MCAT Organic Chemistry: Isomers and Conformational Analysis

Comprehensive vocabulary flashcards covering structural isomers, stereoisomers, Newman projections, butane confirmational analysis, and cyclohexane chair conformations from Chapter 2 of the MCAT Organic Chemistry series.

Structural Isomers

Compounds that share the same molecular formula but differ in how their atoms are connected, leading to differences in physical and chemical properties; also known as constitutional isomers.

Stereoisomers

Isomers that share both the same molecular formula and the same connectivity of atoms, but differ in the spatial arrangement of those atoms.

Confirmational Isomers

Stereoisomers that arise from differences in rotation around single ($\sigma$) bonds and can interconvert without breaking and reforming chemical bonds.

Configurational Isomers

Stereoisomers that cannot interconvert without breaking and reforming chemical bonds.

Enantiomers

Chiral configurational stereoisomers that are non-superimposable mirror images of each other.

Diastereomers

Configurational stereoisomers that differ in spatial arrangement without being related as mirror images.

Cis/Trans Isomers

A subtype of diastereomers, also known as geometric isomers, that differ in substituent arrangement around an immovable bond (such as a double bond or a ring structure), where groups are on the same side (cis) or opposite sides (trans).

Newman Projection

A visualization method that looks directly down the axis of a carbon-carbon bond, depicting the front carbon as a dot and the back carbon as a circle around it.

Dihedral Angle

The angle formed between two planes, specifically the angle between bonds on the front and back carbons in a Newman projection.

Torsional Strain

Strain arising from repulsive interactions between electron clouds in adjacent or overlapping bonds.

Anti-Conformation

A staggered conformation where the two largest groups are positioned opposite each other with a dihedral angle of $180^\circ$, minimizing steric and torsional strain to yield the lowest energy, most stable state.

Gauche Conformation

A staggered conformation where the two largest groups are positioned adjacent to one another with a dihedral angle of $60^\circ$, introducing steric strain that makes it less stable than the anti-conformation.

Eclipsed Conformation

A conformation where substituents on the front and back carbons align and overlap with a dihedral angle of $120^\circ$, creating torsional strain due to electron repulsion.

Totally Eclipsed Conformation

A conformation where the two largest groups directly overlap with a dihedral angle of $0^\circ$, maximizing both steric and torsional strain to produce the highest energy, least stable state.

Ring Strain

The overall destabilizing strain experienced by cyclic molecules, which arises from angle strain, torsional strain, and nonbonded (steric) strain.

Angle Strain

The strain introduced into a cyclic molecule when bond angles deviate from their ideal values due to being compressed or stretched.

Nonbonded Strain

Destabilizing strain (also called steric strain) resulting from non-adjacent atoms or groups crowding into the same physical space.

Chair Conformation

The most stable conformation of cyclohexane that minimizes angle strain by maintaining nearly ideal bond angles and minimizes torsional strain by staggering bonds.

Axial Position

Substituent positions on a cyclohexane chair conformation that point vertically up or down, alternating orientation at each successive carbon around the ring.

Equatorial Position

Substituent positions on a cyclohexane chair conformation that point outward roughly along the plane of the ring, alternating slightly up or down in opposition to the axial position on the same carbon.

1,3-Diaxial Interactions

Destabilizing steric clashes that occur between a bulky substituent positioned axially on a cyclohexane chair and other axial hydrogens on the same side of the ring.

Ring Flip

The dynamic inversion of a cyclohexane chair conformation in which all axial substituents become equatorial and all equatorial substituents become axial.