Chemical Science of CSIR Syllabus

Related tags: chemical analysis, syllabus questions, Mass spectroscopy
PAPER 1– SECTION A
1. General information on science and its interface with society to test the candidate’s awareness of science, aptitude of scientific and quantitative reasonsing.
2. COMMON ELEMENTRY COMPUTER SCIENCE ( Applicable to all candidates offering subject areas ).
3. History of development of computers, Mainframe, Mini, Micro’s and Super Computer Systems.
4. General awareness of computer Hardware i..e. CPU and other peripheral devices ( input / output and auxiliary storage devices ).
5. Basic knowledge of computer systems, software and programming languages i.e. Machine language, Assembly language and higher level language.
6. General awareness of popular commercial software packages like LOTUS, DBASE, WORDSTAR, other Scientific application packages.

PAPER 1 – SECTION B
1. Structure and Bonding : Atomic orbitals, electronic configuration of atoms ( L – S coupling ) and the periodic properties of elements ; ionic radii, ionization potential, electron affinity, electronegativity; concept of hybridization. Molecular orbitals and electronic configuration of homonuclear and heteronucelar diatomic molecules. Shapes of polyatomic molecules; VSEPR, theory. Symmetry elements and point groups for simple molecules. Bond lengths, bond angles, bond order and bond energies. Types of Chemical Bond ( weak and strong ) intermolecular forces, structure of simple ionic and covalent solids, lattice energy.
2. Acids and Bases : Bronsted and Lewis acids and bases, pH and pKa, acid-based concept in non-acqueous media ; HSAB concept. Buffer solution.
3. Redox Reactions : Oxidation numbers, Redox potential, Electrochemical series, Redox indicators.
4. Energetics and Dynamics of Chemical Reactions : Law of conservation of energy, Energy and entheipy of reactions. Entropy, free-energy, relationship between free energy change and equilibrium. Rates of chemical reactions (first-and second-order reactions). Arrhenius equation and concept of transition state. Mechanisms, including SN 1 and SN 2 reactions, electron transfer reactions, catalysis. Coiligative properties of solutions.
5. Aspects of s, p, d, f, Block Elements : General characteristics of each block. Chemical principles involved in extractions and purification of iron, copper, lead, zinc and aluminium. Coordination chemistry; structural aspects, isomerism, octahedral and tetrahedral crystal – field splitting of dorbitals. CFSE, magnetism end colour of transition metal ions. Sandwich compounds, metal carbonyls and metal clusters. Rare gas compounds, non-stoichiometric oxides. Radio activity and transmutation of elements, isotopes and their applications.
6. IUPAC Nomenciature of Simple Organic and Inorganic Compounds.
7. Concept of Chirality : Recognition of symmetry elements and chiral structures; R – S nomenciature, diastereoisomerism in acyclic and cyclic systers; E – Z isomerisms. Conformational analysis of simple cyclic ( chair and boat cyclo hexanes ) and acyclic systems. Interconversion of Fischer, Newman and Sawhorse projections.
8. Common Organic Reactions and Mechanisms : Reactive intermediates, Formation and stability of carbonium ions, carbanians, carbenes, nitrenes, radicals and arynes. Nucleophilic, electrophilic, radical substitution, addition and elimination reactions. Familiar name reactions : Aldol, Perkin, Stobbe, Dieckmann condensations; Holmann, Schmidt, Lossen, Curtius, Backmann and Fries rearrangements; Reimer – Tiemann, Reformatsky and Grignard reactions. Diels – Aider reactions; Clasien rearrangements; Friedeal – Crafts reaftions; Witting reactions; and robinson annulation. Routine functional group transformations and interconversions of simple functionalities. Hydroboration, Oppenaur oxidations; Clemmensen, Wolff-Kishner, Meerwein – Ponndorf – Verley and Birch reductions.
9. Elementary principles and applications of electronic, vibrational, NMR, EPR and Mass Spectral techniques to simple structural problems.
10. Data Analysis : Types of errors, propagation of errors, accuracy and precision, least-squares analysis, average standard deviation.

11. Statistical Tharomodynamics : Thermodynamic probability and entropy; Maxwell – Boltzmann, Bose – Einstein and Fermi – Dirac statistics. Partition function; rotational translational, vibratioanl and electronic partition functions for diatomic molecules; calculations of thermodynamic functions and equilibrium constants. Theories of specific heat for solids.
12. Non-equilibrium Thermodynamics : Postulates and methodologies, linear laws, Gibbs equation, Onsager reciprocal theory.
13. Reaction Kinetics : Methods of determining rate laws. Mechanisms of photochemical, chain and oscillatory reactions. Collision theory of reaction rates; steric factor, treatment of unimolecular reactions. Theory of absolute reaction rates, comparison of results with Eyring and Arrhenius equations, ionic reactions; salt effect. Homogeneous catalysis and Michaelis – Menten kinetics; heterogeneous catalysis.
14. Fast Reaction : Luminescence and Energy transfer processes. Study of kinetics by stopped flow technique, relazation method, flash photolysis and magnetic resonance method.
15. Macromolecules : Number – average and weight average molecular weights ; determination of molecular weights. Kinetics of polymerization. Stereochemistry and mechanism of polymerization.
16. Solids : Dislocation in solids, Schottky and Frenkel defects, Electrical properties; insulators and semiconductors; superconductors, band theory of solids, Solid-state reactions.
17. Nuclear Chemistry : Radioactive decay and equilibrium. Nuclear reactions ; Q value, cross sections, types of reactions, Chemical effects of nuclear transformations; fission and fusion, fission products and fission yields. Radioactive technique; tracer technique, neutron activation analysis, counting techniques such as G. M. ionization and proportional counter.
18. Chemistry of Non-transition Elements : General discussion on the properties of the non-transition elements; special features of individual elements; synthesis, properties and structure of their halides and oxides, polymorphyism of carbon, phosphorus and sulphur. Synthesis, properties and structure of boranes, carboranes, borazines, silicates carbides, silicones, phosphazenes, sulphur-nitrogen compounds; peroxo compounds of boron, carbon and sulphur; oxy acids of nitrogen, phosphours, sulphur and halogens, interhalogens pseudohalides and noble gas compounds.
19. Chemistry of Transition Elements : Coordination chemistry of transition metal ions ; Stability constants of complexes and their determination; stabilization of unusual oxidation states. Stereochemistry of coordination compounds. Ligandfield theory, splitting of d-orbitals in low-symmetry environments. Jahn – Teller effect; interpretation of electronic spectra including charge transfer spectra ; spectrochemical series, nephelauxetic series ,Magnetism; Dia-, para-, ferro- and antiferromagnetism, quenching of orbital angular moment, spinorbit copling, inorganic reaction mechanisms; substitution reactions, trans effect and electron transfer reactions, photochemical reaction of chromium and ruthenium complexes. Fluxional molecules iso-and heteropolyacids ; metal clusters. Spin crossover in coordination compounds.
20.Chemistry of Lanthanides and Actinides : Spectral and magnetic properties; Use of lanthanide compounds as shift reagents.
21. Organometallic Chemistry of Transition Elements : Synthesis, structure and bonding, organometallic reagents in organic synthesis and in homogeneous catalytic reactions ( hydrogenation, hydroformayalation, isomerisation and polymerization ); pl-acid metal complexes, activation of small molecules by coordination.
22. Topics in Analytical Chemistry : Adsorption partition, exclusion electrochromatography, Solvent extraction and ion exchange, methods. Application of atomic and molecular absorption and emission spectroscopy in quantitative analysis Light scattering techniques including nephelometry and Raman spectroscopy. Electroalytical techniques: voltammetry, cyclit, voltammetry, polarography, amperometry, coulometry and comductometry ion-elective electrodes. Annodic stripping voltammetry; TGA, DTA, DSC and online analysors.
23. Bioinorganic Chemistry : Metal ions in Biology, Molecular mechanism of ion transport across membranes; ionophores. Photosynthesis, PSL, PSH; nitrogen fixation, oxygen uptake proteins, cytochromes and ferrodoxins.
24. Aromaticity : Huckel’s rule and concept of aromaticty (n) annulences and heteroannulenes, fulterenes (C60).
25. Stereochemistry and conformational Analysis : Nwere method of asymmetric synthesis ( including enzymatic and catalytic nexus ), enantio and diastereo selective synthesis. Effects of conformation on reactivity in acyclic compounds and cyclohexanes.
26. Selective Organic Name Reactions : Favorskli reaction; Stork enamine reaction; Michael addition, Mannich Reaction; Sharpless asymmetric epoxidation; Ene reaction, Barton reaction, Holmann-Loffer-Freytag reaction, Shapiro reaction, Baeyer-Villiger reaction, Chichibabin reaction.
27. Mechanisms of Organic Reactions : Labelling and Kinetic isotope effects, Hamett equation, ( sigma-rho ) relationship, non-classical carbonium ions, neighbouring group participation.
28. Pericyclic Reactions : Selection rules and stereochemistry of electrocyclic reactions, cycloaddition and sigmatropic shifts, Sommelet, Hauser, Cope and Claisen rearrangements.
29. Heterocyclic Chemistry : Synthesis and reactivity of furan, thiophene, pyrrole, pyridine, quinoline, isoquinoline and indole; Skraup synthesis, Fisher indole synthesis.30. Reagents in Organic Synthesis : Use of the following reagents in organic synthesis and functional group transformations ; Complex metal hybrids, Gilman’s reagent, lithium dimethycuprate, lithium disopropylamide (LDA) dicyclohexylcarbodimide. 1,3 – Dithiane (reactivity umpolung), trimethysilyl iodide, tri-n-butyltin hybride, Woodward and provost hydroxylation, osmium tetroxide, DDQ, selenium dioxide, phase transfer catalysts, crown ethers and Merrified resin, Peterson’s synthesis, Wilkinson’s catalyst, Baker yeast.
31. Chemistry of Natural Products : Familiarity with methods of structure elucidation and biosynthesis of alkaloids, terponoids, steroids, carbohydrates and proteins.
32. Bio-organic Chemistry : Elementry structure and function of biopolymers such as proteins and nucleric acids.
33. Photochemistry : Cis – trans isomeriation, Paterno – Buchi reaction, Norrish Type I and II reactions, photoreduction of ketones, di-pimethane rearrangement, photochemistry of areanes.
34. Spectroscopy : Applications of mass, UV – VIS, IR and NMR spectroscopy for structural elucidation of compound.

Read More

Mechanism of Diels-Alder reaction

Diels-Alder reaction

This reaction was discovered by two German chemists named Otto Diels and Kurt Alder. Conjugated dienes undergo a cycloaddition reaction with multiple bonds to form unsaturated six-membered rings. This reaction involves the 1,4-addition of a diene and a dienophile. This reaction proved to be of great importance as yield was 100% and hence they received the Nobel Prize in 1950.






Reaction mechanism
The Diels-Alder reaction is a thermal cycloaddition whose mechanism involves the sigma-overlap of the pi-orbitals of the two unsaturated systems. There is not a single mechanism for all Diels-Alder reaction. At first approximation, we can divide them into two classes:

1.Synchronous and symmetrical (concerted) mechanisms when the two new bonds are formed simultaneously. In the transition state, the two forming bonds have the same lengths. The combination of ethylene and butadiene is one example.
2.Multistage (non-concerted) and asynchronous mechanisms. The transition state is a di-radical, one bond being formed, the other not.

Real mechanisms are a mixture of these two extremes, one bond being more properly formed and thus shorter than the other.
















To have an idea of the mechanism and to calculate the activation energy of a reaction, we have to find its transition state, using a gradient minimization. The transition state of the Diels-Alder addition of butadiene and ethylene shows that it looks like the reactants. It is called an early transition state.
Typically, the Diels-Alder reaction works best when either the diene is substituted with electron donating groups (like -OR, -NR2, etc) or when the dienophile is substituted with electron-withdrawing groups (like -NO2, -CN, -COR, etc).

Conformational requirements of the diene
One quirk of the Diels-Alder reaction is that the diene is required to be in the s-cis conformation in order for the Diels-Alder reaction to work. The s-cis conformation has both of the double bonds pointing on the same side of the carbon-carbon single bond that connects them. In solution, the carbon-carbon single bond in the diene that connects the two alkenes is constantly rotating, so at equilibrium there is usually some mixture of dienes in the s-trans conformation and some in the s-cis conformation. The ones that are at that moment in the s-trans conformation do not react, while the ones in the s-cis conformation can go on to react.






Because of the Diels-Alder's requirement for having the diene in a s-cis conformation, dienes in rings react particularly rapidly because they are "locked" in the s-cis conformation. Unlike dienes in open chains in which there is usually some proportion of the diene in the unreactive s-trans conformation, dienes in rings are held in the reactive conformation at all times by the constraints of the ring, making them react faster.







Stereochemistry of Diels-Alder reaction
If the dienophile is disubstituted (substituted twice), there is the possibility for stereochemistry in the product. In the Diels-Alder reaction, you end up with the stereochemistry that you started with. In other words, if the substituents started cis (on the same side) on the dienophile, they end up cis in the product. If they started trans (opposite sides) on the dienophile, they end up trans in the product.

Read More

Photochromic materials

Photochromic materials


Photochromic molecules can belong to various classes: triarylmethanes, stilbenes, azastilbenes, nitrones, fulgides, spiropyrans, naphthopyrans, spiro-oxazines, quinones.




Spiropyrans and Spriooxazines

Spiro-mero photochromism.
One of the oldest, and perhaps the most studied, families of photochromes are the spiropyrans.

Very closely related to these are the spirooxazines.

For example, the spiro form of an oxazine is a colorless leuco dye; the conjugated system of the oxazine and another aromatic part of the molecule is separated by a sp³-hybridized "spiro" carbon. After irradiation with UV light, the bond between the spiro-carbon and the oxazine breaks, the ring opens, the spiro carbon achieves sp² hybridization and becomes planar, the aromatic group rotates, aligns its π-orbitals with the rest of the molecule, and a conjugated system forms with ability to absorb photons of visible light, and therefore appear colorful. When the UV source is removed, the molecules gradually relax to their ground state, the carbon-oxygen bond reforms, the spiro-carbon becomes sp³ hybridized again, and the molecule returns to its colorless state.

This class of photochromes in particular are thermodynamically unstable in one form and revert to the stable form in the dark unless cooled to low temperatures. Their lifetime can also be affected by exposure to UV light. Like most organic dyes they are susceptible to degradation by oxygen and free radicals. Incorporation of the dyes into a polymer matrix, adding a stabilizer, or providing a barrier to oxygen and chemicals by other means prolongs their lifetime.

Diarylethenes

Dithienylethene photochemistry

The "diarylethenes" were first introduced by Irie and have since gained widespread interest, largely on account of their high thermodynamic stability. They operate by means of a 6-pi electrocyclic reaction, the thermal analog of which is impossible due to steric hindrance. Pure photochromic dyes usually have the appearance of a crystalline powder, and in order to achieve the color change, they usually have to be dissolved in a solvent or dispersed in a suitable matrix. However, some diarylethenes have so little shape change upon isomerization that they can be converted while remaining in crystalline form.

Photochromic quinones

Some quinones, and phenoxynaphthacene quinone in particular, have photochromicity resulting from the ability of the phenyl group to migrate from one oxygen atome to another. Quinones with good thermal stability have been prepared, and they also have the additional feature of redox activity, leading to the construction of many-state molecular switches that operate by a mixture of photonic and electronic stimuli.

Inorganic photochromics

Many inorganic substances also exhibit photochromic properties, often with much better resistance to fatigue than organic photochromics. In particular, silver chloride is extensively used in the manufacture of photochromic lenses. Other silver and zinc halides are also photochromic.

Fulgides

Triarylmethanes

Triphenylmethane, or triphenyl methane, is the hydrocarbon with the formula (C6H5)3CH. This colorless solid is soluble in nonpolar organic solvents, but not water. Triphenylmethane has the basic skeleton of many synthetic dyes called triarylmethane dyes, many of them are pH indicators, and some display fluorescence. A trityl group in organic chemistry is a triphenylmethyl group Ph3C, e.g. triphenylmethyl chloride — trityl chloride

Examples of triarylmethane dyes are bromocresol green or malachite green

Read More