5-分子间和分子内的相互作用力

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1、(Intermolecular Forces)之物质结构（之物质结构（3）分子间作用力分子间作用力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 Fun

2、ction Intermolecular ForcesStates of MatterKinetic energies of the particle Intermolecular ForcesTemperatureInstantaneous dipolePermanent dipoleThe Origination of Intermolecular Forces Types of Intermolecular ForcesOrientation ForceInduction ForceLondon Dispersion ForceH-BondingIon-Dipole ForcesHydr

3、ophobic InteractionsOrientation ForceDipole Dipole ForcePolar moleculePolar moleculeInduction ForceDipole Induced Dipole ForcePolar moleculePolar moleculePolar moleculeNonpolar moleculeLondon Dispersion ForceInduced Dipole Induced Dipole ForcePolar moleculePolar moleculePolar moleculeNonpolar molecu

4、leNonpolar moleculeNonpolar moleculePolarizabilityDispersion force tends to increase with increasing molecular massSummaryOrientation ForceInduction ForceDispersionForcePolar moleculePolar moleculePolar moleculeNonpolar moleculeNonpolar moleculeNonpolar moleculevan der Waals Forces分子偶极矩（实）/10-30Cm取向

5、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B.P.increase with the M.W.increasingExcept for van der Waals forces,there must be some other force氢键氢键(H-Bonding)NOFFNO极性共价键极性共价键an unshared electron pair

6、One 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 hydrogen atom bonded to another O,N,or F.high boiling pointslow boiling points分子间缔合，沸点升高，熔点升高分子间缔合，沸点升高，熔点升高-可形成分子间或分子内氢

7、键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 Properties of WaterBecause of Hydrogen Bonding.lWater has a uniquely high specific heat(1 cal/gC)and a

8、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 solid water is less than liquid water.Very unusual.This allows life to exist in our oceans and lakes.DNA 分子中存

9、在氢键分子中存在氢键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 in water defined as hydrophobic effect.Straight flushJunkJohns handDaves hand1878年，年，L.Boltzman提出了熵与微观状态

10、数的关系提出了熵与微观状态数的关系S=k lnW W:the number of possible arrangements in the system k:Boltzmanns constant-The driving force is increased solvent entropy.Weak Interactions Are Crucial to Macromolecular Structure and Function Interaction ExampleEnergy离子键离子键Na+Cl-400-4000 kJ/mol共价键共价键 H-H 150-1100 kJ/molion-d

11、ipole(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-Relative strength Strongly repulsive at short internuclear distances,very weak at long internuclear distances-Working Range-Very important in prote

12、in folding results in a great variety of protein shapes&sizes Properties of SolutionsColligative Properties1.lowering the Vapor Pressure2.Boiling-Point Elevation3.Freezing-Point Depression4.Osmosis Factors Affecting SolubilityDynamic equilibriumFactors Affecting Solubility-The solution processSolvat

13、ionHydration1.Solute-solute interactions2.Solvent-solvent interactions2.Solute-solvent interactions-Solution FormationEnergy ChangesSpontaneity and Disorder.Processes in which the energy content of the system deceases tend to occur spontaneously.Processes in which the disorder of the system increase

14、s tend to occur spontaneously.NH4NO3H=26.4kJ/molCCHHHHHHOHOCCHHHHHCCHHHHHHOHOH(a)乙醇分子间形成氢键(b)乙醇分子与水分子之间形成氢键.Substances with similar intermolecular attractive forces tend to be soluble in one another.-“Like dissolves like”-CH2-CH2-C-OHO-CH-CH3CH3Colligative Properties.Differ from those of the pure so

15、lvent.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 in dynamic equilibrium.-A nonvolatile solute reduces the rate of vaporization of the solv

16、ent.-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 boili

17、ng point at 760 mmHg(1 atm).-Boiling point is dependent on the intermolecular forcesPolar molecules have higher b.p.than nonpolar molecules-Freezing point The freezing point corresponds to the temperature at which the vapor pressures of the solid and liquid phases are the same.The Concentration of S

18、olute Particles#Nonelectrolytes：One mole of a nonelectrolyte produces one mole of solute particles csolute particles=c#Electrolytes:Exist as ions in solution Provide more than one mole of particles per mole of solute dissolved cs.p.=ic,i is the moles of solute particles per mole solute1.Lowering the

19、 Vapor PressureDissolved solute lowers vapor pressure of solvent.PA=A PARoaults LawPA:the vapor pressure of the solutionXA:the mole fraction of the solventPA:the vapor pressure of the pure solventIdeal solutions:Real solutions:When the solute concentration is low and when the solute and the solvent

20、are much alike in molecular size and in the strength and type of intermolecular attractions.What you expect for the vapor pressure when the intermolecular forces between solvent and solute are weaker than those between solvent and solvent and between solute and solute.Conversly,what you expect when

21、the interactions between solute and solvent are exceptionally strong?2.Boiling-Point Elevation And3.Freezing-Point Depression Tb=Kb m Tf=Kf mKb:molal boiling-point elevation constantm-molality:the number of moles of solute per 1000 g of solventKf:molal freezing-point depression constant强电解质的依数性偏差强电解

22、质的依数性偏差(Deviation of Colligative Properties for Strong Electrolytes)电解质稀溶液的依数性电解质稀溶液的依数性:p=iKbB Tb=iKbbB Tf=iKf bB难挥发的非电解质稀溶液的依数性难挥发的非电解质稀溶液的依数性:p=KbB Tb=KbbB Tf=Kf bB 对对AB型强电解质（型强电解质（NaCl）,i2 A2B型（型（Na2SO4）或）或AB2型（型（MgCl2）强电解质，强电解质，i3(近似值近似值).i 称校正因子称校正因子Molarity(M)=Amount of solute(in moles)Volume

23、 of solution(in liters)Molality(m)=Amount of solute(in moles)Mass of solvent(in kilograms)An antifreeze solution is prepared containing 40.0 g of ethylene glycol(molar mass=62.0 g/mol)in 60.0 g waterCalculate the freezing and boiling points of this solution.Solution:KgmolbB/8.10100.6010.620.403For w

24、ater,Kf=1.86 and Kb=0.52 CTf1.208.1086.1CTb6.58.1052.0Hence the solution should freeze at 20.1 and boil at 105.6.4.OsmosisDiffusionMicrocon Centrifugal Filter Unit超滤膜(ultra-filtration membrane)透析袋(dialysis tubing)产生渗透条件产生渗透条件:渗透方向渗透方向：稀溶液稀溶液 浓溶液浓溶液渗透现象会无止境地进行下去吗渗透现象会无止境地进行下去吗?The net movement of sol

25、vent is always toward the more concentrated solution.渗透现象渗透现象半透膜半透膜产生渗透原因产生渗透原因-Osmosis PressureThe Pressure required to prevent osmosis.PV=nRT P=cRTExample:Calculate the osmotic pressure of 0.10 mol/Lglucose solution at 25.How about 0.10 mol/L NaCl solution?Solution:cos(glucose)=cglucose=0.10 mol/L

26、 P(glucose)=cosRT=0.10 x8.31x298=250 kPacos(NaCl)=i c=2x0.10=0.20 mol/L P(NaCl)=0.20 x8.31x298=500 kPaThe unit here is kPa!Jacobus Henricus vant Hoff1852-1911 例：例：25时，求时，求0.9%的生理盐水的渗透压是多少？的生理盐水的渗透压是多少？kPa)(763298314.8154.02icRT)Lmol(154.05.581000%9.01-NaClc-1NaClmolg5.58M渗透浓度渗透浓度(Osmolarity)单位:渗透摩尔每

27、升（Osmol/L）或毫渗透摩尔每升（mOsmol)每升溶液中所能产生渗透效应的各物质质点的总浓度正常人血浆总渗透浓度为正常人血浆总渗透浓度为 303.7-1Losmol m等渗溶液等渗溶液:280-320 mOsmol/L低渗溶液低渗溶液:320 mOsmol/L 临床规定临床规定渗透方向：低渗渗透方向：低渗 高渗高渗-Osmosis and living cellIsotonicHypertonicHypotonic例例:1.00 g of heme is dissolved in water and diluted to 100 mL.At 20,the osmotic pressure

28、 is measured to be0.366 kPa.Calculate the molar mass of heme.How about the freezing point of the solution?Solution:P=cRT;c=P/(RT)=0.366/(8.81x293)=1.50 x10-4 mol/Ln=cV=1.50 x10-4x100 x10-3=1.50 x10-5 molMolar mass=m/n=1.00/1.50 x10-5=6.67x104 g/molTf=KfbB=Kfc=1.50 x10-4x1.86=2.79x10-4Hence this heme

29、 solution should freeze at 0.00 例例:1.00 g of heme is dissolved in water and diluted to 100 mL.At 20,the osmotic pressure is measured to be0.366 kPa.Calculate the molar mass of heme.How about the freezing point of the solution?(Kf=1.86)Important termsIntermolecular forcesVan der Waals forcesDipole-di

30、pole forcesLondon(dispersion)forcesHydrogen bondingColligative propertiesVapor-pressure-loweringBoiling-point elevationFreezing-point depressionOsmosisOsmotic pressureReviewAtom MoleculeSubstancesIMFOrientation ForceInduction ForceLondon Dispersion ForceH-BondingIon-Dipole ForcesHydrophobic Interact

31、ionsSolubilityColligative propertiesIncreased EntropyMolecular polarizationSummary of concepts6渗透压渗透压半透膜半透膜等渗等渗低渗低渗高渗高渗Vant Hoff 定律：定律：=c RT;=i c RT浓度差浓度差稀溶液的稀溶液的依数性依数性溶液与溶剂之间或浓溶液与稀溶液之间溶液与溶剂之间或浓溶液与稀溶液之间渗渗透透方方向向沸点升高沸点升高/冰点下降冰点下降Tb=Kb mTf=KfmSummary of conceptsSkills1.Identifying intermolecular forces2.Determining the boiling points on the basis of intermolecular forces3.Calculating osmotic pressure,boiling-point elevation and freezing-point depression.Questions 习题P193:4,6,8,12,14P168:7,8,10,15THE END