Stereoisomerism, Geometrical Isomerism, and Heterocyclic Compounds Flashcards

Vocabulary flashcards covering core concepts of organic stereoisomerism, geometrical isomerism, conformational analysis, and heterocyclic compounds based on lecture notes.

Isomers

Compounds that possess the same molecular formula but differ from each other in physical or chemical properties.

Isomerism

The phenomenon in which two or more compounds possess the same molecular formula but differ in physical or chemical properties due to different modes of combination or arrangement of atoms within the molecule.

Structural Isomerism

Isomerism that occurs when compounds have the same molecular formula but different structural formulas due to differences in the arrangement of atoms within the molecule, without reference to space.

Stereoisomerism

Isomerism exhibited by compounds that have the same structural formula but differ in the spatial arrangement of their atoms or groups (differ in configuration).

Chain Isomers

Structural isomers that possess the same molecular formula but differ in the order in which the carbon atoms are bonded to each other.

Position Isomers

Structural isomers that have the same molecular formula but differ in the position of a functional group on the carbon chain.

Functional Isomerism

A type of structural isomerism where compounds have the same molecular formula but contain different functional groups.

Metamerism

Structural isomerism caused by the unequal distribution of carbon atoms on either side of a functional group among compounds belonging to the same class.

Tautomerism

A phenomenon in which two structural isomers are mutually interconvertible and exist in dynamic equilibrium with each other.

Plane-Polarized Light

Light whose wave vibrations take place in only one single plane perpendicular to the line of propagation.

Optical Activity

The property of a substance capable of rotating the plane of polarized light.

Polarimeter

An instrument consisting of a light source, two lenses (polarizer and analyzer), and a sample tube used to detect and measure optical activity.

Dextrorotatory

A property of an optically active substance that rotates the plane of polarized light to the right (clockwise).

Levorotatory

A property of an optically active substance that rotates the plane of polarized light to the left (counterclockwise).

Specific Rotation

The rotation produced by a solution of length $10\,cm$ and $1\,g/ml$ concentration for a given wavelength of light at a given temperature, calculated as $\text{Specific rotation} = \frac{\text{observed rotation (degrees)}}{\text{Length} \times \text{concentration}}$.

Chiral Carbon

A carbon atom bonded to four different groups or atoms, acting as an asymmetric center in a molecule.

Plane of Symmetry

An imaginary plane that divides an object or molecule into two equal or symmetrical halves.

Enantiomers

Optical isomers that are non-superimposable mirror images of each other and possess identical physical properties except for the direction of rotation of plane-polarized light.

Diastereomers

Stereoisomers that are not mirror images of each other and possess different physical properties and chemical reaction rates.

Meso Compound

A compound containing chiral centers that is optically inactive because its molecules are superimposable on their mirror images, often featuring an internal plane of symmetry.

Racemic Modification

An equal (1:1) mixture of dextro- and levo-enantiomers that is optically inactive because the rotation of one isomer is canceled by the equal and opposite rotation of its enantiomer.

Resolution

The process of separating a racemic mixture into its two individual optically active components ($+$- and $-$-isomers).

Geometrical Isomerism

Isomerism arising due to restricted rotation around a carbon-carbon double bond, where compounds have similar molecular formulas but different spatial arrangements around the double bond.

Cis Isomer

A geometrical isomer in which two similar groups are attached on the same side of the double bond.

Trans Isomer

A geometrical isomer in which two similar groups are attached on opposite sides of the double bond.

Z-Configuration

An E-Z descriptor assigned to a geometrical isomer when the high priority groups attached to double-bonded carbon atoms are on the same side across the double bond.

E-Configuration

An E-Z descriptor assigned to a geometrical isomer when the high priority groups attached to double-bonded carbon atoms are on opposite sides across the double bond.

Conformations

The infinite number of spatial arrangements of atoms in a molecule that arise from free rotation around a single covalent bond without breaking it.

Torsional Strain

The difference in energy between the most stable staggered conformation and the least stable eclipsed conformation in a molecule, resulting from eclipsing bond interactions.

Anti Conformation

The most stable staggered conformation of butane in which the two methyl groups ($-CH_3$) are positioned farthest away from each other.

Gauche Conformation

A staggered conformation of butane (also called skew staggered) in which the two methyl groups are positioned at a dihedral angle of $60^{\circ}$.

Chair Conformation

A strain-free, non-planar conformation of cyclohexane with C-C-C bond angles of $109.5^{\circ}$ in which all C-H bonds are perfectly staggered.

Axial Bonds

Bonds in the chair conformation of cyclohexane that project perpendicular to the ring plane (parallel to the ring axis) and alternate pointing up and down.

Equatorial Bonds

Bonds in the chair conformation of cyclohexane that project outward sideways around the equator of the ring.

1,3-Diaxial Interaction

Steric strain produced in a cyclohexane ring due to steric repulsions between an axial substituent and axial hydrogens located on $C_3$ and $C_5$.

Atropisomerism

A phenomenon where stereoisomers exist as separate, stable chemical species due to restricted rotation about a single covalent bond, typically caused by bulky ortho-substituents in biphenyls.

Heterocyclic Compounds

Cyclic organic compounds whose ring structure contains at least one atom other than carbon, such as nitrogen, oxygen, or sulfur.

Hetero Atoms

Atoms other than carbon, such as nitrogen ($N$), oxygen ($O$), or sulfur ($S$), present as members within a cyclic ring framework.