Kaplan Organic Chemistry: Chapter 2 - Isomers

DEF:Isomers

Compounds with the same molecular formula but different structures.

DEF:Structural Isomers

Isomers that share the same molecular formula but differ in connectivity of atoms.

DEF:Stereoisomers

Isomers with the same molecular formula and connectivity but differ in spatial arrangement.

DEF:Conformational Isomers

Isomers that differ by rotation around a single (σ) bond.

DEF:Configurational Isomers

Isomers that can only be interconverted by breaking and reforming bonds.

DEF:Enantiomers

Non-superimposable mirror images of each other with opposite stereochemistry at every chiral center.

DEF:Diastereomers

Stereoisomers that are not mirror images of each other.

DEF:Meso Compound

A molecule with chiral centers but an internal plane of symmetry, making it optically inactive.

DEF:Chiral Center

A carbon atom with four different substituents.

DEF:Racemic Mixture

A solution with equal concentrations of two enantiomers, showing no optical activity.

DEF:Optical Activity

The ability of a compound to rotate plane-polarized light.

DEF:Cis-Trans Isomers

Diastereomers differing in position around a double bond or ring; cis

DEF:Axial Substituents

Groups perpendicular to the plane of a cyclohexane ring.

DEF:Equatorial Substituents

Groups in the plane of a cyclohexane ring.

DEF:Angle Strain

Strain caused by deviation of bond angles from ideal values.

DEF:Torsional Strain

Strain caused by eclipsed or gauche conformations.

DEF:Nonbonded Strain

Strain from steric interactions between nonadjacent atoms or groups.

DEF:Newman Projection

A way to visualize the molecule along a C–C bond axis.

DEF:Anti Conformation

A staggered conformation where the two largest groups are 180° apart.

DEF:Gauche Conformation

A staggered conformation where the two largest groups are 60° apart.

DEF:Eclipsed Conformation

A conformation where groups are directly in line with each other in a Newman projection.

DEF:Totally Eclipsed Conformation

A conformation where the two largest groups directly overlap, creating maximum strain.

DEF:Chair Conformation

The most stable conformation of cyclohexane.

DEF:Boat Conformation

A cyclohexane conformation with higher strain than the chair.

DEF:Twist-Boat Conformation

A slightly more stable version of the boat conformation.

DEF:Half-Chair Conformation

Intermediate conformation of cyclohexane during a chair flip.

DEF:Cis

Substituents on the same side of a double bond or ring.

DEF:Trans

Substituents on opposite sides of a double bond or ring.

DEF:E (Entgegen)

Alkene with highest-priority groups on opposite sides of the double bond.

DEF:Z (Zusammen)

Alkene with highest-priority groups on the same side of the double bond.

DEF:Cahn-Ingold-Prelog Priority Rules

A system to assign priority based on atomic number to determine (R)/(S) or (E)/(Z) configurations.

DEF:Fischer Projection

2D representation of a molecule where horizontal lines are wedges and vertical lines are dashes.

DEF:Absolute Configuration

The exact 3D spatial arrangement of substituents around a chiral center.

DEF:Relative Configuration

The stereochemistry of a compound compared to another molecule.

T/F:Structural isomers have identical chemical properties.

False

T/F:Conformational isomers can interconvert without breaking bonds.

True

T/F:Enantiomers have identical chemical properties in achiral environments.

True

T/F:Meso compounds are optically active.

False

T/F:In cyclohexane, bulky groups prefer the equatorial position.

True

T/F:Diastereomers rotate plane-polarized light in equal magnitude but opposite directions.

False

T/F:Anti staggered conformations have lower energy than eclipsed conformations.

True

T/F:Cis-trans isomers are a subtype of diastereomers.

True

T/F:Racemic mixtures show optical activity.

False

T/F:Axial substituents create less steric strain than equatorial.

False

T/F:Newman projections are used to visualize stereochemistry along a C–C bond axis.

True

T/F:Boat conformations are more stable than chair conformations.

False

T/F:Chiral centers require four different substituents.

True

T/F:Switching one pair of substituents in a Fischer projection inverts the stereochemistry.

True

T/F:Rotating a Fischer projection 180° retains stereochemistry.

True

T/F:Rotating a Fischer projection 90° inverts stereochemistry.

True

T/F:Enantiomers rotate plane-polarized light in the same direction.

False

FIB:__ isomers differ only in rotation around a single bond.

Conformational

FIB:Enantiomers rotate plane-polarized light in _ directions.

Opposite

FIB:A molecule with an internal plane of symmetry is called a compound.

Meso

FIB:The largest source of steric strain in cyclohexane boat conformations is interactions.

Flagpole

FIB:Staggered conformations have groups _ degrees apart.

60

FIB:Totally eclipsed conformations are the _ energetic state.

Highest

FIB:The absolute configuration uses the rules to assign priority to substituents.

Cahn-Ingold-Prelog

FIB:(E) configuration of alkenes means the highest-priority substituents are on sides.

Opposite

FIB:(Z) configuration of alkenes means the highest-priority substituents are on sides.

Same

FIB:In Fischer projections, vertical lines go the plane of the page.

Into

FIB:In Fischer projections, horizontal lines come the plane of the page.

Out of

FIB:For a carbon to be a chiral center, it must have different substituents.

Four

FIB:The anti staggered conformation of butane has the two largest groups _ degrees apart.

180

FIB:In the modified Fischer projection method, switching two pairs of substituents _ the stereochemistry.

Retains

FIB:Conformational interconversion barriers are easily overcome at temperature.

Room

FIB:Chiral molecules lack a(n) _ plane of symmetry.

Internal

FIB:A polarizer produces _ light.

Plane-polarized

FIB:Rotation of plane-polarized light to the right is called _.

Dextrorotatory

FIB:Rotation of plane-polarized light to the left is called _.

Levorotatory

FIB:Two molecules that are mirror images but not superimposable are called _.

Enantiomers

FIB:Compounds that differ at some, but not all, chiral centers are _.

Diastereomers

FIB:In a cyclohexane chair flip, axial groups become _.

Equatorial

FIB:In a cyclohexane chair flip, equatorial groups become _.

Axial

DEF:Staggered Conformation

A conformation in which substituents are positioned so that they are as far apart as possible, minimizing torsional strain.

DEF:Eclipsed Conformation

A conformation in which substituents are aligned directly behind each other in a Newman projection, increasing torsional strain.

DEF:Synperiplanar

Substituents that are in the same plane on the same side of a bond, often creating high-energy eclipsed conformations.

DEF:Antiperiplanar

Substituents that are in the same plane but on opposite sides of a bond, often resulting in the most stable staggered conformation.

DEF:Enantiomeric Excess

A measure of the purity of a chiral compound in terms of its deviation from a racemic mixture.

DEF:Configurational Stereoisomers

Isomers that cannot interconvert without breaking covalent bonds and include enantiomers and diastereomers.

DEF:Stereogenic Center

An atom, usually carbon, at which the interchange of two groups produces a stereoisomer.

DEF:Flagpole Interactions

Nonbonded steric interactions in the boat conformation of cyclohexane, causing increased strain.

DEF:Envelope Conformation

Nonplanar conformation of cyclopentane that reduces angle and torsional strain.

DEF:V-shaped Conformation

Nonplanar conformation of cyclobutane, partially alleviating ring strain.

DEF:Twist-Boat Conformation

Intermediate conformation of cyclohexane between chair and boat, slightly reducing steric strain.

T/F:Conformational isomers have different chemical connectivity.

False

T/F:Cis-trans isomers always require a double bond or ring to restrict rotation.

True

T/F:All enantiomers are chiral, but not all chiral molecules are enantiomers.

False

T/F:Anti staggered butane is the lowest-energy conformation because the two largest methyl groups are furthest apart.

True

T/F:Chiral molecules can have a plane of symmetry and still be optically active.

False

T/F:Equatorial substituents in cyclohexane generally experience less steric hindrance than axial substituents.

True

T/F:Diastereomers have identical physical properties.

False

T/F:Switching two substituents on a chiral carbon inverts the absolute configuration.

True

T/F:In a racemic mixture, the rotations of the two enantiomers cancel out, producing no net optical activity.

True

T/F:Optical activity depends on both the concentration of the chiral compound and the path length of the light through the solution.

True

FIB:Conformers with groups 180° apart are called _.

Anti; They are energetically most stable due to minimal torsional strain.

FIB:Conformers with groups 60° apart are called _.

Gauche; They experience moderate steric interactions between the groups.

FIB:The highest-energy conformation, in which the largest groups directly overlap, is _.

Totally Eclipsed; Maximal torsional strain is present.

FIB:Ring strain arises from three sources: , , and _.

Angle strain, torsional strain, nonbonded strain

FIB:In cyclohexane, axial hydrogens or substituents stick _ the plane of the ring.

Perpendicular