111 questions from the UPSC 2020 examination.
111 questions
Generally alkyl halides are soluble in non-polar solvents and insoluble in water but cycloheptatrienyl bromide is insoluble in non-polar solvents but readily soluble in water. Explain this unusual behaviour of cycloheptatrienyl bromide.
Consider the following opposing reaction: A <=> B (both are elementary) with k1/k2 = 2. Depict the plots of concentration of A and B as a function of time and explain.
Show that a surface catalysed decomposition reaction follows zero order kinetics with respect to reactant when its pressure is high enough.
Identify the product and the name reaction involved in the following conversion. Also write the mechanism involved offering suitable explanation for the choice of CH3SO3H for this reaction : [Reaction scheme]
The complex [Ni(CN)4]^2- is diamagnetic, but [NiCl4]^2- is paramagnetic and has two unpaired electrons. Explain these observations and deduce the structure of two complexes.
Cerium (III) ion with 4f^1 electronic configuration is colorless while cerium (IV) ion having 4f^0 electronic configuration is red. Explain.
Match Column-I (Cycloadditions) with Column-II (Hückel-Möbius systems) using PMO approach : Column-I I : [2s + 2s] II : [4s + 2a] III : [4s + 2s] IV : [2a + 2s] Column-II A = An, M, hv-allowed B = A, H, delta-allowed C = A, M, delta-allowed D = An, H, hv-allowed where An = Antiaromatic, A = Aromatic, M = Möbius, H = Hückel, delta = Thermally, hv = Photochemically.
Identify the product and briefly discuss the steps involved in the following reaction : [Reaction scheme]
Identify the product and the name reaction involved in the following conversion. Also write the mechanism involved offering suitable explanation for the choice of CH3SO3H for this reaction : (Includes reaction scheme with CH3SO3H / Dichloroethane)
Offer an explanation for your choice of rate-determining step.
Identify X and Y in the following reactions and outline the mechanism for the formation of X in both the reactions : (Includes reaction (ii) with NNHTs, n-BuLi, H3O+)
Phenol and water are partially miscible liquids. By mixing these two liquids, we get two phases in equilibrium. Find the number of degrees of freedom of the system and mention them with the help of its phase diagram.
The quantum yield for photo decomposition of HI(g) at wavelength 254 nm is 1.99. If a total of 3070 J of energy is absorbed then how many moles of HI(g) decomposed?
3-Buten-2-one gives two peaks in its ultraviolet spectrum at 213 nm (epsilon = 7100) and 320 nm (epsilon = 27). What type of transition is responsible for each absorbance? Account for the difference in molar absorptivity for the two absorptions.
Although carbon and magnesium are both common elements in the human body, Grignard reactions do not occur in cells. Why is it so?
What are metastable ions and how are they formed? The mass spectrum of toluene shows strong molecular ion peak at m/z 91 and its fragment at m/z 65. Calculate the value for metastable ion peak.
A person claims that a heat engine exchanges heat with reservoirs at 300 and 500 K, produces 450 J of work per 1000 J of heat extracted from the hot reservoir. Is his/her claim feasible? Give reason(s) to support your answer.
Which reaction is the fastest? Briefly explain.
In the crystal structure of CuF2, the Cu2+ is six-coordinated with four F- at a distance of 1.93 A and two F- at 2.72 A. Explain the reason(s) for this.
Calculate the magnetic moment of gadolinium (III) ion (in BM units).
What does most probable speed (Cmp), average speed (Cav) and root mean square speed (Crms) mean? Indicate these speeds on a Maxwell distribution curve. What does the area under the Maxwell distribution curve represent?
Complete the following conversion writing missing intermediate compounds A, B and C : [Reaction sequence diagram]
To eliminate liquid-junction potential, KCl-salt bridge is used, generally. Does it eliminate liquid-junction? If not, how salt-bridge eliminates liquid junction potential?
Complete the following reaction sequence by identifying the missing intermediates/products/reagents as the case may be. Explain the chemistry of each step by writing detailed mechanism involved. Also identify the name reaction involved : [Reaction scheme]
The equilibrium constant for the reaction : Fe3+(aq) + Ag(s) <=> Fe2+(aq) + Ag+(aq); is 0.531 at 298 K. Calculate E°Ag+(aq)/Ag(s) when E°Fe3+(aq)/Fe2+(aq) = 0.770 V at 298 K.
Starting with methylcyclohexane, how could you prepare the following vicinal trans-dihalide? [Diagram showing a cyclohexane ring with a methyl group and two bromine atoms]
An organic compound X was erroneously assigned the following structure : [Structure X] The spectral data of the organic compound are given below. On the basis of the spectral data, justify why X is definitely a wrong structure and write the correct structure compatible with the spectral data : IR (cm^-1) : 1705, 1604 1H NMR : delta_H (ppm) 1.43 (s, 6H), 5.82 (s, 1H), 7.35 (m, 3H), 7.68 (m, 2H) MS : m/z 188 (10%) (high resolution confirms C12H12O2), 105 (20%), 102 (100%), 77 (20%)
Complete the conversion given below writing intermediate steps involved : [Conversion scheme]
What does most probable speed (C_mp), average speed (C_av) and root mean square speed (C_rms) mean? Indicate these speeds on a Maxwell distribution curve. What does the area under the Maxwell distribution curve represent?
Dichloromethane has a chemical shift of 532 Hz from TMS (tetramethylsilane) on a 100 MHz spectrometer. What will be the chemical shift in ppm? What would the chemical shift be in ppm and Hz on a 600 MHz spectrometer?
Write the name of the following complexes using the IUPAC nomenclature : (i) [Co(NH3)6] Cl3, (ii) Na2[ZnCl4], (iii) [Pt(Py)4][PtCl4], (iv) [(NH3)5Co-NH3-Co(NH3)5](NO3)5, (v) AIK(SO4)2 . 12 H2O
How will you prepare building block of the polymer PTFE starting with CH4 (g)? List the applications of PTFE.
Predict the major product, and identify the type and stereochemical mode of the following reaction : (Includes a chemical reaction scheme with a diene/triene and delta at 130 °C)
Arrange the following compounds in increasing order of out of plane C-H wagging vibrations, as shown, and give a suitable explanation to justify your answer : (Includes four benzene derivative structures labeled A, B, C, D)
Why SiH3 - NCS is linear, whereas CH3 - NCS is bent?
(i) A reaction completes in twice the time of its half-life period. What is the order of the reaction? Give reason(s). (ii) Show that for a first order reaction, the time required for 99.9% completion is almost 10 times the time for 50% completion.
An organic compound X was erroneously assigned the following structure : (Includes a structure for X) The spectral data of the organic compound are given below. On the basis of the spectral data, justify why X is definitely a wrong structure and write the correct structure compatible with the spectral data : IR (cm^-1): 1705, 1604 1H NMR : δH (ppm) 1.43 (s, 6H), 5.82 (s, 1H), 7.35 (m, 3H), 7.68 (m, 2H) MS : m/z 188 (10%) (high resolution confirms C12H12O2), 105 (20%), 102 (100%), 77 (20%)
Which methyl group would exhibit a higher chemical shift in 1H NMR spectrum?
Predict the approximate chemical shift values for both the methyl groups.
Write down the respective electrode reactions, cell reaction and Nernst equation for cell EMF of the following galvanic cell : Zn(s) | ZnCl2(aq) | Hg2Cl2(s) | Hg(l)(Pt)
Complete the following reaction giving the structures of intermediates involved : [Reaction scheme]
Identify the kinetically favoured product from the reaction given below. Justify your choice of the product : [Reaction scheme with A, B, C, D]
Write the name of the following complexes using the IUPAC nomenclature: (i) [Co(NH3)6] Cl3, (ii) Na2[ZnCl4], (iii) [Pt(Py)4][PtCl4], (iv) [(NH3)5Co-NH3-Co(NH3)5](NO3)5, (v) AlK(SO4)2 . 12 H2O
The ionic radii of Na+, K+ and Br- are 137, 148 and 195 pm, respectively. Determine the coordination number and geometry of cations in NaBr and KBr.
Compare the length of an α-helix that contains 74 amino acids with that of a B-DNA having same number of base pairs. Also mention if the lengths of these biopolymers increase or decrease on denaturation.
3-Buten-2-one gives two peaks in its ultraviolet spectrum at 213 nm (ε = 7100) and 320 nm (ε = 27). What type of transition is responsible for each absorbance? Account for the difference in molar absorptivity for the two absorptions.
Identify how vibrational spectroscopy might be used to monitor the progress of the following reaction : [Reaction scheme]
Match Column-I (Cycloadditions) with Column-II (Hückel-Möbius systems) using PMO approach : (Includes Column-I with [2s+2s], [4s+2a], [4s+2s], [2a+2s] and Column-II with An, M, hv-allowed etc.)
Identify X and Y in the following reactions and outline the mechanism for the formation of X in both the reactions : (i) [Reaction 1] (ii) [Reaction 2]
An orthorhombic unit cell has the following parameters : a = 0.5 A, b = 1.0 A, c = 1.5 A. What will be the smallest spacing between two successive 123-planes?
Express heat capacity at constant volume (Cv) of a substance in terms of its internal energy (U) and show that (dCv/dV)_{T,n} = 0; for ideal gas.
Show that half-life period (t1/2) of the following parallel reaction is ln(2) / (k1 + k2). A -> (k1) B, A -> (k2) C (Both reactions are elementary).
(i) Why are manganese, iron or cobalt used in redox enzymes in preference to zinc, gallium and calcium? (ii) Explain the emergence of Ca2+, Zn2+ and Cu2+ in the control of protein folding rather than Al3+ or Cr3+. (iii) State the characteristics of Zn2+ that make it suitable as the metal ion in many hydrolytic enzymes. (iv) What features of manganese suit it to function as a redox centre in PS-II as opposed to metals such as copper or nickel?
A compound has molecular formula C5H10, showing absorption at 1380 cm^-1. Identify the structure of the compound.
Complete the conversion given below writing intermediate steps involved : (Includes tetrabromobenzene reacting with I-, hv)
Define carbonium ion. Is it identical or different with respect to carbocation? Explain giving suitable examples.
Complete the following reaction sequence by identifying the missing intermediates/products/reagents as the case may be. Explain the chemistry of each step by writing detailed mechanism involved. Also identify the name reaction involved : (Includes reaction scheme starting with an amine and LDA)
What type of hybridization is expected for SO3^2- and PF5 ? Explain the shapes of these molecules.
d-d electronic transition forbidden? Why are they weakly absorbing and why do they occur at all?
Identify X and Y in the following reactions and outline the mechanism for the formation of X in both the reactions : (Includes reaction (i) with Me3Si and mCPBA followed by H3O+)
Identify the compounds A and B in the following reaction sequence : [Reaction sequence]
The wave function of the hydrogen atom is given by R1s = 1/sqrt(pi) e^-r (in atomic units). What will be the most probable distance of an electron from the nucleus in its ground state (in unit of a0, the Bohr radius and in Å unit) ?
Predict the major and minor products in the following reaction and give a suitable explanation : [Reaction scheme for 2-Fluoropentane + CH3O-]
What is the major product of the fastest reaction? Explain briefly.
In the crystal structure of CuF2, the Cu2+ is six-coordinated with four F- at a distance of 1.93 Å and two F- at 2.72 Å. Explain the reason(s) for this.
Solid sulphur on heating in an open container melts, but solid iodine sublimes. Explain why.
Identify the compounds A, B and C in the following conversions : (Includes reaction scheme (i) with NBS, OH-, KMnO4, HIO4)
Calculate van der Waals constants for ethylene. Given : critical temperature (Tc) = 282 K and critical pressure (Pc) = 50 atm.
What is LCAO? What are bonding, non-bonding and anti-bonding orbitals? Illustrate with a suitable diagram with an example of H2 molecule within the framework of molecular orbital (MO) theory.
Identify the kinetically favoured product from the reaction given below. Justify your choice of the product : (Includes reaction of 1,3-cyclohexadiene with Br2)
Identify the compounds A, B and C in the following conversions : (Includes reaction scheme (ii) with alkene, OsO4, Pb(OAc)4)
The dissociation energy decreases on going from N2 to N2+ whereas it increases on going from O2 to O2+. Explain.
Offer a suitable explanation to justify your choice of methyl group.
Describe the steps involved in the following reaction : (Includes cyclobutane derivative with hv followed by ROH)
Predict the major product, and identify the type and stereochemical mode of the following reaction : [Reaction scheme with a reactant, delta/130 C conditions]
Write the kinetic as well as thermodynamic product(s) of the reaction of DBr with 1,3-cyclohexadiene. Which product (kinetic or thermodynamic) would be formed more readily at higher temperature? Identify the more stable product and justify your choice of the more stable product.
Identify the compounds A and B in the following reaction sequence : (Includes reaction scheme with NaBH4, MeOH, LiAlH4, H3O+)
Consider the following opposing reaction : A <=> (k1 over k2) B (both are elementary) Depict the plots of concentration of A and B as a function of time and explain. Given : k1/k2 = 2
Discuss all the possible decay routes of an electronically excited molecule with the help of a neat Jablonski diagram.
Write down Debye-Huckel limiting equation for i^th type of ionic species in a salt solution with symbolic significances and units.
Show that half-life period (t_1/2) of the following parallel reaction is ln(2) / (k1 + k2) (Both reactions are elementary).
Identify the compounds A, B and C in the following conversions : (i) [Reaction sequence 1] (ii) [Reaction sequence 2]
Describe the steps involved in the following reaction : [Reaction scheme]
Using appropriate fundamental equation of thermodynamics, derive the following Maxwell relation : (dS/dP)_{T,n} = -(dV/dT)_{P,n}
Complete the following reaction giving the structures of intermediates involved : (Includes reaction scheme with hv, Py, Mesitol)
Write down Debye-Huckel limiting equation for ith type of ionic species in a salt solution with symbolic significances and units.
Calculate C=O stretching frequency, K = 12.3 x 10^5 dyne/cm.
What would be the sign; negative, positive or zero; for dH, dS and dG for the process of spontaneous adsorption of gas on solid surface at constant temperature. Give reasons.
(i) What is inorganic benzene? Write down its structural formula. (ii) What is the order of reactivity of the following interhalogens? ClF3, IF7, ClF, BrF5, IF
Mention the reagent(s) and write the mechanism for the following conversion : (Includes chemical structure conversion)
Mention the reagent(s) and write the mechanism for the following conversion : [Conversion scheme]
Compare the length of an alpha-helix that contains 74 amino acids with that of a B-DNA having same number of base pairs. Also mention if the lengths of these biopolymers increase or decrease on denaturation.
A spherical soap bubble of volume pi/6 cm^3 stands suspended in air. If the interfacial tension for soap solution-air interface is 27 dyn cm^-1, calculate the excess pressure inside the bubble.
Predict the major and minor products in the following reaction and give a suitable explanation : (Includes reaction of 2-fluoropentane with CH3O- / CH3OH)
(i) What is inorganic benzene? Write down its structural formula. (ii) What is the order of reactivity of the following interhalogens? CIF3, IF7, CIF, BrF5, IF
Arrange the following compounds in increasing order of out of plane C-H wagging vibrations, as shown, and give a suitable explanation to justify your answer : [Structures A, B, C, D]
Identify how vibrational spectroscopy might be used to monitor the progress of the following reaction : (Includes reaction of an alcohol with conc. H2SO4)
The rate constant for the reaction of diphenylchloromethane with pyridine and triethylamine is same. Write the structure of the major product in the following reaction. Justify your answer : [Reaction scheme]
The wave function of the hydrogen atom is given by R1s = 1/sqrt(pi) e^(-r) (in atomic units). What will be the most probable distance of an electron from the nucleus in its ground state (in unit of a0, the Bohr radius and in A unit)?
Complete the following conversion writing missing intermediate compounds A, B and C : (Includes a reaction arrow scheme)
Calculate C=O stretching frequency, K = 12.3×10^5 dyne/cm.
The rate constant for the reaction of diphenylchloromethane with pyridine and triethylamine is same. Write the structure of the major product in the following reaction. Justify your answer : (Includes reaction scheme with diphenylchloromethane and NEt3)
An orthorhombic unit cell has the following parameters : a = 0.5 Å, b = 1.0 Å, c = 1.5 Å. What will be the smallest spacing between two successive 123-planes?
Write a detailed curved arrow mechanism of the fastest identified reaction and identify the rate-determining step of your mechanism.
Why are d-d electronic transition forbidden? Why are they weakly absorbing and why do they occur at all?
Identify the product and briefly discuss the steps involved in the following reaction : (Includes reaction scheme with SOCl2, CH2N2, AgNO3)
Explain the phenomenon of capillary action with showing relation between the angle of contact and the nature of liquid and derive the expression, gamma = 1/2 hpgr (Symbols have usual meanings).
What would be the sign; negative, positive or zero; for Delta H, Delta S and Delta G for the process of spontaneous adsorption of gas on solid surface at constant temperature. Give reasons.
1.0 mol of a monoatomic ideal gas expands to double of its initial volume against a constant pressure under isothermal condition of 300 K. Calculate the heat involved.
Starting with methylcyclohexane, how could you prepare the following vicinal trans-dihalide? (Includes a chemical structure of trans-1,2-dibromo-1-methylcyclohexane or similar)
What do you mean by degeneracy of energy level? Find the number of degeneracy of hydrogenic orbital having energy - R_H / 36. R_H = Rydberg constant.