One of the common sub-instances of these entities is stabilized by hyperconjugative donation from a sigma-C-H orbital into the substituent antibonding orbital, its namesake "effect," and is named for the presence of substituents with bond angles between 30 and 90 degrees; another has substituents atop one another in the relevant Newman projection and, while generally unstable, can cause disequilibrium among its stable relatives if its activation energy is too high.
One of the common sub-instances of these entities is stabilized by hyperconjugative donation from a sigma-C-H orbital into the substituent antibonding orbital, its namesake "effect," and is named for the presence of substituents with bond angles between 30 and 90 degrees; another has substituents atop one another in the relevant Newman projection and, while generally unstable, can cause disequilibrium among its stable relatives if its activation energy is too high. Cases in which this type of isomer can occur are limited by the fact that pi bonds disallow longitudunal twists in general, so it requires the presence of formal sigma bonds. The aforementioned instances of these are the gauche and eclipsed ones. The simplest class of these is defined by orientation about a single sigma bond and is the rotamers. For 10 points, name this category of stereoisomers that are interconverted between by rotations about single bonds.
One of the common sub-instances of these entities is stabilized by hyperconjugative donation from a sigma-C-H orbital into the substituent antibonding orbital, its namesake "effect," and is named for the presence of substituents with bond angles between 30 and 90 degrees; another has substituents atop one another in the relevant Newman projection and, while generally unstable, can cause disequilibrium among its stable relatives if its activation energy is too high.
{conformational isomers} [or {conformers}; accept {rotamers} until it's mentioned and prompt on it afterwards]