Electronegativity Polar Covalent Bonds Potential Maps Functional by qiy16524

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									            Electronegativity
          Polar Covalent Bonds
             Potential Maps
           Functional Groups
              Boiling Points




    Neighbor Distorts Electrons
    all 0.002 isodensity surfaces, but not same size/shape near H




more electron                                  less electron
density near H                                density near H




                                                                    1
                 Electronegativity
 • The ability of an atom to attract electron
   density (electrons) to itself

             Li < Be < B < H < C < N < O < F
                      I < Br < Cl < F
            Low                          High




            Bond Polarity Spectrum


                        covalent
  very polar              polar        nonpolar
ΔEN large                                       ΔEN zero


      ionic                             covalent




                                                           2
          Electrostatic Potential

probe
 at ∞
                     probe
                    at (x,y,z)           polar molecule
                                        creates electrical
                                              field



               Potential at (x,y,z) =
            ΔE(probe infinity    (x,y,z))




        From Potential to Charge

        potential < 0            potential > 0




 • sign tells which charge dominates
 • magnitude tells how large the charge is




                                                             3
        Spartan Potential Maps

 • Painted SIZE density surface

 • color scale


      most        ½ way            most
     negative                     positive




          Potential Map of H2O

SIZE density
  surface




                                             4
          Potential Map of H2O

most negative
  potential




                  most positive potential




                Color Scales
• Default          red = lowest, blue = highest
      • Good for comparisons inside molecule
      • Makes all molecules seem polar


• Standard         red = -40, blue = +40 kcal/mol
      • Small potentials = yellow, green, light blue
      • Good for locating important sites
      • Hides extreme behavior red ≤ -40, blue ≥ +40




                                                       5
                               CH3Cl




     Colors: -20   25                   -40   +40
              Default                    Standard




               CH3Cl & (CH3)2CHCl




Seen one chloroalkane, seen ‘em all …




                                                    6
                    Aldehyde & Ketone


acetaldehyde                                                         acetone




      Neg potential/charge concentrated on O, Pos potential/charge diffuse




                     Ether & Alcohol



   dimethyl ether                                               ethanol




                                                     actual range = -42      +51




                                                                                   7
         Alcohol & Carboxylic Acid



  acetic acid                                            ethanol




                                               actual range = -42     +51
actual range = -38      +56




   Carboxylic Acid, Ester, Amide
                                    ethyl acetate

                                                                -50
   -38

          +56



                                                                      +53
                              -42




                acetic acid                         acetamide




                                                                            8
Ethylamine & Trimethylamine



                   -50                    -40




       Amine, Amide, Nitrile



             -50                          -44




                                     -9




ethylamine               acetamide              acetonitrile




                                                               9
 groups containing negative atoms
• Not
  – Cl (-20), amide C(=O)N (-9), “alkyl” C(=O)OH (-22)
• Carbonyl O
  – RCH=O (-39), RC(=O)R’ (-42)
  – C(=O)OH (-38), C(=O)OR (-42), C(=O)NH2 (-50)
• Alkyl O
  – ROH (-42), ROR’ (-38)
• “Localized” N
  – amine R3N (-50), nitrile RC≡N (-44)




 groups containing positive atoms
• Not
  – C or CH
• Hydroxyl OH
  – ROH (+51), C(=O)OH (+56)
• Amine & amide NH
  – RNH2 (+30), C(=O)NH2 (+53)




                                                         10
        extremely polar groups
•   Alcohol                ROH                  -42   +51
•   Carboxylic acid        RC(=O)OH             -38   +56
•   Amide                  RC(=O)NH2            -50   +53
•   Amine?                 RNH2                 -50   +30




           Noncovalent Forces
• Electrostatic
    – Strength correlated with charge
    – Many types of charges
       • Ion, dipole (H-bond), induced dipole


• van der Waals (vdW)
    – instantaneous dipole-instantaneous dipole
    – repulsive at short distances (Pauli)




                                                            11
            NaCl (Ion-Ion)




               standard scale




  Not All Dipole-Dipole Equal
• CH3CH2OH         liquid




• CH3OCH3          gas



               Standard scale




                                12
                  Boiling Point Trends
       200


       150


       100
                                                       RCH3
                                                       RNH2
 bp     50                                             ROH
(oC)                                                   RF
                                                       RSH
         0
              1    2    3     4    5    6    7     8

        -50
                                   #C in R

       -100




              Hydrophobic Alcohols



 HO
                            cholesterol (mp 148)


                                   α-tocopherol (Vitamin E)
                   HO


                              O




                                                              13

								
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