Conformations Stereoisomers around single bonds

The staggered and eclipsed forms of ethane are conformational stereoisomers (conformational isomers, conformers) because they have the same molecular formulas and sequences of bonded elements but different spatial arrangements due to rotations around single bonds. (Actually there are an infinite number of conformational isomers (also called conformations) because there are an infinite number of degrees of rotation around the bond, but normally one only needs to be concerned with energy minima and maxima.)... 

Conformation In a molecule of a given constitution and configuration, the spatial array of atoms affording distinction between stereoisomers that can be interconverted by rotation around single bonds. The chirality sense of conformations may be specified using the P, M nomenclature. 

We will now discuss at some length the many ways in which deviations from standard bonding parameters lead to energetic destabilization of a molecule. We will focus on "stable" structures (i.e., not on reactive intermediates), but the notions we develop here also apply to reactive intermediates. We first explore acyclic systems, wherein molecular motions directly lead to strained forms. Note that we are not yet considering conventional chemical reactivity. We will be considering conformers, or conformational isomers. Recall that conformers are stereoisomers that interconvert by rotation around single bonds (see Chapter 6 for definitions of stereochemical concepts). These isomers are not to be confused with constitutional isomers, where the molecular formula is the same, but the atoms are arranged differently. 

If compounds have the same topology (constitution) but different topography (geometry), they are called stereoisomers. The configuration expresses the different positions of atoms around stereocenters, stereoaxes, and stereoplanes in 3D space, e.g., chiral structures (enantiomers, diastereomers, atropisomers, helicenes, etc.), or cisftrans (Z/E) configuration. If it is possible to interconvert stereoisomers by a rotation around a C-C single bond, they are called conformers. 

Collapse of 48 through formation of the second C-C bond would give 45 and an overall stereospecific addition. However, rotation around the C-C single bond of 48 forms a different radical conformation, 49, which would collapse to the other stereoisomer, 46 ... 

Atropisomers Stereoisomers arising from restricted rotation around a single bond (i.e., conformers), with a high enough rotational barrier that the isomers can be isolated (16 - 20 kcal/mole at room temperature), such as ortho-... 

The arrangement of bonds around a chiral carbon atom or a double bond is called configuration. When two structures differ by rotation around one or more single bonds, they are called conformers or rotamers, and usually they are more easily interconvertible than stereoisomers rotamers can, however, be stable compounds when considerable steric hindrance is present." In ethane viewed straight-on with superimposed carbon atoms, when the configurations of the two carbon atoms overlap, the confor-... 

Different conformations (shapes) of the same molecule that are interconvertible by rotation around a single bond are called conformers or rotamers. Conformers are stereoisomers, isomers with the same atom connectivity but different spatial arrangements of atoms. 

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