1. CH 4-3: An Introduction to Alkane Conformations
Conformations are different 3-Dimensional (3-D) orientations of a molecule due to rotations about C-C single (sigma) bonds.
Conformations of butane (C2H6):

2. Conformations of butane:

3. C-C Bond Rotations: Review of Terminology
Staggered Conformation: stable conformation where all the substituent groups are “staggered” or spaced as far apart as possible.
Anti-Conformation: largest substituent groups are as far apart as possible (180o) – most stable conformation
Eclipsed-Conformation: less stable conformation where groups “eclipse” each other.
Syn-Eclisped: largest substituent groups are eclipsed - least stable conformation
Newman Projection: 2-Dimensional (2-D) way to represent 3-Dimensional (3-D) conformational changes due to rotation at a specific C-C bond. See video CH 4-4.