Part 5: Rotation around C-C bonds

Learning Goals: Learn how relatively free rotation around single bonds in linear and branched alkanes (and other organic compounds) generates many conformations.  Understand the meaning of dihedral angle and how it is measured, and the reasons why energy changes with dihedral angles around single (and double) bonds.   Know that rotational barriers less than 10 kcal/mol (single, triple bonds) result in a range of conformations, while rotational barriers greater than 30 kcal/mol (double bonds) result in geometric isomerism (cis/trans).

Reading: Soderberg section on open-chain organic molecules.

Notes: A two-page old pencast* describes conformations in alkanes, including definitions of dihedral angles. A single page pencast* compares the energy effects of rotation about single, double and triple bonds and describes why only double bonds result in geometric isomerism.  The end of this pencast* describe the C-N bonds in amides, which behave as if they have partial double bond character.  Finally, there is a brief pencast* on alkene nomenclature. (*-Audio from old pencasts does not work.  Ignore the warning about needing to update to latest Adobe Reader - see note in first topic).