School of Chemistry

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    Polarized Optical Absorption Studies on Copper and Silver Diethyldithiocarbamates
    ( 1976-11-01) Rajasekharan, M. V. ; Sethulakshmi, C. N. ; Mancharan, P. T. ; Gudel, Hans
    Polarized optical absorption measurements are reported for bis(N,N-diethyldithiocarbamato)copper(II) and -silver(II) diluted in the corresponding zinc complex. The measurements have been made at room, liquid nitrogen, and helium temperatures. The results for the copper complex are at variance with those reported earlier by Reddy and Srinivasan. The electronic transition energies are used in conjunction with the previously reported spin-Hamiltonian parameters to derive the molecular orbital coefficients for the two complexes. © 1976, American Chemical Society. All rights reserved.
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    A new 1,2-shift in the oxidation of aromatic rings
    ( 1977-01-01) Periasamy, M. ; Bhatt, M. Vivekananda
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    1,2-Shift in the anodic oxidation of aromatic compounds
    ( 1979-01-01) Bhat, Gajanan A. ; Periasamy, Mariappan ; Vivekananda Bhatt, M.
    The 1,2-shift observed during oxidation of organic substrates can arise by involvement of cation radicals. © 1979.
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    Crystal and Molecular Structure of two Crystalline Modifications of Bis[1-methyl-3-(2-chloro-6-methylphenyl)triazine 1-oxidato]nickel(II), NiBPT-a Bis Chelate with a Five-Membered Ni-N-O Ring
    ( 1979-02-01) Rajasekharan, M. V. ; Manoharan, P. T. ; Varughese, K. I.
    The title compound is obtained in two different crystalline modifications. The green elongated parallelepiped crystals obtained from acetone solutions belong to the monoclinic space group P21/a with Z = 4, a = 14.306 (3) Å, b = 7.858 (1) Å, c = 18.605 (3) Å, β = 103.72 (3)°, dcalcd= 1.489 g/cm3, and dmeasd= 1.50 g/cm3. A benzene solvate, NiBPT-C6H6, belonging to the space group P1 is obtained from benzene solutions and has Z = 1, a = 7.9637 (9) Å,b = 9.246 (2) Å, c = 9.999 (2) Å, α = 63.93 (1)°, β = 77.44 (1)°, γ = 68.57 (1)°, dcalcd= 1.442 g/cm3, and dmeasd= 1.42 g/cm3. The structures of both crystals were determined by using three-dimensional diffractometer data. In the case of NiBPT, full-matrix least-squares refinement using 2731 reflections having I > 2σ(I) led to a conventional R value of 0.071. For NiBPT-C6H6the refinement using 1523 reflections having I > 3σ(I) converged to an R value of 0.032. The coordination in the NiN202moiety is strictly planar in both modifications with Ni-0 and Ni-N distances of 1.849 (4) and 1.846 (6) Å, respectively, and a N-Ni-O angle of 83.4 (2)°. (The values are averaged over the two structure determinations. The root-mean-square value of the esd's in individual measurements is given in parentheses.) The benzene molecule in the solvated crystal is situated too far from the nickel atom to have any appreciable interaction with it. The analogous cobalt complex, CoBPT, is shown to be isomorphous with NiBPT. © 1979, American Chemical Society. All rights reserved.
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    An X-ray study of strontium bromate monohydrate
    ( 1980-01-01) Sastry, D. L. ; Rajasekharan, M. V. ; Rao, K. V.S.Rama
    Preliminary X-ray data on Sr(BrO3)2· H2O show that the crystal belongs to the monoclinic system with four molecules per unit cell. The unit cell dimensions are a = 8.8742, b = 7.609, c = 9.3748, β = 91.27°. The space group is I2/c-C62h. © 1980, Akademische Verlagsgesellschaft.
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    EPR STUDIES ON COPPER AND COBALT TRIAZENE-1-OXIDE COMPLEXES IN A FROZEN NEMATIC MEDIUM.
    ( 1980-01-01) Rajasekharan, M. V. ; Manoharan, P. T.
    EPR spectra of copper and cobalt complexes of certain triazene-1-oxide ligands were measured in frozen nematic liquid crystal glasses in order to identify the principal directions of the magnetic interaction tensors. It is pointed out that the nature of solute alignment is primarily determined by its molecular shape and any chemical interaction between the metal complex and the functional groups of the solvent molecules. Once these factors are properly understood, oriented glass spectra can be used to identify the principal axes of the g and A tensors even for systems which deviate considerably from gross molecular planarity. The spin Hamiltonian parameters are discussed on the basis of the ligand field model. It is pointed out that all the cobalt complexes reported here have the unpaired electron in the d//y//z orbital.
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    Structural Effects in Solvolytic Reactions. 36. Effect of Increasing Electron Demand on Carbon-13 Nuclear Magnetic Resonance Shifts in the 1-Aryl-1-cyclohexyl and 1-Aryl-1-cycloheptyl Carbocations. Further Test of the Ability of the σ < sup > c+ < /sup > Constants to Correlate Carbon-13 Nuclear Magnetic Resonance Shifts
    ( 1981-01-01) Brown, Herbert C. ; Periasamy, Mariappan
    The 13C NMR shifts of a series of meta- and para-substituted 1-phenyl-1-cyclohexyl and 1-phenyl-1-cycloheptyl carbocations were measured in SbF5/FSO3H/SO2CIF at -80 °C to provide a further test of the ability of the new set of σC+ constants to correlate such 13C NMR shifts. Indeed, the data reveal excellent linear correlation of the observed shifts, ∆δC+, in these two systems by the σC+ constants. The 1-aryl-l-cyclohexyl system yields a ρc+ value of -17.2, with a correlation coefficient of r = 0.999. The 1-aryl-1-cycloheptyl system gives ρC+ = -16.4, with r = 0.999. Previous investigation of the 1-aryl-1-cyclopentyl system yielded ρC+ = -16.8, with r = 0.999. Thus all of the systems containing five-+, six-, and seven-membered rings are correlated with satisfactory precision by the values. The variation in pc from the five-, to the six-, to the seven-membered systems parallels the changes in ρ+ observed in solvolysis of the p-nitrobenzoates. However, the variations with ring size are larger in the solvolytic studies. It is concluded that both ground-state energies and the electronic stabilization of the cations are enhanced in the five- and seven-membered rings, contributing to the change in ρ+ from that observed for the six-membered ring. On the other hand, differences in ground-state energies can play no role in the magnitude of ρC+ for the fully formed carbocations. © 1981, American Chemical Society. All rights reserved.
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    Structural Effects in Solvolytic Reactions. 38. Carbon-13 Nuclear Magnetic Resonance Studies of Carbocations. 6. < sup > 1 < /sup > Effect of Increasing Electron Demand on the Chemical Shifts of the α-Carbon Atoms in Substituted Aryldialkyl Carbocations. Correlation of the Data with a New Set of Substituent Constants, σ < sup > αC+ < /sup >
    ( 1981-01-01) Brown, Herbert C. ; Kelly, David P. ; Periasamy, Mariappan
    With increasing electron demand, the 13C NMR shifts of the α-carbons, the carbon atoms adjacent to the cationic center (C+), undergo significant downfield shifts. However, the substituent chemical shifts, ∆δCα, for the α-carbon atoms (CH3) of substituted tert-cumyl cations are not correlated either by the σ+ or the σc+ constants. Plots of ∆δCα against σ+ and of ∆δCα against σC+ reveal that the points for the para derivatives deviate systematically from the lines defined by the data for the meta derivatives. These deviations indicate that a new set of para substituent constants, one intermediate in value between the σp+ and σpC+ constants, is needed to correlate satisfactorily the -carbon chemical shifts for the para derivatives. Accordingly, such a set of substituent constants, σαC+, was estimated by using the slope (-4.1) of the line defined by a plot of ∆δCα for the meta derivatives σm+ to satisfy the Hammett-type equation ∆δCα = ραC+ σαC+. The utility of these new σαC+ constants to correlate chemical shift data for the a positions of substituted benzylic cations was tested with the data for the α different systems. Indeed, very good correlations were observed when the chemical shifts for these systems are plotted against these σαC+ values: 2-aryl-2-butyl, r = 0.997, ρ(CH2)αC+ = -4.1, r = 0.998, ρ(CH3)αC+ = -4.0; 3-aryl-3-pentyl, r = 0.999, ραC+ = -3.9; 4-aryl-4-heptyl, r = 0.994, ραC+ = -3.6; 1-aryl-1-cyclopentyl, r = 0.999, ραC+ = -4.9; 1-ary 1-1-cyclohexyl, r = 0.998, ραC+= -4.9; 1-ary-1-1-cycloheptyl, r = 0.999, ραC+ = -4.7; 9-aryl-exo-5,6-trimethylene-9-norbornyl, r = 0.999, ραC+ = -4.1; 9-aryl-endo-5,6-trimethylene-9-norbornyl, r = 0.998, ραC+ = -4.4; 2-aryl-2-adamantyl, r = 0.993, ραC+ = -5.9. The trend in the ραC+ values in these cations is discussed. © 1981, American Chemical Society. All rights reserved.
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    Structural Effects in Solvolytic Reactions. 35. Carbon-13 Nuclear Magnetic Resonance Studies of Carbocations. Effect of Increasing Electron Demand on the Carbon-13 Nuclear Magnetic Resonance Shifts in 2-Aryl-2-butyl and 4-Aryl-4-heptyl Carbocations. Correlation of the Data by a New Set of Substituent Constants, σ < sup > C < /sup > < sup > + < /sup >
    ( 1981-01-01) Brown, Herbert C. ; Periasamy, Mariappan ; Liu, Kwang Ting
    The 13C NMR shifts of a series of meta- and para-substituted 2-phenyl-2-butyl and 4-phenyl-4-heptyl carbocations were measured in SbF5/FSO3H/SO2ClF. The plots of the chemical shifts of the cationic carbon, ∆δC+, in the various substituted derivatives against the values of substituent constants, π and π+, reveal only relatively poor correlations. However, excellent linear correlations are realized in the plots of ∆δc+ against the new σC+ values proposed for these systems. The 2-aryl-2-butyl system yields a pC+ value of -17.78 with a correlation coefficient r = 0.9998. The 4-aryl-4-heptyl system gives a pC+ value of -14.57 with r = 0.999. The nearly perfect linear correlations observed for these systems support the validity and utility of these new σC+ constants. © 1981, American Chemical Society. All rights reserved.
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    Structural Effects in Solvolytic Reactions. 37. Effect of Increasing Electron Demand on Carbon-13 Nuclear Magnetic Resonance Shifts in the 9-Aryl-exo-5,6-trimethylene- and 9-Aryl-endo-5,6-trimethylene-9-norbornyl Carbocations. Effect of the Cationic Carbon Center on Remote Carbon Atoms in the Skeleton As Revealed by Increasing Electron Demand
    ( 1981-01-01) Brown, Herbert C. ; Periasamy, Mariappan
    The 13C NMR shifts of a series of meta- and para-substituted 9-phenyl-exo-5,6-trimethylene-9-norbornyl and 9-phenyl-endo-5,6-trimethylene-9-norbornyl carbocations were measured in SbF5/FSO3H/SO2ClF at -80 °C. Excellent linear correlations were realized in the plots of ∆δC+ against the σc+ constants. The 9-aryl-exo-5,6-trimethylene-9-norbornyl system yields a pc+ value of -16.3 with a correlation coefficient of 0.999. The 9- aryl-endo-5,6-trimethylene-9-norbornyl system gives a ρc+ value of -15.9 with a correlation coefficient of 0.999. In addition, the data reveal some unusual effects of the cationic center on the remote carbon atoms in the skeleton. For example, the Cδ carbon in the 9-aryl-endo-5,6-trimethylene-9-norbomyl system undergoes an upfield shift of 1.5 ppm from the p-OCH3 to the p-CF3 substituent, as compared to the downfield shifts (or no shifts) observed for the Cα, Cβ, and Cγ carbons in simple aryldialkyl carbocations. Possible reasons for such upfield shifts with electron demand are discussed. © 1981, American Chemical Society. All rights reserved.
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    Triquinanes : synthesis and transformations
    (University of Hyderabad, 1981-09-29) Srikrishna, A. ; Mehta, Govardhan
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    Matrix dependent polycrystalline E.P.R. spectra and analysis of forbidden hyperfine lines in the single crystal E.P.R. spectra of triazene-1-oxide complexes of cobalt(II)
    ( 1981-12-10) Rajasekharan, M. V. ; Manoharan, P. T.
    The influence of the matrix or lattice on the E.P.R. parameters of some triazene-1-oxide complexes of cobalt(II) has been investigated by detailed computer simulations of polycrystalline and frozen glass spectra. Also reported here are single crystal E.P.R. results for these complexes in nickel host lattices. The unambiguous determination of orientation of the magnetic tensor components with respect to the molecular axes, relative signs of the hyperfine coupling parameters and the analysis of forbidden transitions based on a complete diagonalization of the spin hamiltonian brings out the importance of both the quadrupolar and nuclear Zeeman contributions. © 1981 Taylor & Francis Group, LLC.
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    Structural Effects in Solvolytic Reactions. 40. Carbon-13 Nuclear Magnetic Resonance Studies of Carbocations. 8. Anomalous Carbon-13 Chemical Shifts with Increasing Electron Demand in the 2-Aryl-2-norbornyl Cations and Related Systems. Evidence That These Anomalous Shifts Are Not Diagnostic for the Onset of Nonclassical σ Bridging
    ( 1982-01-01) Brown, Herbert C. ; Periasamy, Mariappan ; Kelly, David P. ; Giansiracusa, Joseph J.
    13C NMR spectra of an extended range of 2-aryl-2-norbornyl (11), 2-aryl-exo-5,6-trimethylene-2-norbornyl (12), 2-aryl-endo-5,6-trimethylene-2-norbornyl (13), 3-aryl-3-nortricyclyl (14), 1-aryl-1-cyclopropylethyl (15), 1-aryl-1-phenylethyl (28), and 1-aryl-1-phenylmethyl (29) carbocations have been obtained under standard conditions. When the cationic carbon substituent chemical shifts Δδ C+ are plotted against the new δ C+ constants, the points for the substituents more electron donating than H (Z = 3′4′-CH2CH2O to Z = H) yield excellent linear correlations, whereas those for substituents more electron demanding than H (Z = H to Z = 3′,5′-(CF3)2) curve away from this correlation line. These deviations from linearity are in contrast to the plots for a large range of static, classical acyclic (1–4), cyclic (5–7), and polycyclic (8–10) carbocations, which yield excellent correlations of Δδ C+ with σ C+. The deviations in the plots for 11 and 12 have been rationalized previously in terms of the onset of σ bridging, for 14 in terms of the onset of increased cyclopropyl conjugation and for 28 in terms of steric inhibition of resonance. However, examination of our data shows that for each of the three different molecular structures, 2-norbornyl (11–13), cyclopropylcarbinyl (14, 15), and phenylalkyl (28, 29), the same, in fact, almost identical, deviations are observed. In addition, the aryl derivatives of other cationic systems for which σ -bridged structures have been proposed, cyclobutyl (19), 2-bicyclo[2.1.1]hexyl (20), 2-bicyclo[2.2.2]octyl (21), and 6-bicyclo[3.2.1]octyl (22), fail to exhibit such deviations with the data available. Thus we conclude that the anomalous 13C shifts, which give rise to the deviations from linearity in the plots of Δδ C+ against σ C+ (or Δδ C+, cyclopentyl), are not diagnostic for the onset of nonclassical σ bridging. Possible explanations for these anomalous C+ shifts are considered. © 1982, American Chemical Society. All rights reserved.
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    A General Synthesis of B-(cis-1-Bromo-1-alkenyl)dialkylboranes. Valuable Intermediates for the Synthesis of Ketones, Trans Alkenes, and Trisubstituted Alkenes
    ( 1982-01-01) Brown, Herbert C. ; Basavaiah, D.
    Dialkylboranes, generated in situ via hydridation of dialkylhaloboranes, hydroborate 1-bromo-1-alkynes to provide cleanly B-(cis-1-bromo-1-alkenyl)dialkylboranes. Treatment of these intermediates with sodium methoxide results in the migration of one of the alkyl groups on boron to the adjacent carbon, displacing the bromine, providing B-(trans-1-alkyl-1-alkenyl)alkylborinate esters. These intermediates provide ketones on oxidation, stereospecific trans alkenes on protonolysis, and trisubstituted alkenes on iodination, all in high yields. © 1982, American Chemical Society. All rights reserved.
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    Structural Effects in Solvolytic Reactions. 42. Effect of Increasing Electron Demand on the Carbon-13 Nuclear Magnetic Resonance Shifts for Substituted 9-Methyl-9-anthracenium Cations. Evidence for the Unimportance of Steric Hindrance to Coplanarity in Causing Anomalous Carbon-13 Nuclear Magnetic Resonance Shifts
    ( 1982-01-01) Brown, Herbert C. ; Periasamy, Mariappan
    A series of substituted 9-methyl-9-anthracenium cations were prepared in FSO3H/SO2ClF at −78 °C and their 13C NMR shifts were measured at −80 °C. The Δ℘C+ shifts observed for the electron-donating substituents correlate linearly against the aC+ constants. However, the data observed for the electron-withdrawing substituents deviate upward from the straight line defined by the data of electron-donating substituents, similar to the deviation observed for the 1-aryl-1-phenyl-1-ethyl carbocations. The deviation observed in the latter case was previously attributed to steric inhibition of coplanarity. However, comparison of the behavior of this system with that of the 9-methyl-9-anthracenium system casts doubt upon this explanation. © 1982, American Chemical Society. All rights reserved.
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    Structural Effects in Solvolytic Reactions. 41. The Effect of Coplanarity on the Carbon-13 Nuclear Magnetic Resonance Shifts of Substituted o-Methyl-tert-cumyl Cations
    ( 1982-01-01) Brown, Herbert C. ; Periasamy, Mariappan
    The effect of steric inhibition on coplanarity was examined by preparing a series of 4/5-substituted o-methyl-tert-cumyl carbocations in SbF6/FSO3H/SO2ClF at −78 °C and measuring their 13C NMR shifts at −80 °C. The ΔδC+ shifts correlate linearly against the σC+ constants with a ρC+ value of −18.3 and a correlation coefficient of 0.9995. The excellent correlation observed for this system indicates that the deviations in the σC+-ΔδC+ plots observed for certain systems of benzylic carbocations are probably not the result of steric hindrance to coplanarity in these systems. The ρC+ value of −18.3 is essentially the same as the value of −18.2 observed for the substituted tert-cumyl cations. This indicates that the fully developed dimethylcarbinyl cationic center must be able to overcome the steric difficulties in achieving coplanarity with the aromatic ring with only minor costs in energy, in contrast to the situation in the solvolysis of related derivatives. © 1982, American Chemical Society. All rights reserved.
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    A Stereospecific Synthesis of Trisubstituted Alkenes via Hydridation of Dialkylhaloboranes Followed by Hydroboration-Iodination of Internal Alkynes
    ( 1982-01-01) Brown, Herbert C. ; Basavaiah, D. ; Kulkarni, Surendra U.
    Dialkylvinylboranes, prepared conveniently via the hydridation of dialkylhaloboranes in the presence of an internal alkyne, react with iodine under basic conditions to produce trisubstituted alkenes of established stereochemistry, providing a general synthesis of trisubstituted alkenes with unambiguous stereochemistry. © 1982, American Chemical Society. All rights reserved.