optical isomers

Examples of optical isomers in the following topics:

• Organic Enantiomers

  • Stereoisomers are a type of isomer where the order of the atoms in the two molecules is the same but their arrangement in space is different.
  • The two main types of stereoisomerism are diastereomerism (including 'cis-trans isomerism') and optical isomerism (also known as 'enantiomerism' and 'chirality').
  • Enantiomers are two optical isomers (i.e. isomers that are reflections of each other).
  • Every stereocenter in one isomer has the opposite configuration in the other.
  • Compounds that are enantiomers of each other have the same physical properties except for the direction in which they rotate polarized light and how they interact with different optical isomers of other compounds.

• Isomers in Coordination Compounds

  • As with other compounds, there are several kinds of coordination complex isomers.
  • An example of cis and trans isomers can be seen for platin.
  • When three identical ligands occupy one face of an octahedron, the isomer is said to be facial, or fac.
  • In a fac isomer, any two identical ligands are adjacent or cis to each other.
  • If you shine light through pure solutions of each optical isomer they would rotate the plane of polarized light in opposite directions.

• General Summary of Isomerism and Molecular DescriptorsInclude Relationship of Constitutional and Stereoisomers and Relationships of Stereoisomers

  • All the 1,2-dichloro isomers are constitutional isomers of the 1,3-dichloro isomers.
  • In each category (1,2- & 1,3-), the (R,R)-trans isomer and the (S,S)-trans isomer are enantiomers.
  • The cis isomer is a diastereomer of the trans isomers.
  • Since the cis isomer has two centers of chirality (asymmetric carbons) and is optically inactive, it is a meso-compound.
  • These isomers are diastereomers of each other, and are constitutional isomers of the 1,2- and 1,3- isomers.

• Compounds Having Two or More Chiral Centers

  • Both compounds are stereoisomers of 2-methylamino-1-phenyl-1-propanol, and both are optically active, one being levorotatory and the other dextrorotatory.
  • How, then, are we to classify these isomers and others like them?
  • Since these two compounds are optically active, each must have an enantiomer.

• Optical Activity

  • This perturbation is unique to chiral molecules, and has been termed optical activity.
  • Compounds that rotate the plane of polarized light are termed optically active.
  • Each enantiomer of a stereoisomeric pair is optically active and has an equal but opposite-in-sign specific rotation.
  • A 50:50 mixture of enantiomers has no observable optical activity.
  • Chiral organic compounds isolated from living organisms are usually optically active, indicating that one of the enantiomers predominates (often it is the only isomer present).

• The Nonclassical Carbocation Hypothesis

  • As shown in the following diagram, the rate of acetolysis of the exo-isomer is substantially faster than that of the endo-isomer, which reacts at a rate similar to the cyclohexyl derivative.
  • The former substitution proceeds with complete retention of configuration and racemization; whereas the endo-isomer is substituted with inversion of configuration and retains a small degree of optical activity.
  • By comparison, the endo-isomer ionizes to a classical 2º-carbocation, which is rapidly converted to the more stable nonclassical ion.
  • Some acetate anion may bond to the 2º-carbocation before it changes, accounting for the residual optical activity in this reaction.
  • Brown pointed out that the norbornyl compounds are better compared with cyclopentyl than with cyclohexyl analogs (eclipsing strain), and in such a comparison the endo isomer is abnormally slow, the exo isomer being only 14 times faster than cyclopentyl.

• Enantiomers and Stereoisomerism in Organic Compounds

  • Stereoisomers are isomers in which bond connectivity is the same, but spatial arrangement of the bonds differs.
  • Stereoisomers, or spatial isomers, are specific types of isomers.
  • Stereoisomers of a compound have not only the same chemical formula as one another (as do all isomers), but the same bond connectivity.
  • Some stereoisomers are not optically active and are actually exactly the same molecule.
  • The (R, R) and (S, S) isomers are enantiomers.

• Achiral Diastereomers (Meso-Compounds)

  • Meso compounds are achiral (optically inactive) diastereomers of chiral stereoisomers.
  • Some physical properties of the isomers of tartaric acid are given in the following table.
  • Fischer projection formulas provide a helpful view of the configurational relationships within the structures of these isomers.

• Isomers

  • Different compounds having the same molecular formula are called isomers, and the prevalence of organic isomers reflects the extraordinary versatility of carbon in forming strong bonds to itself and to other elements.
  • When the group of atoms that make up the molecules of different isomers are bonded together in fundamentally different ways, we refer to such compounds as constitutional isomers.
  • The three C5H12 isomers shown below illustrate these terms.
  • Considering that molecules are much too small to be seen by even the strongest optical microscopes, how is it that the connectivity and relative location of the component atoms can be assigned with confidence?
  • The top row shows isomers in which an electronegative chlorine is attached to a butyl group.

• Optic (II) Nerve

  • The optic nerve (cranial nerve II) receives visual information from photoreceptors in the retina and transmits it to the brain.
  • The optic nerve is also known as cranial nerve II.
  • Each human optic nerve contains between 770,000 and 1.7 million nerve fibers.
  • As a consequence, optic nerve damage produces irreversible blindness.
  • The optic nerve leaves the orbit, which is also known as an eye socket, via the optic canal, running postero-medially toward the optic chiasm, where there is a partial decussation (crossing) of fibers from the nasal visual fields of both eyes.