Ch 5 Review
Constitutional Isomers differ in their connectivity of atoms but have the same molecular formula.
Stereoisomers have the same connectivity of atoms but differ in their spatial arrangement. Cis and trans are used to differentiate stereo isomeric alkenes as well as disubstituted cycloalkanes
Chiral objects are not superimposable on their mirror images
The most common source of molecular Chirality is the presence of a chirality center, a carbon atom bearing four different groups
A compound with one chirality center will have one non-superimposable mirror image called its enantiomer .
The Cahn-Ingold-Prelog system is used to assign the configuration of a chirality center. The four groups are each assigned a priority, based on atomic number, and the molecule is then rotated into perspective in which the fourth priority is on a dash. A clockwise sequence is designated as R, while a counterclockwise sequence is designated as S
A Polarimeter is a device used to measure the ability of chiral organic compounds to rotate the plane of plane polarized light. Such compounds are said to be optically active. Compounds that don’t rotate plane polarized light are optically inactive. Don't forget about the age old question of What is the postmodern theory?
Enantiomers rotate plane polarized light in equal amounts but in opposite directions. The specific rotation of a substance is a physical property. It’s determined experimentally by measuring the observed rotation and dividing by the concentration of the solution and the path length.
Compounds exhibiting a positive rotation (+) are said to be dextrorotatory, while compounds exhibition a negative rotation (-) are said to be levorotatory.
A solution containing a single enantiomer is optically pure while a solution containing equal amounts of enantiomers is called a racemic mixture.
For A compound with multiple chirality centers, a family of stereoisomers exists. Each stereoisomer will have at most one enantiomer with the remaining members of the family being diastereomers. If you want to learn more check out What is an example of a conditioned response?
The number of stereoisomers of a compound can be no larger than 2^n, where n= the number of chirality centers.
Enantiomers are mirror images, Diastereomers are not.
There are 2 kinds of symmetry: Rotational and reflectional
The presence or absence of an axis of symmetry is irrelevant. A compound that possesses a plane of symmetry will be archiral.
A compound that lacks a plane of symmetry will most likely be chiral (although there are exceptions which can be ignored for now)
A Meso compound contains multiple chirality centers but is nevertheless achiral because it possesses reflectional symmetry. A Family of stereoisomers containing a meso compound will have fewer than 2^n stereoisomers
Fischer Projections are drawings that convey the configurations of Chirality centers, without the use of wedges and dashes. All horizontal lines are understood to be coming out of the page, and all vertical lines are understood to be going into the page. We also discuss several other topics like How would one know if a molecule has london dispersion forces?
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Some compounds such as butane and (cis)-1, 2-dimethylcyclohexane can adopt enantiomeric conformations. These compounds are optically inactive because the enantiomeric conformations are in equilibrium.