rganic hemistry Review Information for Unit 1 VSEPR ybrid rbitals Polar Molecules
VSEPR The valence shell electron pair repulsion model (VSEPR) can be used to predict the geometry around a particular atom in an organic compound. VSEPR assumes that the electron domains around a particular atom will be arranged in a way that minimizes repulsion between the negatively charged regions containing electrons.
VSEPR Electron domain: a region in space (around a particular atom) that contains electrons Electron domain geometry: the arrangement of electron domains around a particular atom 2 electron domains linear 3 electron domains trigonal planar 4 electron domains tetrahedral Remember: Double and triple bonds count as one electron domain.
VSEPR You must be able to determine the electron domain geometry around a specified atom in an organic compound. Draw the Lewis structure ount the number of electron domains Assign the electron domain geometry
VSEPR Example: What is the electron domain geometry around in the following molecule? Around N? N
VSEPR Example: What is the electron domain geometry around in the following molecule? Around N? N Answer: : 4 electron domains tetrahedral N: 4 electron domains tetrahedral
VSEPR Example: Identify the electron domain geometry for,, and N for the following compound. N 2 N
VSEPR Example: Identify the electron domain geometry for,, and N for the following compound. N Answer: N 2 N Trigonal planar N 2 tetrahedral
ybrid rbitals Simple overlap of atomic orbitals containing unpaired electrons generally does not adequately explain the geometries of organic compounds. Valence bond theory uses hybrid orbitals to explain and predict structures and geometries of organic compounds atomic orbitals formed when two or more orbitals on the same atom are mixed
ybrid rbitals Atomic rbitals ombined ybrid rbitals Produced s, p two sp hybrid orbitals s, p, p three sp 2 hybrid orbitals s, p, p, p four sp 3 hybrid orbitals s, p, p, p, d five sp 3 d hybrid orbitals s, p, p, p, d, d six sp 3 d 2 hybrid orbitals Note: nly sp, sp 2, and sp 3 hybrid orbitals are important in organic compounds.
ybrid rbitals Each type of hybrid orbital is associated with a particular type of electron domain geometry. the same geometry that would be predicted by VSEPR ybrid # of Electron Electron Domain rbital Set Domains Geometry sp 2 linear sp 2 3 trigonal planar sp 3 4 tetrahedral sp 3 d 5 trigonal bipyramidal sp 3 d 2 6 octahedral
ybrid rbitals Example: Identify the hybrid orbitals used by each in the following compound. 2 2 Step 1: Draw the Lewis structure:
ybrid rbitals Step 2: ount the number of electron domains around each carbon and use that to identify the hybrid orbitals: 2 2 4 3 Answer: sp sp sp 3 sp 2
Polarity The polarity of a bond is measured by its dipole moment. The polarity of a molecule is measured by its molecular dipole moment. Dipole moment of a molecule as a whole indicator of a molecule s overall polarity vector sum of individual bond dipole moments reflects magnitude and direction of individual bond dipole moments
Polarity ompare formaldehyde and 2 : Formaldehyde has 1 polar = bond molecular dipole moment = 2.3 2 has 2 polar = bonds molecular dipole moment = 0 WY??
Polarity In some molecules like 2, the bond dipole moments cancel out due to the molecule s electron domain geometry. m = 2.3 D m = 0
Polarity In order to determine if a molecule is polar or not, you must: draw a 3-D structure for the compound Use VSEPR to determine the electron domain geometries around each atom identify the direction of the dipole moments for each polar bond determine if the vector sum of the individual dipole moments leads to a nonzero molecular dipole moment (i.e. a polar molecule)
Polarity 3 Example: Determine if each of the following compounds is polar or nonpolar. For those that are polar, determine the direction of the molecular dipole moment. 3 3 l 4 3 3 3
Polarity Draw Lewis structures and draw 3-D structure showing geometry of polar bonds in the molecule: 3 3 l l l l 3 3
Polarity Show dipole moments for each polar bond: 3 3 l l l l 3 3
Polarity Determine if molecule has a dipole moment. l l l Dipole moments cancel out. nonpolar l 3 3 polar Molecular dipole moment