ch._1_2,_polar_covalent_bonds_acids_and_bases

ch._1_2,_polar_covalent_bonds_acids_and_bases - Organic...

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Organic Chemistry M. R. Naimi-Jamal Faculty of Chemistry Iran University of Science & Technology
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Polar Covalent Bonds Acids and Bases Chapter 1. Continue Based on: McMurry’s  Fundamental of Organic Chemistry , 4th  edition, Chapter 1
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3 Polar Covalent Bonds: Electronegativity Covalent bonds can have ionic character These are  polar covalent bonds Bonding electrons attracted more strongly by  one atom than by the other  Electron distribution between atoms in not  symmetrical
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4 Bond Polarity and Electronegativity Electronegativity  (EN):  intrinsic  ability  of  an  atom to attract the shared electrons in a covalent  bond Differences in EN produce bond polarity Arbitrary  scale.  As  shown  in  next  figure,  electronegativities  are  based  on  an  arbitrary  scale F is most electronegative (EN = 4.0), Cs is least  (EN = 0.7)
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5 The Periodic Table and Electronegativity
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6 Bond Polarity and Electronegativity Metals on left side of periodic table attract  electrons weakly:  lower  electronegativities Halogens and other reactive nonmetals on right  side of periodic table attract electrons strongly:  higher  electronegativities Electronegativity of  C = 2.5 
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7 Bond Polarity and Inductive Effect Nonpolar Covalent Bonds : atoms with similar  electronegativities Polar Covalent Bonds:  Difference in EN of atoms < 2 Ionic Bonds:  Difference in electronegativities > 2  (approximately). Other factors (solvation, lattice energy, etc) are  important in ionic character.
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8 Bond Polarity and Inductive Effect Bonding  electrons  are  pulled  toward  the  more  electronegative atom in the bond Electropositive  atom  acquires  partial  positive  charge,  δ + Electronegative  atom  acquires  partial  negative charge,  δ - Inductive effect: shifting of electrons in a bond in  response  to  the  electronegativities  of  nearby  atoms 
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9 Electrostatic Potential Maps Electrostatic potential maps show calculated charge  distributions Colors indicate electron-rich (red) and electron-poor  (blue) regions
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10 Polar Covalent Bonds: Dipole Moments Molecules as a whole are often polar, from vector  summation of individual bond polarities and lone- pair contributions
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11 Polar Covalent Bonds: Dipole Moments Dipole moment - Net molecular polarity, due to  difference in summed charges   μ   - magnitude of charge Q at end of molecular  dipole times distance r between charges   μ  = Q  ×  r, in debyes (D) 1 D = 3.34  ×  10 - 30  coulomb meter
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12 Dipole Moments in Water and Ammonia Large dipole moments Electronegativities of  O and N > H Both O and N have lone-pair electrons oriented  away from all nuclei
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This note was uploaded on 12/21/2011 for the course HORT 121 taught by Professor Mcmurry during the Spring '11 term at American College of Gastroenterology.

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ch._1_2,_polar_covalent_bonds_acids_and_bases - Organic...

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