  + 2H₂O

Incomplete Combustion of Alkene

It happens in the absence of oxygen during the combustion process and carbon monoxide is formed as a product instead of carbon dioxide. For example:

 C₂H₄ + 2O₂ → 2CO  + 2H₂O

Combustion of Hydrocarbons  

It is the process of burning the hydrocarbons which leads to breaking the bonds either in the presence or in the absence of excess oxygen.

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Complete Combustion of Hydrocarbons

It is the process of burning hydrocarbons in excess of oxygen and yields carbon dioxide and water as a product. Oxygen should be present in excess and hydrocarbon is used as a limiting reagent to achieve this process. 

Incomplete Combustion of Hydrocarbons

It is a process of burning hydrocarbons in the absence of excess oxygen and produces the most oxidized form of carbon which is carbon dioxide as a product. We should have oxygen as a limiting reagent and hydrocarbons as an excess reagent.

The “sooty” flame is produced by the incomplete combustion of a hydrocarbon, due to the presence of carbon ( C ). 

Hydrocarbon Formula of Complete Combustion

The general form of this combustion reaction is as follows:

Methane  +  oxygen gas  →  carbon dioxide gas + water vapour

Hydrocarbon Formula of Incomplete Combustion

The general form of this incomplete reaction is given as follows:

methane  +  oxygen gas  →  solid carbon  +  water vapour

Types of Combustion

Different types of combustion are as follows:

Rapid combustion: Rapid combustion is a type of combustion when quick heat energy is needed for the reaction to take place. A large amount of heat and light energy is produced in this type of reaction. The combustion occurs as long as the fuel is available. For example, when we light a candle, it will burn until the wax burns out. 

Spontaneous combustion: This type of combustion occurs spontaneously. This means that this type of reaction does not need any external energy for the combustion to begin. It occurs due to self-heating. This type of combustion takes place in substances with low-ignition temperatures. The process starts as soon as the temperature rises above the ignition point. The combustion will take place in the presence of oxygen. 

Explosive combustion: This is a type of combustion in which the reaction occurs very rapidly. This combustion occurs when something is ignited to produce heat, light, and sound energy as in firecrackers. 

Solved Examples

1. Ethanol is a fuel source in an alcohol lamp. The formula for ethanol is given by C₂H₅OH. Write the balanced equation for the process of combustion of ethanol.

Solution:

Step 1: Think of the given problem. The question is given on ethanol which is a reactant and also with oxygen. Carbon dioxide and water are the products.

Step 2: Write the skeleton equation and solve:

C₂H₅OH (l) + O₂ (g) →  CO₂ (g) + H₂O (g)

Now balance the equation.

C₂H₅OH (l) + 3O₂ (g) →  2CO₂ (g) + 3H₂O (g)

Evaluate the number of each element present on the reactant and product side.

Interesting Facts:

Nearly 21% of the air in the atmosphere is filled with oxygen. To get complete combustion, it is necessary to have plenty of air, mainly oxygen in it. Natural gas and petrol are such fuels that have hydrocarbons.

A hydrocarbon is a compound made of only 2 elements namely carbon and hydrogen atoms.

The interesting thing is, that it is found in crude oil and can be separated by fractional distillation. The bond between them is non-polar covalent bonds.

Summary

Combustion includes the burning of organic substances and it is a chemical reaction. 

Combustion includes burning of the organic compound and releasing carbon dioxide and water and releasing a lot of heat energy.

Combustion is an important process and hydrocarbons are the main source of energy for domestic and industrial processes. 

Combustion of fossil fuels such as natural gas is an example of such a chemical reaction. 

The field of Stereochemistry involves the study of bond distances and dihedral angles along with the basic principles, conformations, and configurations. It includes the methods of writing structures in two-dimensional and three-dimensional projections. It involves the atom group configurations in a molecule and the energy associated with these configurations. Atom groups usually rotate around different carbon-carbon axes, and the various shapes obtained are called conformations. The compounds that have the same molecular formula are known as isomers. When a group of atoms that make up the molecules of different isomers is bonded together then a constitutional isomer is formed.

Conformational Isomers

It involves rotation about sigma bonds and does not have any difference in the connectivity or geometry of the bonding. Two of the same molecules that only differ in terms of the angle of about one or more sigma bonds can be categorized as conformational isomers or conformers. If the group is large enough to significantly affect the rotation energy, it tends to prefer certain spatial arrangements. The spatial structures of the groups give rise to conformers.

Types of Conformational Isomers

1. Eclipse Conformation

The carbons are aligned in a way such that the hydrogen atoms are lined up with one another. It creates a steric hindrance between them. The hydrogen atoms attached to the two carbon atoms are as close to each other as possible in the eclipsed conformation. It is termed to be a little unstable due to the closeness of hydrogen atoms.

2. Staggered Conformation

Here the hydrogen atoms attached to the two carbon atoms are as far away from each other as possible. In the staggered conformation, the atoms are all equally spaced from each other, and these conformations are more stable than the eclipsed conformation and are more favoured. The reason for it being more stable is that the hydrogen atoms are far away from each other. The spacing creates minimum repulsive force and minimum energy between the electron clouds of C-H bonds.

Conformational Isomers of Ethane

Ethane, organic compound, is a colourless and odourless gas at room temperature. It consists of seven sigma bonds and six carbon-hydrogen bonds. The six carbon-hydrogen bonds protrude two carbons at 120° angles. Its lowest energy conformation is called the ‘staggered’ conformation. In this conformation, all of the C-H bonds on the front carbon are positioned at 60° relative to the back carbon’s C-H bonds. Along with the 60° positioning, the distance between bonds is also maximized. 

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Furthermore, upon 60° clockwise rotation of the front CH3 group, the molecules now attained the highest energy conformation of ethane, which is the ‘eclipsed’ conformation. In this conformation, the hydrogens on the front carbon are as close as possible to the back carbon’s hydrogens. The energy produced by the eclipsed conformation is 3 kcal/mol higher compared to the staggered conformation.

Conformational Isomers of Butane

The alkane called Butane has C-C bonds. It is a little different than that of ethane. In butane, when the molecule is rotated at the C-C bond axis, different conformational isomerism is obtained. Butane has two substituents, which is the methyl group attached to the two end carbon atoms. The methyl group is more extensive than hydrogen atoms. If the front methyl group is rotated by 60°, then we attain the gauche or staggered conformation of butane. If we rotate the methyl group by 120°, then the gauche turns into what is known as the eclipsed conformation of butane.

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When two fragments are joined together with the help of a metal catalyst to form a variety of reactions, then such types of reactions are known as coupling reactions in the field of organic chemistry. Metal catalysts are used because they increase the rate of the reaction without disturbing the thermodynamics of the reaction as transition metals are good catalysts. Organic chemistry is the division of chemistry that contains compounds formed from carbon in the field of organic chemistry. Here, we will be discussing the concept of coupling reactions and also their various types and applications in organic chemistry.

Principle of Coupling Reaction

When two similar or dissimilar types of chemical species react together with a common intermediate with the help of a metal catalyst to get a new product, then this type of reaction is called a coupling reaction.  Coupling reactions are of two types based on their chemical species which can either be of the same or different types. Coupled reactions are those reactions that contain a common intermediate and where energy is being transferred from one side to another side of the reaction. These reactions are done in the presence of metal catalysts. Metal catalysts are used because metals are a good catalyst as they take away electrons from other molecules. Catalyst is used in chemical reactions because when we add a catalyst in a chemical reaction, then without affecting the thermodynamics of the reaction, it eventually increases the rate of the reaction.

For Example: 

• Endogenic formation of ATP which is coupled for the dissipation of protein gradient.

• ATP + Glucose [rightarrow] ADP + glucose – 1- Phosphate

• Glucose – 1 – phosphate + fructose [rightarrow] sucrose + phosphate

• Sucrose is obtained from glucose and fructose with the expansion of energy stored in the form of ATP.

Coupling Reaction Examples

When organic halide reacts with an organometallic compound with general formula R-M, it facilitates the formation of a new carbon–carbon bond.

Also if organic halide has general formula R-M, then the new compound formed will be R-R’. ( where R= organic fragment and M= main group).

Here is an example of a coupling reaction below where R1 and R3 are alkanes, alkene, or an alkyl group and R2 is the hydrogen group.

Benzenediazonium Chloride + Phenol (Para Position) [rightarrow] p-hydroxyazobenzene

Types of the Coupling Reaction

There are two types of coupling reactions based on their chemical species.

1. Homo – Coupling Reaction: Homo means similar or the same. When two similar types of chemical species are combined to form a new compound, then they are known as homo-coupling reactions.

For example, the Wurtz reaction, Glaser coupling.

The general formula for Wurtz reaction is as follows:

2R – X + 2Na [rightarrow] R-R + 2(Na+X–)

2. Hetero – Coupling Reaction: Hetero means different or which are not similar. When two different types of chemical species are combined or they are reacted together to form a new product, then they are known as hetero-coupling reactions. Hetero-coupling reactions are also known as cross-coupling reactions.

For example, the Grignard reaction, Suzuki coupling.

Hetero coupling reactions are also known as cross-coupling reactions. These reactions are done in the presence of a metal catalyst to increase the rate of the reaction.

Azo Dyne Coupling Reaction: An organic compound with functional group  R−N=N−R′ where R and R’ are aryl groups. They belong to the family of azo compounds. They are insoluble in water and other solvents. They are used for the preparation of textile, leather objects, and some food products.

The reaction of Azo dyne is as follows:

Applications of the Coupling Reaction

There are various applications where coupling reactions are used. Some are listed below:

• Coupling reactions are used for various treatments such as for the formation of pharmaceuticals, polymers, and some other natural products.

• Coupling reactions are used for the formation of various conjugated polymers by using metal catalysts.

• For the production of various natural products, coupling reactions are used.

• Cross-coupling reactions are used for the preparation of monomers and polymers.

• Also, the reaction of Suzuki is used for the production of synthetic complex compounds. For example, the production of caparratriene which is highly effective in the treatment of leukemia.

Conclusion

In this article, we have learned about coupling reactions, their types, a few examples, and applications. We may carry on this learning process with more interesting topics of chemistry which will also help you in competitive exams like JEE and NEET.

Along with adenine, guanine, and thymine, cytosine is one of the four major bases present in DNA and RNA (uracil in RNA). It’s a pyrimidine derivative with two substituents and a heterocyclic aromatic ring (an amine group at position 4 and a keto group at position 2). Cytidine is the nucleoside of cytosine. It forms three hydrogen bonds with guanine in Watson-Crick base pairing.

Cytosine Structure

Cytosine is an aminopyrimidine with the amino group at position 4 and is pyrimidin-2-one. It acts as a human metabolite, a metabolite in Escherichia coli, a metabolite in Saccharomyces cerevisiae, and a metabolite in mice. It’s a pyrimidine nucleobase, pyrimidone, and aminopyrimidine all rolled into one. The molecule has a planar shape, and in the DNA double helix, cytosine forms three hydrogen bonds with Guanine. In RNA, which is made up of cytosine and ribose, the nucleoside of cytosine is cytidine. It’s called deoxycytidine in DNA, and it’s made up of cytosine and deoxyribose. The deoxycytidylate nucleotide of cytosine in DNA is made up of cytosine, ribose, and phosphate. A heterocyclic aromatic ring, an amine group at C-4, and a keto group at C-2 make up cytosine.

Cytosine Chemical Formula

C₄H₅N₃O is the molecular formula for cytosine. A heterocyclic aromatic ring, an amine group at C-4, and a keto group at C-2 make up cytosine. Cytosine forms the nucleoside cytidine when it binds to ribose, and deoxyribose forms deoxycytidine when it binds to deoxyribose.

Properties of Cytosine

Cytosine is a pyrimidine derivative with two substituents and a heterocyclic, aromatic ring. Organic compounds (those containing carbon) with a ring structure containing atoms with carbon, such as sulphur, oxygen, or nitrogen, as part of the ring are known as heterocyclic compounds. Aromaticity is a chemical property in which the stability of a conjugated ring of unsaturated bonds, lone pairs, or empty orbitals is greater than can be predicted from conjugation alone. A substituent is an atom or group of atoms that is substituted for a hydrogen atom on the parent chain of a hydrocarbon in organic chemistry.

Cytosine is combined with guanine in DNA and RNA. It is, however, not integrally stable and can degrade into uracil. If the DNA repair enzymes, such as uracil glycosylase, which cleaves a uracil in DNA, do not restore it, a point mutation may occur.

An enzyme called DNA methyltransferase can also methylate cytosine into 5-methylcytosine.

Cytosine Chemical Activity

Guanine and Cytosine bind together by non-covalent hydrogen bonding at three different sites, as seen in the picture. It’s worth noting that Watson and Crick first proposed that Guanine and Cytosine bonded by hydrogen bonding at two different sites.

Cytosine is a nucleotide component that can be found in DNA and RNA. Cytidine triphosphate is formed when the nucleoside cytidine binds to three phosphate groups (CTP). This molecule serves as a cofactor for enzymes, assisting in the conversion of phosphate from adenosine diphosphate (ADP) to adenosine triphosphate (ATP) in order to prepare ATP for use in chemical reactions.

Cytosine forms three hydrogen bonds with guanine in DNA and RNA. This device, however, is unstable and can transform into uracil. This is known as spontaneous deamination. If DNA repair enzymes such as uracil glycosylase do not repair the damage by cleaving uracil in DNA, a point mutation may result.

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Tautomerization in Cytosine

Tautomerization occurs when cytosine switches from amino to imino functionality through intermolecular proton transfer.

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History of Cytosine

Albrecht Kossel and Albert Neumann discovered and named cytosine in 1894 when it was hydrolyzed from calf thymus tissues. In 1903, a structure was proposed, and in the same year, it was synthesised (and thus confirmed) in the laboratory.

When Oxford University researchers introduced the Deutsch-Jozsa algorithm on a two-qubit nuclear magnetic resonance quantum computer in 1998, cytosine was used in an early demonstration of quantum information processing (NMRQC).

NASA scientists announced in March 2015 that pyrimidine can produce cytosine, uracil, and thymine under space-like laboratory conditions, which is interesting because pyrimidine has been detected in meteorites but its origin is unknown.

Purines and Pyrimidine Reaction

Purine biosynthesis differs from pyrimidine biosynthesis in that purines are formed first as a nucleotide, whereas pyrimidines are formed first as a free base. Pyrimidines are produced in a variety of tissues in humans, including the spleen, thymus, and gastrointestinal tract.

Cytosine, like other pyrimidines, is made up of several steps, the first of which is the formation of carbamoyl phosphate. A reaction involving bicarbonate, glutamine, ATP, and a water molecule produces carbamoyl phosphate. The enzyme carbamoyl phosphate synthetase catalyses the formation of carbamoyl phosphate.The catalytic activity of aspartate transcarbamylase converts the carbamoyl phosphate to carbamoyl aspartate. Following that, carbamoyl aspartate is converted to dihydroorotate, which is then oxidised to yield orotate. The ribose phosphate 5-phospho—D-ribosyl 1-pyrophosphate (PRPP) reacts with orotate to form orotidine-5-monophosphate (OMP).After that, OMP is converted into other pyrimidines. OMP decarboxylase is an enzyme that aids in the decarboxylation of OMP to produce uridine monophosphate (UMP). Kinases and dephosphorylation of ATPs eventually generate uridine diphosphate (UDP) and uridine triphosphate (UTP) further down the biosynthetic pathway. By modification of UTP with the enzyme CTP synthetase, UTP can be converted to cytidine triphosphate (CTP).

The nucleosides of cytosine are cytidine and deoxycytidine. They become cytidine triphosphate (CTP) and deoxycytidine triphosphate (dCTP), which are nucleotides that make up RNA and DNA molecules, respectively, when phosphorylated with three phosphoric acid groups.

When the pyrimidine nucleotide cytidine monophosphate (CMP) or cytosine is catabolized, the by-products -alanine, ammonia, and carbon dioxide are created. The following is the general degradation pathway: cytosine » uracil » N-carbamoyl-alanine » -alanine, carbon dioxide, and ammonia. Cytosine, on the other hand, can be recycled via the salvage pathway. Deamination, for example, can transform cytosine to uracil. Uridine phosphorylase reacts with ribose-1-phosphate to convert uracil to uridine. Uridine is converted to uridine monophosphate by the enzyme nucleoside kinase (UMP).

Mutation in Nitrogenous Bases

A mutation occurs when the nucleotide sequence of a gene or chromosome changes. A point mutation is a small-scale mutation in which only one nucleotide base in the DNA or RNA molecule changes. Cytosine is a relatively volatile substance. It has the potential to deaminate spontaneously into uracil. When this occurs in DNA, the DNA sequence is corrected by repair mechanisms. For example, uracil glycosylase is extracted from DNA by cleaving the cytosine-turned-uracil. The affected area is then removed and substituted using the other strand as a reference (i.e. the complementary strand).Base excision repair is the term for this form of procedure. In non-coding sequences, point mutations often have no discernible consequences. When it comes to coding sequences, a single nucleotide change ca
n result in incorrect decoding during protein translation, particularly if the mutation is left uncorrected. A protein’s altered structure may cause it to be unstable or non-functional, resulting in its impairment.

Biological Function of Cytosine

The other four primary (or canonical) nucleobases are thymine, uracil, guanine, and adenine. Cytosine is one of the five primary (or canonical) nucleobases. The genetic code is made up of these basic nucleobases. The genetic code for a specific protein is contained in nucleic acids such as DNA and RNA molecules, which is dependent on the sequence of nucleobases.. Nucleic acids play a crucial role in cellular functions, heredity, and organism survival. Cytosine, in the form of cytidine triphosphate (CTP), may be used as an enzyme co-factor. It can convert adenosine diphosphate (ADP) to ATP by transferring a phosphate. ATP is a high-energy molecule that is involved in a variety of cellular functions and essential biological reactions.

Difference Between Purine and Pyrimidine

The most critical distinction to understand between purines and pyrimidines is their structural differences.

Purines (adenine and guanine) have a two-ringed structure, as seen in the two diagrams below, consisting of a nine-membered molecule with four nitrogen atoms.

Purines are clearly larger than pyrimidines since they are pyrimidines fused with a second ring. Part of the explanation for complementary pairing is the size gap. Purines in DNA strands will be so large if they are bound to each other instead of the pyrimidines that the pyrimidines will be unable to enter other pyrimidines or purines on the other hand! The gap between them would be so wide that the DNA strand would be unable to hold itself together. Similarly, if the pyrimidines in DNA bonded together, the purines would run out of space.

Important Points

IUPAC name or chemical name of cytosine is 4-aminopyridine-2(1H)-one.

The chemical cytosine formula is C4H5N3O.

The molecular mass of cytosine is 111.104 g/mol.

Did You Know that?

• Cytosine is one of the 5 main nucleobases used in storing and transporting genetic information within a cell in the nucleic acids DNA and RNA. 

• Cytosine is combined with guanine in DNA and RNA. It is, however, unstable and can transform into uracil (spontaneous deamination). If not repaired by DNA repair enzymes like uracil glycosylase, which cleaves a uracil in DNA, this may result in a point mutation.

There are many topics that chemistry students have to learn to prepare for their final examinations. One of the most important topics that students have to prepare for their final examination is the derivation of the ideal gas equation. In this article, students will be able to learn the answer to questions like what is ideal gas, what are ideal gas laws, why is the ideal gas equation important, and what are some important ideal gas examples.

Let us first define ideal gas. According to experts, ideal gas can be described as a theoretical gas that comprises a set of randomly-moving point particles. These particles only interact with one another through elastic collisions. It is easy to define ideal gas, but the ideal gas meaning extends beyond that. This concept of the ideal gas formula is important as it obeys all ideal gas law equations, provides a simple equation of state, and is also amenable to analysis by employing statistical mechanisms. Further, students might be interested to note that the requirement of zero interaction can also be relaxed for an ideal gas. This ideal gas meaning is possible if interactions between all particles are perfectly elastic or regarded as simple point-like collisions.

It is almost important for students to note that under various conditions of pressure and temperature, many gases actually qualitatively behave like an ideal gas. In those cases, the ideal gas formula is somewhat bent as the gas molecules or atoms for monatomic gas play the role of ideal particles. If one relaxes the ideal gas definition a bit, then many gases like oxygen, nitrogen, noble gases, hydrogen, and some heavier gases like carbon dioxide, and a mixture of gases in the air can be treated as ideal gases. 

However, one must remember that all of this is done with reasonable tolerances to the ideal gas definition and ideal gas law equation. This is done over various parameter ranges around standard pressure and temperature. Usually, gases are more likely to behave like an ideal gas and follow the ideal gas constant at lower pressure and higher temperature. Can you take a guess as to why this happens?

The simple reason behind this is that the potential energy becomes less significant in comparison to the kinetic energy of the particles. This happens due to the intermolecular forces of attraction. Also, the size of the molecules becomes less significant, too, when compared to the empty spaces between the particles.

This concept of an ideal gas constant can also be illustrated by the fact that one mole of an ideal gas has a capacity of 22.710947(13) liters at standard pressure and temperature (S.T.P.). According to the ideal gas law formula, the standard temperature is often measured at 273.15 K, and absolute pressure is identified at 10⁵ Pa. These values have also been defined by IUPAC since 1982.

Ideal Gas Examples

The ideal gas law definition and some concepts related to the ideal gas law definition are discussed in the previous section. Hence, now we will take a look at some ideal gas law examples. Some of the common ideal gas law examples are given below. 

1. Oxygen
   

2. Nitrogen
   

3. Hydrogen
   

Ideal Gas Laws

In this section, students will be able to find out the answer to the question of what is the ideal gas law.

According to experts, ideal gas laws are laws that state the behaviour of ideal gases. These laws were primarily formulated by the observational work of Boyle in the 17th century and Charles in the 18th century. Both of these ideal gas laws are stated below.

1. Boyle’s Law: According to Boyle’s Law, if a given mass of a gas is being kept at a constant temperature, then the pressure of that gas is inversely proportional to its volume. 

2. Charles Law: This law states that for any given fixed mass of a gas that is held at constant pressure, the volume of the gas is directly proportional to its temperature.

Ideal Gas Equation

Let us look at some ideal gas equations now. The ideal gas equation is formulated as:

PV = nRT

In this equation, P refers to the pressure of the ideal gas, V is the volume of the ideal gas, n is the total amount of ideal gas that is measured in terms of moles, R is the universal gas constant, and T is the temperature.

This means that according to the ideal gas equation, the product of pressure and volume of a gas bears a constant relation (it is proportional) with the product of the universal gas constant and the temperature.

Here, the universal gas constant is denoted by R. The universal gas constant is the product of the molecular mass of any gas multiplied with the specific gas constant. According to the S.I. system, the value of the universal gas constant is 8.314 J mol^-1K^-1.

Deriving the Ideal Gas Equation

Let us assume that the pressure of a gas is ‘p,’ and the volume of the gas is ‘v.’ Also, let the temperature be ‘T,’ R is the universal gas constant, and n is the number of moles of gas. Hence, according to Boyle’s Law, if the values of n and T are kept constant, then the volume is inversely proportional to the pressure that is exerted by the gas. This can be represented as: 

V ∝ 1/P

According to Charle’s Law, if the values of p and n are kept constant, then the volume of the gas is directly proportional to the temperature. This can be represented as:

V ∝ T

According to Avogadro’s Law, if both P and T are kept constant, then the volume of the gas would be directly proportional to the number of moles of the gas. This can be represented by

V ∝ n

If we combine all the three equations, then

V ∝ n T or PV = nRT

Fun Facts About Ideal Gas

Did you know that there are three basic classes of ideal gases? These types of ideal gases are the classical or Maxwell-Boltzmann ideal gas, the ideal quantum Bose gas that is composed of bosons, and the ideal quantum Fermi gas that is composed of fermions.

Most of these gases have the same characteristics. However, there are some minute differences that students should have a clear idea of.

Tips for Students to Score Well

• Study in short intervals: Allow your brain and body to rest so you can consume the material with full energy and attention. “For every 30 minutes you study, take a short 10–15 minute break to refresh,” says Oxford Learning. Short study sessions are more efficient and allow you to maximize your study time.” Exercise boosts blood flow to the brain, giving you more energy and allowing you to concentrate better. Concentration and focus might be improved by a yoga or stretching exercise. Spending too much time on one thing might cause you to lose focus. To avoid learning fatigue, one of the most crucial study strategies for college examinations is to switch subjects every 30 minutes or so. After you’ve given your brain a pause, proceed to difficult topics. By following this technique you will be able to focus well.

• Eat healthy: To save time, students often start consuming junk food which is not the best technique for studying. Instead, feed your body with a balanced diet of “brain foods” including fresh fruits and vegetables, as well as protein and healthy fats. The same may be said about sleep: obtain a sound sleep; the night before the exam.

• Take the right approach: Different sorts of college examinations require different techniques of studying. Focusing on definitions and concepts is what multiple choice means. You must have a conceptual knowledge of the topic in essay based assessments. Inquire about the exam’s format with your professor so you know how to prepare. Go through previous years question papers as it would give an overview of the exam. Students must visit our website www.vendantu.com  if they are looking for study material.

• Test your knowledge: Create a practice test based on what you expect the test will cover once you’ve figured out the format. This will allow you to gain a better understanding of the topic and will help you choose what you should be studying. The practice test may then be used to quiz yourself and your study group. Vendantu provides students a huge question bank with solutions. These solutions are available in pdf format which make its access easier.
  

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Introduction

The Diels-Alder reaction mechanism continues via suprafacial (same face presence of the isolated orbital or the π system that exists in the process) interaction between a 4π with a 2π electron system. Diels-Alder reaction involves the cycloaddition reactions that result in the creation of a new ring from two reactants.

In the Diels-Alder reaction, the 4π electron system is referred to as the diene structure, whereas the 2π electron system is known as the dienophile structure. Now, this interaction leads to a transition state without any external energy barrier from the orbital symmetry imposition.

What is the Diels-Alder Reaction?

The Diels-Alder reaction is an essential organic chemical reaction where the reactants include a conjugated diene and a substituted alkene. Commonly, this substituted alkene is referred to as a dienophile, and this reaction gives rise to a substituted derivative of cyclohexene. The Diels-Alder reaction is such a good example of pericyclic reactions that proceed through the concerted mechanisms (it means, all bond breakage and bond formation occurs at a single step).

This reaction was discovered in 1928 by the German chemists’, Kurt Alder and Otto Diels, and for which they are awarded the Nobel Prize in Chemistry in 1950. The Diels-Alder reaction can be used to produce six-membered rings since there is a simultaneous construction of two new carbon-carbon bonds.

An illustration of the reaction between Diene and Dienophile is given below.

From the above illustration, if we observed clearly, two pi bonds were converted into two sigma bonds. This happens because of the concerted bonding of two independent pi-electron systems. Also, the Diels-Alder reaction involves the shift of four pi electrons of diene and two pi electrons of dienophile.

This reaction is used to produce vitamin B6. The reverse reaction (also known as a retro-Diels-Alder reaction) is used to produce cyclopentadiene on an industrial scale.

Mechanism of Diels-Alder Reaction

The simple mechanism of the Diels-Alder reaction is explained below.

Since the pi bonds are converted into stronger sigma bonds, thermodynamically, the reaction is favourable. The Diels-Alder reaction is favoured by the electrophilic dienophiles with electron-withdrawing groups that are attached to them. In addition, it is favoured by the nucleophilic dienes with electron-donating groups present in them. A few examples are given below for good dienes and dienophiles for the Diels-Alder reaction.

Because the Diels-Alder reaction mechanism is concerted, the reaction follows in a single step cycloaddition reaction. Here, two unsaturated molecules combine to produce a cyclic adduct. There is also a net reduction in bond multiplicity. All the bond formations and bond breakages occur simultaneously.

An example is given below on an illustration of the simple reaction mechanism.

Therefore, the diene and dienophile react to each other to form a cyclohexene derivative. It can be observed from the mechanism representation where three carbon-carbon pi bonds break, but it forms only one pi bond, and two sigma bonds are formed thereby.

Stereoselectivity of Diels-Alder Reaction

The stereoselectivity of the Diels-Alder reaction has several modifications. Where some of them are mentioned below. The stereoselectivity is also known as variations.

1. The Hetero Diels-Alder Variation

• These reactions involve either one or more heteroatoms (any atom other than hydrogen or carbon). 

• When carbonyl groups react with dienes, dihydropyran products are produced.

• The aza Diels-Alder reaction includes the use of imines as dienophile or diene substituents. The resultant product formed in this reaction is an N-heterocyclic compound.

• If a nitroso compound is used as a dienophile, the reaction resulting from the diene yields oxazines.

2. Usage of Lewis Acids

• A Lewis acid can be used as a catalyst in this variation.

• The Lewis acids examples that can be used in these reactions include boron trifluoride, aluminium chloride, zinc chloride, and tin tetrachloride.

• The electrophilicity of the dienophile complex is increased by the Lewis acid in these reactions.

• The advantages of this variation are increased reaction rates and improved regioselectivity and stereoselectivity. These types of Diels-Alder reactions can proceed at relatively low temperatures.

3. The Asymmetric Variation

In this reaction, there exist many variations that influence its stereoselectivity. The use of a chiral auxiliary is one such example. Organocatalysts with relatively small molecules can often be used to modify the stereoselectivity of this reaction.

Some significant applications of the Diels-Alder reaction include its role in the formation of vitamin B6 and its reverse-reaction role in the production of cyclopentadiene on an industrial scale.

4. Hexa Dehydro Diels-Alder

In this Hexa dehydro Diels-Alder reaction, diynes and alkynes are used instead of dienes and alkenes, forming an unstable benzyne intermediate, which then can be caught to produce an aromatic product. This reaction also allows the formation of heavily-functionalized aromatic rings in one single step.

Application of Diels-Alder reaction

The retro Diels-Alder reaction is used for the industrial production of cyclopentadiene. Cyclopentadiene is a precursor to many norbornenes, which are common monomers. Also, the Diels-Alder reaction is employed in vitamin B6 production.

A typical route for the production of ethylidene norbornene from cyclopentadiene via vinyl norbornene is represented below.