12 Noncovalent Molecular Forces

Organic Chemistry: Structure and Function

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1 Noncovalent Molecular Forces - Part 1 Lecture Supplement: Take one handout from the stage
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2 Chemistry 14C Part 3 Structure Controls Everything Physical properties Boiling point Solubility etc. Chemical properties Reactions Reactivity Biological properties Drug effects etc. + Salt enhances water solubility Ring strain allows irreversible enzyme inhibition Influence antibiotic behavior xample: Penicillin G (an antibiotic) N S O O Na O N O H
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3 Noncovalent Molecular Forces tive forces (other than covalent bonding) between atoms or molecules hould I study this? Noncovalent forces control association of molecule which causes Physical properties: melting point, boiling point, solubility, e Molecular organization into larger structures: membranes, e Molecular recognition: substrate/enzyme docking, etc.
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4 How Do We Measure Noncovalent Forces? nsider evaporation of water... Evaporation add energy Water vapor Liquid water Attractive force keeps molecules close nger attractions = more energy required to break = more energy needed for evaporation = higher boiling point ng point is useful approximation of attractive forces ng point easily measured Noncovalent attractive force disrupted Covalent bonds still intact
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5 How Do We Measure Noncovalent Forces? point: temperature at which vapor pressure of substance = ambient pre point: influenced by... tive forces al packing Ambiguous measure of attractive forces } What Kinds of Noncovalent Forces Occur? Consider these substances: NaCl bp 1413 o C H 2 O bp 100 o C BrF bp 20 o C Ar bp -186 o C Increasing magnitude of attractive forces
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6 NaCl bp 1413 o C = Na + = Cl - hat attractive force is operating? hat is the nature of association between Na and Cl? Cl Na EN 3.0 0.9 N = 3.0 - 0.9 = 2.1 ractive force = ionic bond = cation-anion = electrostatic (opposite charges attract) aporation or melting = separating opposite charges Cl evaporates as Na + and Cl - not NaCl Cl heat of vaporization = 188 kcal mol -1 gh bp and mp typical of ionic compounds
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7 Ionic versus Covalent Bonds mical bond = sharing of electron pair c bond: highly unequal sharing of electron pair alent bond: approximately equal sharing of electron pair Increasing EN
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  • Atom, Chemical bond, attractive force, Noncovalent

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