Sky Of Chemistry

There are different ways of classifying them  1 st classification: Depending upon whether the polymer contains the atoms of only one element or of different elements in its backbone, they are classified into the following two groups. [1] Homo-atomic polymers: These polymers contain the atoms of only one element in their backbones Silicon, phosphorus, sulphur, germanium and tin from homo-atomic inorganic polymer. For example, sulphur has a tendency to form chains or rings in its elemental form (S 8 ) and in several compounds, like persulphides (H-S-S-H, H-S-S-S-H, H-S-S-S-S-H etc.) [2] Hetero-atomic Polymers: These contain the atoms of different elements in their backbones 2 nd Classification Inorganic polymers can also be classified in another way, which is base on the type of reaction by which the polymers are formed. On this basis, inorganic polymers may be of the following types: [1] Condensation (polymerisation) polymers. Condensation polymers are those, which are formed by t...

All the covalent macromolecules, which do not have carbon in their back bones are considered to be inorganic polymers. Inorganic polymers  are  polymers  with a skeletal structure that does not include carbon atoms in the backbone. ... The term  inorganic polymer  refers generally to one-dimensional  polymers , rather than to heavily crosslinked materials such as silicate minerals. Example : Crystals (e.g. oxides and halides), condensed. These polymers posses distinctive physicochemical characteristics and unique physical, mechanical and electrical properties. These polymers are of extensive utility in everyday life, particularly in the area of engineering and technology.

Fluorescence  When a beam of light is incident on certain substances, they emit visible light or on radiations and they stop emitting light or radiations and they stop emitting light or radiation as soon as the incident light is cut off. This phenomenon is known as fluorescence . The substance that exhibit fluorescence are known as fluorescent substances. When a substance absorbs light energy, electrons move from inner orbits to outer orbits. When these excited electrons return to the ground state, the light is emitted. This emitted light may possess a different frequency than the incident light. X (Normal state) + hv (Photon) ⟶ X* (Excited state) X* ⟶ X** + hv' X** ⟶ X + hv" Where X** represents an energy state between X and X*. The emitted radiation frequencies v' And v" are different from v, the frequency of incident radiation. Some Characteristics of fluorescence: (i) This phenomenon is instantaneous and starts immediately after the absorption of light and stops ...

Luminescence Usually, light is obtained by heating solids or solid particles to high temperatures. By heating a tungsten(W), platinum wire or carbon filament electrically or in a flame, bright light can be obtained. The phenomenon in which thermal energy is converted into the light is known as 'incandescence'. When the emission of visible radiation occurs due to some cause other than temperature, the phenomenon is known as 'Luminescence'. Light is produced at low temperatures, so it is also known as cold light. In both incandescence and luminescence, light is emitted due to the return of electrons from the exciting position to a lesser excitation position or ground state.  Classification of Luminescence 1. Photoluminenscence :  Luminescence caused by light is called photoluminescence. Photoluminescence that stops immediately as soon as the incident light is cut off is called fluorescence. Photoluminescence that continues for an appreciable time even after the incident l...

Factors Affecting Quantum yield [1] Temperature :   The change of quantum yield with temperature is given by the equation d(logΦ)/dT = Q/RT 2 Where Φ is quantum yield and Q is the amount of heat evolved by the formation of a one-mole substance. Photochemical decomposition of ammonia increases by about 15% for every 100ํ ℃ temperature increase. It reaches seven-fold by 500 ℃. [2] Wavelength :   As frequency increases, the power of light energy increases, so quantum yield increases. In other words, the quantum yield decreases as wavelength increases. [3] Light Intensity: As light intensity decreases, quantum yield increases. [4] Inert gases: The addition of inert gases increases the quantum yield. This is because inert gases increase the number of starting chains as they may retard the diffusion of the atoms to the walls. This effect will decrease the rate of the chain-terminating steps. Thus, the rate of reaction increases thereby quantum yield increases.

Class - I: High quantum yield reactions. Reactions in which quantum yield is greater than unity are high quantum yield reactions. The quantum yield of the combination of carbon monoxide and chlorine by the light of a wavelength from 4000 to 4360 Å is 10 3 . CO + Cl 2 ➝ COCl 2 The quantum yield of the combination of hydrogen and chlorine by the light of wavelength less than 4500 Å is 10 4 to 10 6  H 2 + Cl 2 → 2HCl Photochemical decomposition of H 2 O 2 by a wavelength of about 3100 Å has a quantum yield of more than 7. 2H 2 O 2 → 2H 2 O + O 2    Class - II: Low quantum yield reactions. Reactions in which quantum yield is less than unity are low quantum yield reactions. The quantum yield of the combination of hydrogen and bromine to form HBr is about 0.01 H 2 + Br 2 → 2HBr The quantum yield of photolysis of ammonia by a wavelength 2100 Å is nearly 0.2 2NH 3 → N 2 + 3H 2 Class - III: Small integer quantum yield reactions. Reac...

A photochemical reaction involves two processes. One is the  primary process in which light is absorbed by molecules to give excited molecules. Another is a  secondary process in this process exciting molecule initiates a series of thermal reactions. In such reactions, many reactant molecules may undergo chemical change by absorbing one quantum only. In some cases, the activated molecule undergoes deactivation. Thus, less than one molecule may react per quantum. The overall result of the photochemical reaction is expressed in terms of Quantum yield.  The quantum yield or efficiency(Φ) is defined as: " It is the number of molecules which undergo chemical transformation per quantum of absorbed energy. " Mathematically, Φ = No. of molecules reacting in a given time/ No. of quanta absorbed in the same time Φ = No. of moles reacting in a given time/ No. of Einsteins absorbed in the same time Φ = Rate of chemical reaction/ No. of Einsteins absorbed  The quantum yields ar...

Laws of Photochemistry (1) Grotthuss-Draper law (First Law of Photo-chemistry): Only the light which is absorbed by a molecule can be effective in producing photochemical changes in the molecule. "When light y on any substance, only the fraction of incident light which is absorbed by the substance can bring about a chemical change, reflected and transmitted light do not produce any such effect." This law is purely qualitative. It doesn't give any relationship between the amount of light absorbed by a system and the number of molecules reacted. (2) Stark-Einstein's Law (Second Law of Photo-chemistry): "It states that for each photon of light absorbed by a chemical system, only one molecule is activated for a photochemical reaction." Einstein applied quantum theory to photochemical reactions and gave the law. " When an atom or molecule absorbs light of a given frequency, it absorbs one quantum only" The energy absorbed by one mole of the reacting mol...

When light is incident upon a homogeneous medium, a part of the incident light is reflected, a part is absorbed and the rest is transmitted. I 0 = I a + I t + I r                                                                        ...........................(1) Where, I 0 = Incident light             I a = Absorbed light             I t = Transmitted light             I r = Reflected light. Ir is very small, so eq.(1) becomes, I 0 = I a + I t                                                                    ......................(2) Lambert's...

Thermochemical(Dark) Reactions Photochemical Reactions (1) It involves absorption or evolution of heat. (1) It involves absorption of light. (2) It can occur in dark as well as in light. (2) Presence of light is a must. (3) Temperature has a significant effect on the rate of reaction. (3) Temperature has very little effect on the rate of reaction. (4) These reactions are always accompanied by a decrease in free energy. In these reactions,   free energy may increase or decrease. (5) Activation energy is obtained by intermolecular collisions. (5) Activation energy is obtained by a particular type of radiation. (6) Thermal excitation increases in a random manner. i.e. translational, rotational and vibrational energy of all the molecules increases. (6) By selecting a particular type of radiation particular at...

Introduction Photochemistry is the study of chemical effects produced by light radiations ranging from 2000 to 8000 Å wavelength. Type of Chemical Reaction: A chemical reaction is one in which, the identity of molecules is changed due to the breaking and formation of chemical bonds. There are two types of chemical reactions. (i) Dark or Thermal reaction: The reaction which is influenced by temperature, the concentration of reactants, catalyst etc. except light radiations are known as thermal reactions. N 2 + 3H 2 ⇌ 2NH 3 H 2 + I 2     ⇌ 2HI (ii)Photochemical Reactions: The reaction which is influenced by the action of light is known as photochemical reactions.  Some examples are following, 2HBr ⟶ H 2 Follow us on Social media for the latest information about the blog.👇👇

The Bischler–Napieralski synthesis This synthesis was first suggested by Bischler and Napieralski and has been subjected to a number of improvements later on. This method involves the cyclodehydration of an acyl derivative of B-phenylethylamine to give 3,4-dihydro isoquinoline, in the presence of Lewis acids such as polyphosphoric acid, zinc chloride or phosphorous pentoxide. The 3,4-dihydro isoquinoline is then dehydrogenated by Pd( Palladium ) at 160°C to Isoquinoline. It must be noted that the yield of this reaction is excellent if electron-donating groups are present on the benzene ring however if the electron-withdrawing groups are present on the benzene ring the yields are very poor. This is because of the electrophilic ring closure nature of the ring.

Isoquinoline Isoquinoline is a heterocyclic aromatic organic compound. It is a structural isomer of quinoline. Isoquinoline is also obtained by ring fusion of pyridine and with a benzene ring. It was first isolated by Hoogewerff and Drop from the quinoline fraction of coal tar in 1885. Several derivatives of Isoquinoline also occur in coal tar. Isoquinoline does not occur free in nature but founds frequently in several alkaloids. It is called 2-azanaphthalene or benzo[b]pyridine. The numbering of the atoms in Isoquinoline is similar as followed in quinoline; however, the nitrogen atom is assigned position-2. Isoquinoline has close similarities in the structure with quinoline; therefore both have a close relationship in their physical and chemical properties.

This is one of the most important methods for preparation of quinoline. In this method the aniline and its derivatives having vacant ortho position is when heated with glycerol, concentrated H2SO4 and an oxidizing agent the resultant product is obtained as quinoline or its derivatives. The nitrobenzene is generally used as mild oxidizing agent in Skraup synthesis. Glycerol when heated with concentrated H2SO4 it gives the acroline after dehydration. Condensation of acroline thus obtained with aniline or its derivatives followed by oxidation gives the quinoline. The reaction is shown follow. Mechanism: The step wise mechanism of Skraup synthesis of quinoline is given as follow.

Quinoline Quinoline is a heterocyclic aromatic organic compound with the chemical formula C9H7N. It is a colourless hygroscopic liquid with a strong odor. It is also called 1-azanaphthalene or phenazopyridine.  Quinoline was first extracted from coal tar in 1834 by German chemist Friedlieb Ferdinand Rung; he called quinoline leukol ("white oil" in Greek). Coal tar remains the principal source of commercial quinoline. In 1842, French chemist Charles Gerhardt Obtained a compound by dry distilling quinine., strychnine, or chinchonine with potassium hydroxide; he called the compound Chinoilin or Chinolein. Runge's and Gephardt's compounds seemd to be distinct isomers beacuse they reacted differently. However, the German chemist August Hoffmann eventually recognized that the differences in behaviors were due to the presence of contaminants and that the two compounds were actually identical. Like other nitrogen heterocyclic compounds, such as pyridine derivatives, quino...

Reduction of Pyridine Under catalytic hydrogenation of pyridine hexahydro pyridone is formed. It is also known as Piperidine.

Basicity of Pyridine, Pyrrole From Experimental studies, it is observed that the pKb values of Pyrrole, Pyridine and Piperidine are ~14, ~8.7 and ~2.7, respectively. Based on the suggested pKb values the priperidine in found as a stronger base than pyridine and pyrrole. Pyrrole is the weakest base among these three heterocyclic bases. The order of basicity of pyrrole, pyridine and piperidine is as given below: The above order of basicity of pyrrole, pyridine and piperidine can be justified in terms of the structure of these compounds. As we know that the basicity of nitrogen compounds depends upon the availability of lone pair of electrons on the nitrogen atoms. In pyrrole, the lone pair of electron on nitrogen atom exists in the sp2 hybridized orbital of nitrogen and participates in the delocalization, hence does not freely available to cause the basic character of pyrrole. Similar to pyrrole, the lone pair of electrons on the nitrogen atom of pyridine also exists in the...

Nucleophilic Substitution Reactions of Pyridine As we have discussed in the previous section that pyridine generally deactivated the aromatic ring towards electrophilic substitution reaction. The deactivation of the aromatic rings towards electrophilic substitution resulted due to the electron-withdrawing nature of the nitrogen atoms. Due to such deactivation, Pyridine also gives nucleophilic substitution reaction. Nucleophilic substitution in pyridine ring occurs at position C-2. Approach of the nucleophilic at position C-2 leads to the formation of three resonating structures(I, II and III); similarly, the approach of nucleophilic at position C-3 also leads to the formation of three resonating structures (IV, V and VI). The resonating structures for intermediate resulting from the attack of the nucleophile at position C-2 are more stable than those of position C-3 since more electronegative nitrogen atoms hold a -ve charge in one of the resonating structures (III) obtained from th...

Electrophilic substitution in Pyridine Pyridine is also an aromatic compound. It is less aromatic than benzene and pyrrole. Pyridine is usually considered a highly deactivated aromatic nucleus towards electrophilic substitution reactions. Therefore highly vigorous reaction conditions should be used for these reactions to take place. The low reactivity of pyridine towards the electrophilic substitution reactions is due to the following reasons: The higher electronegativity of the nitrogen atom reduces electron density on the ring, thus deactivate the ring. Pyridine is highly sensitive to acidic medium; it readily forms pyridinium cation with a positive charge on the nitrogen atom. Similarly, electrophile itself may also react with pyridine from the corresponding pyridinium ion. This positive charge on the nitrogen atom decreases the electron density of the nitrogen atom, consequently, the electron density on the ring also decreases. However, the effect of such deactivation is c...

Pyridine Structure of Pyridine : The structure of Pyridine is completely analogous to that of benzene, being related by replacement of CH by N. The key differences are : (i) the going away from perfectly regular hexagonal geometry caused by the presence of the heteroatom, in particular the shorter carbon-nitrogen bonds, (ii) the replacement of a hydrogen in the plane of the ring with an unshared  electron pair, likewise in the plane of the ring, located in an sp2 hybrid orbital and not at all involved in the aromatic π - electron sextet; It is this nitrogen lone pair which is responsible for the basic properties of Pyridines, and (iii) a strong permanent diople,  discovered to the greater electronegativity of nitrogen compared with carbon. It is important to realise that the electronegative nitrogen causes inductive polarisation, mainly in the σ - bond framework, and additionally stabilize those polarised mesomeric contributors in which nitrogen is neg...