Solved Problem 1 Predicting the Direction of a Dipole Moment Make a three-dimensional drawing of methylamine, CHaNH2,and show the direction of its dipole moment (1.31) Strategy Look for any lone-pair electrons Identify any atom with an electronegativity substantially different from that of carbon (usually O,N,F,Cl,or Br) Electron density will be displaced in the general direction of the electronegative atoms and the lone pairs
Make a three-dimensional drawing of methylamine, CH3NH2, and show the direction of its dipole moment (µ = 1.31) Solved Problem 1 Predicting the Direction of a Dipole Moment Strategy Look for any lone-pair electrons Identify any atom with an electronegativity substantially different from that of carbon (usually O, N, F, Cl, or Br) Electron density will be displaced in the general direction of the electronegative atoms and the lone pairs
Solved Problem 1 Predicting the Direction of a Dipole Moment Solution H Methylamine has an H electronegative nitrogen atom and a lone pair of electrons. The dipole moment thus points generally from-CHa toward the nitrogen H Methylamine (w=1.31)
Solution Methylamine has an electronegative nitrogen atom and a lone pair of electrons. The dipole moment thus points generally from –CH3 toward the nitrogen Solved Problem 1 Predicting the Direction of a Dipole Moment
Sec 2 Formal Charges Formal charge The difference in the number of electrons owned by an atom in a molecule and by the same atom in its elemental state Formal charges do not imply the presence of actual ionic charges Device for electron“bookkeeping'” Formal negative Formal positive Assigned to specific atoms within a charge on oxygen charge on sulfur Dimethyl sulfoxide CHgSOCH :0: H Dimethyl sulfoxide Sulfur atom has three bonds rather than the usual two and has a formal positive charge Oxygen atom has one bond rather than the usual two and has a formal negative charge
Sec 2 Formal Charges Formal charge The difference in the number of electrons owned by an atom in a molecule and by the same atom in its elemental state Formal charges do not imply the presence of actual ionic charges Device for electron “bookkeeping” Assigned to specific atoms within a molecule Dimethyl sulfoxide CH3SOCH3 Sulfur atom has three bonds rather than the usual two and has a formal positive charge Oxygen atom has one bond rather than the usual two and has a formal negative charge
Sec 2 Formal Charges Formal Charge Determination An isolated carbon atom This carbon atom also owns owns 4 valence electrons. H =4valence electrons. 2 H: C:H H An isolated nitrogen atom This nitrogen atom also owns owns 5 valence electrons. +5valence electrons. 6 N H:N:H H LeaingAllRigh Rservd
Sec 2 Formal Charges Formal Charge Determination
Sec 2 Formal Charges Number of Number of Formal charge = valence electrons valence electrons in free atom in bonded atom Number of Number of Number of valence electrons bonding electrons nonbonding in free atom 3 electrons For sulfur: Sulfur valence electrons =6 Sulfur bonding electrons =6 Sulfur nonbonding electrons =2 :O: Formal charge =6-6/2-2 =+1 H、 For oxygen: H Oxygen valence electrons =6 Oxygen bonding electrons =2 Oxygen nonbonding electrons 6 Formal charge=6-2/2-6 =-1
Sec 2 Formal Charges