Organic Chemistry: Dimensions and Dipoles

Shapes of molecules are super important in organic chemistry. like everything else…

We use the VSPER theory to discuss the shape of molecules. The VSPER theory, pronounced vesper, takes into account how valence electrons interact with each other.

  • Lewis structure drawn
  • count number of bonds
  • count number of lone pairs  (non-bonding electrons)

lone pair/lonepair >bondpair/lone pair>bonded pair/bonded pair

lone pairs lie closer to the central atom and hence repel more than the bonded pair. Above is the order of repulsion.

Name of Shape Spatial Arrangement Number of bonds/lone pairs
linear 180 2
trigonal planar 120 3
tetrahedral 109.5 4
trigonal bipyrimdal 120, 90 5
octahedral 90 6

For the purposes of my class, we are mainly concerned with molecules with bonds up to tetrahedral spatial arrangement. After all, that is Carbon’s go to arrangement with its four valance electrons.

But Nicole, how does this effect the properties of the molecule? According to the electronegativity and size of the molecule there could be:

  • Dipole moment
  • London forces and van der Waals forces
  • Hydrogen bonding

In organic chemistry we are also concerned about the degree to which a molecule is unsaturated.

Degrees of Unsaturation (DU)=

Table of charge-charge interaction

Type of Charge Polarity Strength

formal charge = valence electrons – unshared electrons -1/2 (no. of shared electrons)

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