Eclipsed/staggered

Figure 3a,b,c. Sixfold and threefold rotors X and Y are halogens in this work. For the sixfold case, we define a = 0° with one CH bond in the plane of the ring (eclipsed). Staggered geometry (a = 90°) then has one CH bond perpendicular to the plane of the ring. For the threefold case shown in the center, we define a = 0° with one CH bond "pseudo-trans" to the substituents X and Y. 

Alkane conformations can be classified as eclipsed, staggered, anti, or gauche depending on the relative orientation of the groups on adjacent carbons. 

The mathematical way of describing conformation is by the calculation of the torsion angles about each bond the input data are the atomic coordinates. A torsion is the extent of the twist of substituents about a bond. It is a way of looking along a bond and describing the disposition of the substituents attached to the atoms at both ends. It will indicate if the bonds to the substituent groups are eclipsed, staggered, or intermediate between these. 

Eclipsed, staggered, gauche cis and trims conformations as applied to, for example, propane and butane... 

Problem 4.13. Draw Newman and sawhorse projections of 2-methylbutane. Identify eclipsed, staggered, gauche, and antirelationships between sets of methyl groups looking down the C2-C3 bond in your representation of the structure. 

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