srinivasan kuduva - Academia.edu (original) (raw)

Papers by srinivasan kuduva

Hawley's Condensed Chemical Dictionary, 2007

Acta Crystallographica Section C Crystal Structure Communications

Acta Crystallographica Section C Crystal Structure Communications, 1999

The title compound, C 20 H 24 O 3 , was obtained as a by-product in the reaction of pinacolone an... more The title compound, C 20 H 24 O 3 , was obtained as a by-product in the reaction of pinacolone and 4-iodoanisole. The crystal structure was determined at 120 (2) K. The molecule is bisected by a mirror plane (space group Pnma). Comment The title compound was obtained as a by-product in the reaction of pinacolone and 4-iodoanisole. Data were collected out to theta = 24.40 and it is observed that this is slightly less than recommended in Notes to Authors. Experimental Pinacolone and 4-iodoanisole were reacted in the presence of potassium tert-butoxide in dimethyl sulfoxide solution and stirred for 3 h in the dark at room temperature. Refinement Higher angle data were of insignificant intensity.

Crystal Engineering, 1998

Structural studies currently underway in our group are reported in this paper. Molecular symmetry... more Structural studies currently underway in our group are reported in this paper. Molecular symmetry is rarely carried over into the crystal, posing problems when high-symmetry networks are desired. This is illustrated by the lowsymmetry structure of 2,4,6-trinitromesitylene. However, the involvement of the Cl 3 supramolecular synthon ensures a hexagonal network structure for 2,4,6-tris-(4-chlorophenoxy)-1,3,5-triazine. Arguments following from the equivalence between molecular and supramolecular synthons lead to the tetragonal network structure of the 1:1 complex of tetraphenylmethane and CCl 4. With a similar reasoning, 4-(triphenylmethyl)benzoic acid is identified as a precursor of a supramolecular wheel-and-axle host substance. The study of novel and weaker intermolecular interactions is often useful. In N,NЈdibenzyl-1,4-cubanedicarboxamide, the acidity of the cubyl C-H groups leads to the formation of C-H⅐⅐⅐O hydrogen bonds. Polymorphism is a difficult challenge for the crystal engineer and, in its most intriguing manifestation, two crystalline forms of a substance appear in the same crystallization batch. This is observed for 4,4-diphenyl cyclohexadienone. The ultimate frontier in the subject is an understanding of the phenomenon of crystallization, and the unexpected crystal structure of quinoxaline, with five symmetry-independent molecules, could possibly represent a case of arrested crystallization.

Tetrahedron Letters, 1998

The title compound crystallises from several aromatic solvents to produce wheel-and-axle host-gue... more The title compound crystallises from several aromatic solvents to produce wheel-and-axle host-guest complexes. The crystal structures and inclusion properties of the xylene and chlorobenzene solvates are discussed.

Structural Chemistry - STRUCT CHEM, 2001

The crystal structure of 4-cyanocubanecarboxylic acid contains the same syn–anti carboxyl group c... more The crystal structure of 4-cyanocubanecarboxylic acid contains the same syn–anti carboxyl group catemer that is found in other cubane monocarboxylic acids. The cyano groups are arranged according to the type-II geometry, in that they are 21 screw-axis related. Curiously, there is a 5% orientational disorder of the cyano and anti carboxyl groups. The ester of the title acid packs isostructurally with the corresponding chloro and fluoro analogs because of the importance of the C—H...O hydrogen bond patterns. 1,4-Dicyanocubane forms solid solutions with 1,4-dibromocubane, but, interestingly, the crystal structure of the solid solution is distinct from that of either component. The formation of these solid solutions seems to be governed by shape and size factors.

Journal of the American Chemical Society, 1999

A family of 4-substituted-1-cubanecarboxylic acids have been synthesized and their X-ray crystal ... more A family of 4-substituted-1-cubanecarboxylic acids have been synthesized and their X-ray crystal structures analyzed. The rare syn-anti O-H‚‚‚O catemer 6 is a recurring pattern in this series of compounds. Catemer 6 is observed in the crystal structures of 4-chloro-1-cubanecarboxylic acid (10), 4-bromo-1cubanecarboxylic acid (11), 4-iodo-1-cubanecarboxylic acid (12), and 4-(methoxycarbonyl)-1-cubanecarboxylic acid (13). The ready occurrence of catemer 6 in this family is ascribed to its stabilization by auxiliary C-H‚‚‚O hydrogen bonds formed by the relatively acidic cubyl C-H groups. The frequency of occurrence of 6 also facilitates its definition as a useful supramolecular synthon. As is true in many catemers, the formation of 6 is sensitive to steric factors. Therefore, the robustness of this synthon may be assessed by analyzing the crystal structures of molecules wherein the 4-substituent is too small (R) H, 14), too large (R) Ph, 15), or has a specific hydrogen bonding preference of its own (R) CONH 2 , 16). In these structures, either dimer 3 (in 14 and 15) or heterodimer 22 (in 16) is observed. Powder diffraction shows that the previously noted structure of 1,4-cubanedicarboxylic acid (7) that contains catemer 6 is characteristic of the bulk material. In summary, the syn-anti catemer is the dominant supramolecular synthon in this family of cubanecarboxylic acids.

Journal of Physical Organic Chemistry, 2000

ABSTRACT The generally higher melting-point of a para-disubstituted benzene relative to the corre... more ABSTRACT The generally higher melting-point of a para-disubstituted benzene relative to the corresponding meta-isomer has been ascribed to the fact that, being more symmetrical, it can pack more tightly. Exceptionally, it was observed that whereas m-anisylpinacolone melts at 58.0 °C, the para-isomer melts lower at 39.5 °C. In this work we have attempted to understand this apparent anomaly. The crystal structures of both isomers were determined and the packing analysed. Energy calculations of the static structures and molecular dynamics (MD) simulations at temperatures just below the respective melting-points were performed. The structure analyses indicate that the intermolecular contacts are comparably weak in the two cases, and do not appear to be the direct cause of the melting-point difference. Thermal motion analysis, packing energies and MD simulations on minicrystals indicate the importance of both enthalpic and entropic factors in the melting behaviour of the two isomers. The higher melting point of the meta-isomer could originate from both a smaller ΔSf and higher ΔHf relative to the para-isomer. Copyright © 2000 John Wiley & Sons, Ltd.

The Journal of Organic Chemistry, 2001

The unusual N-H‚‚‚O hydrogen bond pattern in a family of primary cubanecarboxamides is described.... more The unusual N-H‚‚‚O hydrogen bond pattern in a family of primary cubanecarboxamides is described. 4-Chloro-1-cubanecarboxamide, 1, and the corresponding bromo and iodo derivatives, 2 and 3, form the "shallow-glide" hydrogen-bonded motif instead of the usual 5.1 Å translated ribbon pattern, more characteristic of primary amides. This behavior is also seen, somewhat unexpectedly, for cubanecarboxamide, 4, but more or less unsurprisingly for 1,4-cubanedicarboxamide, 5. This repetitive occurrence of the same hydrogen bond pattern is of significance in crystal engineering wherein synthon robustness is measured in terms of such repetitivity. The cubyl group is directly responsible for the appearance of the shallow-glide motif in this family in preference to the 5.1 Å translation pattern for two reasons: (1) stericsit is too large to fit in a 5.1 Å translated structure and (2) electronicsits carbon acidity is sufficient to result in the appearance of C-H‚‚‚O hydrogen bonds to the CdO group, disrupting any putative 5.1 Å translated structure. Such a molecule f supermolecule relationship is of value in crystal engineering strategies.

Acta Crystallographica Section E Structure Reports Online, 2002

Journal of the Chemical Society, Perkin Transactions 2, 1999

Seven pseudopolymorphs of 3,5-dinitrosalicylic acid are studied. Four of these (A-D) are obtained... more Seven pseudopolymorphs of 3,5-dinitrosalicylic acid are studied. Four of these (A-D) are obtained from dioxane and their formation is rationalised on the basis of simultaneous O-H ؒ ؒ ؒ O and C-H ؒ ؒ ؒ O bond formation between the donor-rich solute molecule and the multiple-acceptor solvent. A fifth (E) is a previously reported centrosymmetric hydrate. The sixth and seventh (F and G) are a non-centrosymmetric hydrate and a tert-butyl alcoholate whose structures are related to that of form E, in that hydrogen bonds are both donated and accepted between solute and solvent. The formation of this rich diversity of pseudopolymorphs with hydrogen bonding solvents follows from the nature of the title acid while the similarities between the structures of the pseudopolymorphs may be accounted for in terms of a permutation of a small number of solute-solvent supramolecular synthons. All this indicates that this interesting phenomenon may be both anticipated and also studied systematically. The scope of the term pseudopolymorph has been extended a little, in the expectation that such a definition would be of more general utility.

Chemical Communications, 2002

The evolution of crystal engineering into a form of supramolecular synthesis is discussed in the ... more The evolution of crystal engineering into a form of supramolecular synthesis is discussed in the context of problems and opportunities in the pharmaceutical industry. Specifically, it has become clear that a wide array of multiple component pharmaceutical phases, so called pharmaceutical co-crystals, can be rationally designed using crystal engineering, and the strategy affords new intellectual property and enhanced properties for pharmaceutical substances.

Chemical Communications, 2005

J. Chem. Soc., Dalton Trans., 2002

ABSTRACT The preparation of the monostibines o-Me2TTF–SbPh2 (1) and Me3TTF–SbPh2 (2), the ortho d... more ABSTRACT The preparation of the monostibines o-Me2TTF–SbPh2 (1) and Me3TTF–SbPh2 (2), the ortho distibine o-Me2TTF(SbPh2)2 (3) and the tetrastibine TTF(SbPh2)4 (4) is described together with their electrochemical properties and the X-ray crystal structures of the neutral 1 and 3. In the former, one intermolecular SbS contact completes the co-ordination sphere of the antimony atom while in 3 the TTF moieties stack on top of each other with no evidence for SbS interactions. Electrocrystallisation of 2 in the presence of [n-Bu4N]2[Mo6O19] affords a 2 ∶ 1 salt, [2]2[Mo6O19] where the 2+˙ cation radical species are associated into diamagnetic [2]22+dyads through a strong HOMOHOMO overlap interaction, separated from each other by the [Mo6O19]2− counter ions.