Molecular orbital studies of hydrogen-bond directed aggregation and crystal formation.
Item
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Title
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Molecular orbital studies of hydrogen-bond directed aggregation and crystal formation.
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Identifier
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AAI9417512
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identifier
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9417512
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Creator
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Turi, Laszlo.
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Contributor
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Adviser: Joseph J. Dannenberg
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Date
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1994
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Language
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English
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Publisher
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City University of New York.
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Subject
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Chemistry, Physical
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Abstract
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Ab initio and semiempirical molecular orbital calculations have been performed for the crystal formation of four molecules: 1,3-cyclohexanedione, acetic acid, para-nitroaniline and meta-nitroaniline. Hydrogen bonding interactions are shown to be the primary structure determinants in these crystals via (a) strong hydrogen bonding cooperativity and (b) C-H{dollar}\...{dollar}O interactions. Hydrogen bonding cooperativity explains not only the significant geometry changes of the individual molecules within the crystal lattice compared to the gas or liquid phase structures but often dictates the H-bonding network of the crystalline phase, as for 1,3-cyclohexanedione. All the examined cases illustrate the importance of C-H{dollar}\...{dollar}O hydrogen bonds in determining the crystal structure. This influence is especially important in the stacking phenomenon of acetic acid and m-nitroaniline crystals. In the latter case, C-H{dollar}\...{dollar}O H-bonds provide the extra stabilization necessary to overcome the unfavorable electrostatic effects of the head-to-head chain orientation that leads to non-centrosymmetric crystal structure and nonlinear optical properties. High level ab initio calculations on small molecular complexes of HCN and H{dollar}\sb2{dollar}C{dollar}\sb2{dollar} with water, formaldehyde and ozone also support the existence and significance of C-H{dollar}\...{dollar}O interactions.;I found very good correlation between the calculated and experimental crystal structures. The semiempirical AM1 method proved to be especially impressive for estimating heat of sublimation values, reproducing experimental geometries or unit cell parameters.;It was concluded that empirical potential functions based on two-body interactions are not very likely to be useful for studying crystal formation, biological systems or any related problem where strong cooperative (non-additive) effects might arise.;For ab initio calculations on molecular complexes containing more than two molecules, a simple counterpoise procedure for correcting the basis set superposition error is examined and proposed.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
