Chemistry - Chapter 3 - Structure and Stereochemistry of Alkanes

Vocabulary flashcards covering the structure, nomenclature, physical properties, conformations, and ring strain of alkanes and cycloalkanes.

Hydrocarbons

Molecules solely comprised of carbon and hydrogen atoms.

Alkanes

Saturated hydrocarbons containing only single bonds with $sp^3$ hybridized carbons and possessing the general formula $C_n H_{2n+2}$.

Constitutional Isomers

Compounds with the identical molecular formula, but different atom connectivity.

Haloalkanes

Organic compounds named similarly to alkanes where halogen atoms are treated as substituents and named using prefixes fluoro-, chloro-, bromo-, and iodo-.

Catalytic Cracking

An industrial process involving the catalytic conversion of high-boiling long-chain alkanes into shorter-chain alkanes and alkenes using heat and a catalyst.

Catalytic Hydrocracking

The catalytic conversion of long-chain alkanes into shorter-chain alkanes in the presence of hydrogen ($H_2$), heat, and a catalyst.

Conformations

Different spatial arrangements of atoms that result from rotation about a single carbon-carbon \text{\textsigma}-bond.

Conformers

Specific conformations of a molecule that typically cannot be isolated at room temperature due to rapid rotation about single bonds.

Newman Projection

A visual representation method used to view a molecule directly down a specific carbon-carbon bond axis to analyze torsion angles and conformational stability.

Staggered Conformation

A low-energy conformation where the bonds on adjacent carbon atoms are positioned at a $60^\text{o}$ dihedral angle, minimizing electron cloud repulsion.

Eclipsed Conformation

A high-energy conformation where bonds on adjacent carbon atoms align directly with each other, resulting in increased torsional strain.

Torsional Strain

The resistance to rotation caused by electrostatic repulsion between electron pairs in eclipsed bonds on adjacent carbon atoms.

Gauche Conformation

A staggered conformation of butane or other substituted alkanes where two bulky groups (such as methyl groups) have a dihedral angle of $60^\text{o}$ relative to each other.

Anti Conformation

A staggered conformation where two bulky groups lie opposite each other at a dihedral angle of $180^\text{o}$, representing the lowest energy structure.

Totally Eclipsed Conformation

The highest-energy conformation of butane where two methyl groups are eclipsed at a $0^\text{o}$ dihedral angle, experiencing maximum steric strain and torsional strain.

Steric Strain

Interference and repulsion between electron clouds that occurs when two bulky non-bonded groups are forced too close to each other.

Cycloalkanes

Non-polar, saturated ring-containing hydrocarbons with the general molecular formula $C_n H_{2n}$.

Ring Strain

The total strain present in a cyclic molecule, determined by measuring its heat of combustion, consisting of the sum of angle strain and torsional strain.

Angle Strain

Strain caused by sub-optimal orbital overlap when bond angles in a ring are forced to deviate from the ideal tetrahedral angle of $109.5^\text{o}$.

Bent Bonds

Non-linear overlap of $sp^3$ hybrid orbitals occurring in highly strained small rings like cyclopropane, where internal bond angles are compressed to $60^\text{o}$.

Envelope Conformation

A non-planar puckered conformation adopted by cyclopentane to reduce torsional strain from eclipsed adjacent methylene groups.

Chair Conformation

The most stable, strain-free conformation of cyclohexane with alternating carbon atoms, all bond angles equal to $109.5^\text{o}$, and all adjacent bonds fully staggered.

Boat Conformation

A non-planar conformation of cyclohexane with $109.5^\text{o}$ bond angles that suffers from torsional strain due to co-planar eclipsed carbons and steric repulsion between flagpole hydrogens.

Twist Boat Conformation

A non-planar cyclohexane conformation derived by twisting the boat form to reduce flagpole hydrogen interactions and eclipsing of carbon-carbon bonds.

Axial Positions

Positions on a cyclohexane chair conformation that direct bonds vertically straight up or straight down, parallel to the central axis of the ring.

Equatorial Positions

Positions on a cyclohexane chair conformation that direct bonds outward toward the perimeter or equator of the ring.

Chair-Chair Interconversion

The ring-flip process in cyclohexane where the ring converts between two chair forms, causing all axial substituents to become equatorial and all equatorial substituents to become axial.

1,3-Diaxial Interactions

Steric interference and strain occurring between an axial substituent and axial hydrogen atoms or groups on the C3 and C5 positions of a cyclohexane chair ring.

Bicyclic Ring Classifications

The three structural classes of bicyclic ring systems: fused bicyclic (sharing two adjacent carbons), bridged bicyclic (sharing two nonadjacent bridgehead carbons), and spirocyclic (sharing a single common carbon).

Decalin

A fused bicyclic alkane consisting of two fused cyclohexane rings, existing as cis-decalin (one axial, one equatorial ring junction) or trans-decalin (diequatorial ring junction) isomers.