Stereochemistry in Bio-organics Flashcards

Practice flashcards covering definitions of stereochemistry, chirality, R/S nomenclature, projection methods, and biological stereospecificity based on the lecture transcript.

What is the definition of stereochemistry?

The branch of chemistry which deals with the three-dimensional structure of molecules and their effect on physical and chemical properties.

How are constitutional (structural) isomers defined?

Different compounds that have the same molecular formula but different bonding sequences (atom connectivity).

What are stereoisomers?

Molecules with the same molecular formula and bonding sequence but different spatial orientations of their atoms.

What is the fundamental requirement for a molecule to be represented as a three-dimensional object?

It needs at least one carbon atom that is $sp^3$-hybridized.

Define enantiomers.

Stereoisomers that are nonsuperimposable mirror images of each other.

What are diastereomers?

Stereoisomers that are not mirror images of each other, including configurational and cis-trans varieties.

What geometric property defines chirality?

The property of an object (molecule) being non-superimposable on its mirror image, also known as "handedness."

What is an achiral object?

An object that is superimposable on its mirror image, making the object and its mirror image identical.

What are the alternative names for a chiral carbon atom?

'Stereogenic carbons' or 'asymmetrical carbon atoms.'

What is a plane of symmetry (mirror plane) and its effect on chirality?

A plane that divides a molecule into two exact mirror-image halves; a molecule possessing one is achiral even if it contains asymmetric carbon atoms.

What are meso compounds?

A specific subset of achiral molecules that contain chiral centers (stereocenters) but are optically inactive due to an internal plane of symmetry.

Who discovered molecular chirality in 1848?

Louis Pasteur, who separated the two isomers of sodium ammonium tartarate.

What is plane polarized light?

Light whose vibrations occur in only one plane after passing through a polarizing Nicol prism.

Define dextrorotatory and laevorotatory.

Dextrorotatory ($d$ or $+$) describes a compound that rotates plane polarized light clockwise (to the right); laevorotatory ($l$ or $-$) describes a compound that rotates it anticlockwise (to the left).

What is the formula for calculating specific rotation $[\alpha]$?

$[\alpha]^t_\lambda = \frac{\theta}{l \times c}$ where $\theta$ is the observed angle of rotation, $l$ is the length of the sample tube in decimeters, and $c$ is the concentration in $g/mL$.

What does the Cahn-Ingold-Prelog convention (R) and (S) designate?

The absolute configuration around a chiral carbon, where (R) stands for rectus (right) and (S) stands for sinister (left).

Describe the Step I Sequence Rule for R/S priority assignment.

Priority depends on atomic number; the atom directly attached to the chiral center with the highest atomic number receives priority (1), while the lowest receives (4).

According to CIP Rule 2, how is priority assigned among isotopes?

The isotope with the higher mass receives the higher priority (e.g., $^3H > ^2H > ^1H$).

How does one determine (R) vs (S) configuration after prioritizing ligands?

View the molecule with the lowest priority group (4) pointing away; if the sequence 1 to 2 to 3 is clockwise, it is (R), if anticlockwise, it is (S).

In a Fischer projection, where is the most oxidized carbon typically placed?

At the top of the vertical carbon chain.

What do horizontal and vertical lines represent in a Fischer projection?

Horizontal bonds point towards the observer (above the plane of the paper), while vertical bonds point away from the observer (below the plane).

Define prochirality.

The property of an achiral molecule or group that can be transformed into a chiral molecule or group through a single chemical modification.

What are Re and Si faces in trigonal planar systems?

Faces used to distinguish sides of a molecule; Re is assigned if the priority sequence 1-2-3 is clockwise, and Si if it is counterclockwise.

Distinguish between homotopic, enantiotopic, and diastereotopic substituents.

Homotopic substituents are identical when replaced by another group; enantiotopic replacement results in enantiomers; diastereotopic replacement results in diastereomers.

How do (R)-limonene and (S)-limonene differ in nature?

The (R)-enantiomer smells like oranges, while the (S)-enantiomer smells like lemons.

What is a teratogen?

An agent that can disturb the development of the embryo or fetus.