Klein Organic Chemistry End of Chapter Vocabulary

Alkane

A saturated hydrocarbon containing only carbon–carbon single bonds.

Saturated hydrocarbon

A hydrocarbon that contains no π bonds.

Cycloalkane

A saturated hydrocarbon containing one or more carbon rings.

Parent compound

The longest continuous carbon chain or principal ring used as the basis for naming a molecule.

Substituent

An atom or group attached to the parent structure.

Alkyl group

A group formed by removing one hydrogen atom from an alkane.

Nomenclature

The system of rules used to assign names to chemical compounds.

Systematic name

A name assigned according to standardized IUPAC rules.

Common name

A traditional name that remains in use despite the existence of a systematic alternative.

Complex substituent

A branched alkyl group attached to the parent structure.

Locant

A number indicating the position of a substituent on the parent structure.

Alphabetizing rule

Multiplicative prefixes such as di-, tri-, tetra-, penta-, and hexa- are ignored when arranging substituents alphabetically.

Constitutional isomer

A compound with the same molecular formula but a different connectivity of atoms.

Conformation

A three-dimensional arrangement of atoms produced by rotation about single bonds.

Rotation about single bonds

Motion that allows different spatial arrangements without breaking bonds.

Newman projection

A drawing method that views a molecule along a carbon–carbon single bond.

Dihedral angle

The angle describing the relative positions of groups attached to adjacent carbon atoms.

Torsional angle

Another name for the angle describing the relative orientation of groups across a single bond.

Staggered conformation

A low-energy arrangement in which bonds on adjacent carbons are offset.

Eclipsed conformation

A higher-energy arrangement in which bonds on adjacent carbons align.

Torsional strain

Increased energy resulting from eclipsing interactions between bonds.

Anti conformation

The lowest-energy staggered arrangement in which the largest groups are opposite each other.

Gauche conformation

A staggered arrangement in which the largest groups are separated by approximately 60°.

Gauche interaction

Repulsive interaction between large groups separated by approximately 60°.

Angle strain

Increased energy caused by deviation of bond angles from the preferred tetrahedral value.

Chair conformation

The lowest-energy arrangement of a six-membered saturated ring with minimal strain.

Boat conformation

A higher-energy arrangement containing eclipsing interactions and steric crowding.

Twist-boat conformation

A distorted version of the boat arrangement that reduces eclipsing interactions.

Axial position

A bond orientation approximately perpendicular to the average plane of the ring.

Equatorial position

A bond orientation extending roughly around the perimeter of the ring.

Ring flip

Conversion of one chair arrangement into the other.

1,3-Diaxial interaction

Steric repulsion between an axial substituent and axial groups located two carbons away.

Preferred position for a single substituent

The orientation that minimizes steric interactions.

cis relationship

Similar groups located on the same side of a ring.

trans relationship

Similar groups located on opposite sides of a ring.

UP orientation

A three-dimensional direction pointing above the average plane of the ring.

DOWN orientation

A three-dimensional direction pointing below the average plane of the ring.

Behavior of UP/DOWN during ring flip

The three-dimensional orientation remains unchanged.

Energy comparison of chair conformations

Determined by the total steric cost of substituents occupying perpendicular positions.

Preferred tetrahedral bond angle

Approximately 109.5°.

Total ring strain

The combined effects of angle strain and torsional strain.

Ring strain assessment

Comparison of heats of combustion per CH₂ group.

Highest-energy butane eclipsed conformation

The arrangement in which the two methyl groups eclipse one another.

Propane torsional strain

Greater than that of ethane.

Ethane staggered conformations

All have identical energy.

Ethane eclipsed conformations

All have identical energy.

Degenerate conformations

Different arrangements that possess identical energy.

Source of torsional strain

Repulsion between bonding electron pairs in eclipsed arrangements.

Effect of a ring flip

Groups that are perpendicular become peripheral, and vice versa, while retaining their three-dimensional orientation.

Number of substituent positions per cyclohexane carbon

Two.

Monosubstituted cyclohexane equilibrium

Interconversion occurs between arrangements with the group in different positions.

Reason equatorial positions are favored

They avoid steric repulsions present in the alternative orientation.

Flagpole interaction

Steric repulsion between atoms positioned across the boat arrangement.

Most common cyclohexane conformation

The lowest-energy arrangement with minimal strain.

Stability comparison using combustion

Lower measured energy release indicates greater stability among isomers.

Heat of combustion

The negative of the enthalpy change associated with complete combustion of one mole of a compound in oxygen.

Enthalpy change

The heat absorbed or released during a process at constant pressure.

Constitutional isomer

A compound with the same molecular formula but a different connectivity of atoms.

Stereoisomer

A compound with the same connectivity of atoms but a different spatial arrangement.

cis relationship

Similar groups located on the same side of a double bond or ring.

trans relationship

Similar groups located on opposite sides of a double bond or ring.

Chiral object

An object that is not superimposable on its mirror image.

Chiral center

A tetrahedral carbon atom bonded to four different groups.

Chirality center

A tetrahedral carbon atom bonded to four different groups.

Enantiomer

One member of a pair of nonsuperimposable mirror-image molecules.

Cahn–Ingold–Prelog system

A set of rules used to assign configurations based on group priorities.

Priority rule

Groups are ranked according to atomic number.

R configuration

The designation assigned when the sequence of priorities 1→2→3 is clockwise after placing the lowest-priority group away from the viewer.

S configuration

The designation assigned when the sequence of priorities 1→2→3 is counterclockwise after placing the lowest-priority group away from the viewer.

Diastereomer

A stereoisomer that is not the mirror image of another stereoisomer.

Relationship between enantiomers

They are nonsuperimposable mirror images.

Relationship between diastereomers

They are stereoisomers that are not mirror images.

Maximum number of stereoisomers

No greater than 2ⁿ, where n is the number of chiral centers.

Plane of symmetry

A mirror plane that divides a structure into two identical halves.

Reflectional symmetry

The property of possessing a mirror plane.

Achiral compound

A molecule that is superimposable on its mirror image.

Chiral compound

A molecule that is not superimposable on its mirror image.

Meso compound

A molecule containing multiple chiral centers that is nevertheless achiral because of internal mirror symmetry.

Reason meso compounds are achiral

Internal mirror symmetry makes the molecule superimposable on its mirror image.

Fischer projection

A drawing convention in which horizontal bonds project toward the viewer and vertical bonds project away.

Horizontal bonds in a Fischer projection

Bonds directed toward the viewer.

Vertical bonds in a Fischer projection

Bonds directed away from the viewer.

E descriptor

Indicates that the highest-priority groups are on opposite sides of a double bond.

Z descriptor

Indicates that the highest-priority groups are on the same side of a double bond.

When to use E/Z notation

For trisubstituted and tetrasubstituted alkenes.

Heat of reaction

The total enthalpy change (ΔH) for a reaction representing energy exchanged between system and surroundings.

Bond dissociation energy

The energy required to homolytically break a bond into radicals.

Exothermic reaction

A process in which energy is released from the system to the surroundings.

Endothermic reaction

A process in which energy is absorbed from the surroundings into the system.

Entropy

A thermodynamic quantity describing system dispersal of energy and number of accessible microstates.

Spontaneous reaction (entropy criterion)

A process for which the total entropy change of system and surroundings is positive.

Gibbs free energy

A thermodynamic potential whose change determines spontaneity of a process.

Exergonic reaction

A process with negative Gibbs free energy change (spontaneous under constant T, P).

Endergonic reaction

A process with positive Gibbs free energy change (nonspontaneous under standard conditions).

Thermodynamics

The study of energy changes and equilibrium positions in chemical systems.

Equilibrium state

The lowest free-energy configuration of a system.

Equilibrium constant

A value describing the ratio of products to reactants at equilibrium.

ΔG–Keq relationship

Negative ΔG corresponds to Keq > 1; positive ΔG corresponds to Keq < 1.

Kinetics

The study of reaction rates and mechanisms.

Rate law

An equation relating reaction rate to reactant concentrations.