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1、( Intermolecular Forces ) 之物质结构（3）分子间作用力Dr. Xiaogai Yang Department of Chemical BiologySchool of Pharmaceutical SciencesPeking UniversityEmail: How Drug works - A majority of pharmacologic responses are mediated through receptors-Weak Interactions Are Crucial to Macromolecular Structure and Function
2、 云云腾致腾致雨雨 露露结为结为霜霜Molecular polarityMolecular polarityInstantaneous dipolePermanent dipoleIntermolecular forces are electrostatic forces. Intermolecular forces are electrostatic forces. The Origination of Intermolecular Forces Types of Intermolecular ForcesOrientation ForceInduction ForceLondon Disp
3、ersion ForceH-BondingIon-Dipole ForcesHydrophobic InteractionsOrientation ForceDipole Dipole ForcePolar moleculePolar moleculeInduction ForceDipole Induced Dipole ForcePolar moleculePolar moleculePolar moleculeNonpolar moleculeLondon Dispersion ForceInduced Dipole Induced Dipole ForcePolar moleculeP
4、olar moleculePolar moleculeNonpolar moleculeNonpolar moleculeNonpolar moleculePolarizabilityDispersion force tends to increase with increasing molecular massSummaryOrientation ForceInduction ForceDispersionForcePolar moleculePolar moleculePolar moleculeNonpolar moleculeNonpolar moleculeNonpolar mole
5、culevan der Waals Forces分子偶极矩（实）/10-30Cm取向力/kJmol-1诱导力/kJmol-1色散力/kJmol-1总分子间作用力/kJmol-1沸点/KHI1.400.0250.11325.8726.00HBr2.670.690.50221.9423.11206.2HCl3.603.311.0016.8321.14189.2分子间作用能的分配ExerciseExerciseB.P. increase with the M.W. increasingExceptionException：HH2 2O, HF O, HF 和和NHNH3 3WHY WHY ? ?Ex
6、cept for van der Waals forces, there must be some other force氢键 (H-Bonding)X XH-H-Y YNOFFNO极性共价键an unshared electron pairOne of the smaller atoms-X相同-Y相同-X,Y均相同-A hydrogen bond is an attractive interaction between an unshared electron pair on an electronegative O, N, and F and a positively polarized
7、 hydrogen atom bonded to another O, N, or F.high boiling pointslow boiling points分子间缔合，沸点升高，熔点升高-可形成分子间或分子内氢键Inter- & intra-molecular hydrogen bond A water molecule can form up to four hydrogen bonds.Hydrogen bonding by a water molecule around a molecule in the solid in the liquidStructure and Prope
8、rties of WaterBecause of Hydrogen Bonding.lWater has a uniquely high specific heat (1 cal/gC) and a uniquely high heat of vaporization (541.6 cal/g). Thermal regulation of the climate. Absorbs heat during the day (vaporization of water) Warms the earth during the night (dew etc.).lThe density of sol
9、id water is less than liquid water. Very unusual. This allows life to exist in our oceans and lakes.DNA分子中存在氢键Ion-Dipole Forces- Interaction between an ion (Na+) and a dipole (water).- Strongest of all intermolecular forcesHydrophobic Interactions-The tendency of nonpolar molecules to self-associate
10、 in water defined as hydrophobic effect. StraightflushJunkJohnshandDaveshand1878年，L.Boltzman提出了熵与微观状态数的关系S =k lnW W:thenumberofpossiblearrangementsinthesystem k:Boltzmanns constant-The driving force is increased solvent entropy. Weak Interactions Are Crucial to Macromolecular Structure and Function
11、InteractionExampleEnergy离子键Na+ Cl- 400 -4000 kJ/mol共价键 H - H 150-1100 kJ/molion-dipole (I-D) Na+ H2O 40-600 kJ/moldipole - dipole (D-D) HCl HCl 5-25 kJ/moldipole - induce dipole (D-ID) HCl O2 2-10 kJ/molLondon Dispersion (LD) N2 N2 0.05 - 40 kJ/mol H-Bond(10-40)kJ/molH-Bond(10-40)kJ/mol-Relative str
12、ength Strongly repulsive at short internuclear distances, very weak at long internuclear distances-Working Range-Very important in protein folding results in a great variety of protein shapes & sizes Properties of SolutionsColligative Properties1. lowering the Vapor Pressure2. Boiling-Point Elevatio
13、n3. Freezing-Point Depression4. Osmosis Factors Affecting SolubilityDynamic equilibriumFactors Affecting Solubility-The solution processSolvationHydration1. Solute-solute interactions2. Solvent-solvent interactions2. Solute-solvent interactions-Solution FormationEnergy ChangesSpontaneity and Disorde
14、r. Processes in which the energy content of the system deceases tend to occur spontaneously. Processes in which the disorder of the system increases tend to occur spontaneously.NH4NO3H=26.4kJ/mol.Substances with similar intermolecular attractive forces tend to be soluble in one another.-“Like dissol
15、ves like”-CH2-CH2-C-OHO-CH-CH3CH3Colligative Properties. Differ from those of the pure solvent. Depend primarily on the concentration not the kind of solute particles“Depending on the collection”-The vapor pressure of a liquid is the pressure exerted by its vapor when the liquid and vapor states are
16、 in dynamic equilibrium.- A nonvolatile solute reduces the rate of vaporization of the solvent.- The extent to which a nonvolatile solute lowers the vapor pressure is proportional to its concentration.-Boiling point-Liquids boil when the external pressure equals the vapor pressure.-Two ways to get a liquid to boil: increase temperature or decrease pressure.-Normal boiling point is the boiling point at 760 mmHg (1 atm).- Boiling point is dependent on the intermolecular forcesPolar molecules have
