Chapter 10 PDF

Preview

Summary

These are detailed lecture notes for chapter 10 from physiological chemistry II....

Description

Chapter 10: Things You Need to Know for the Exam *Quiz 4* Helpful Links ➔ Types of Isomers: Constitutional Isomers, Stereoisomers, Enantiomers, and Diastereomers: https://www.masterorganicchemistry.com/2018/09/10/types-of-isomers/

1.) Know the structural requirements for chirality and achirality, as well as how to identify compounds that are chiral versus achiral, including the structural characteristics that lead to meso compounds ● An asymmetric object, which cannot be identical to its mirror image, is said to be chiral (pronounced ‘ky-rull’)

●

An object that has a plane of symmetry is identical to its mirror image and is achiral ○ Achiral objects cannot have an enantiomer because they are identical (i.e., superimposable) to their mirror image

●

Chirality most commonly arises when an atom with tetrahedral electron group geometry is bonded to FOUR different structures ○ These atoms are called a chiral center or chirality center ■ A molecule having one and only one chiral center MUST be chiral

●

Meso structures - the presence of chiral elements in a molecule or object does NOT guarantee its chirality because the molecule or object may still have symmetry as a whole ○ SAME MOLECULE; NOT an enantiomer

2.) Know how to identify and distinguish, constitutional isomers, enantiomers, and diastereomers, including epimers, as well as compounds that are NOT isomers of each other, if given examples

Stereochemistry Stereoisomers

Isomers that have identical order of connectivity of atoms, but they differ in their spatial (i.e., three-dimensional) orientation ● Types of stereoisomers: enantiomers and diastereomers

Constitutional Isomers Isomers that have the same molecular formula, but different connectivities; have same empirical formulae but their core IUPAC names are different

Enantiomers

Stereoisomers that are non-superimposable (non-identical) mirror images of each other; they cannot be superimposed on top of one another ● Are variants of the same compounds that have nearly identical chemical and physical properties ● Lack a plane of symmetry ● Since they are mirror images, they must exist in pairs ○ Any asymmetric object can have one and only ONE enantiomer

Diastereomers

Aka geometric isomers; arise when groups bonded to distinct atoms are constrained to different relative spatial orientations via restricted rotations

●

When two groups are oriented toward the same side of the axis joining the bonded atoms, they are in a cis relative orientation ● Alternatively, when two groups are oriented toward the opposite side of the axis joining the bonded atoms, they are in a trans relative orientation In general, with molecules having multiple chirality centers ● Diastereomers arise when at least ONE but NOT ALL of the chirality centers in a molecule have a different configuration ● When ALL chirality centers in a chiral molecule exhibit a change in the relative arrangement of its groups, its enantiomer results

Epimers

Chiral diastereomers that differ in ONLY ONE chiral center are called epimers

3.) Know how to determine the number of chiral centers in a structure and the number of possible stereoisomers that can arise ● When a molecule has ‘n’ chirality centers , it can exist as up to 2^n structurally different asymmetric stereoisomers ○

They will exist as ½ × 2^n pairs of enantiomers ■ When meso stereoisomers exist, the number of stereoisomers is less than 2n, because the meso compounds do not have an enantiomer...