Stereoisomers isomers

Since all the physical properties of two given enantiomers are the same in the absence of a chiral, or optically active, medium, their chromatographic resolution needs a different approach from the relatively simple separation of geometrical isomers, stereoisomers or positional isomers. Two methods are used. The older technique of indirect resolution, requires conversion of the enantiomers to diastereoisomers using a suitable chiral reagent, followed by separation of the diastereoisomers on a non-chiral GC or LC stationary phase. This technique has now been largely superseded by direct resolution, using either a chiral mobile phase (in LC) or a chiral stationary phase. A variety of types of chiral stationary phase have been developed for use in GC, LC and SFC(21 23). 

OPTICAL ISOMER- Either of two kinds of optically active three-dimensional isomers (stereoisomers). One kind is represented by mirror-image presence of one or more asymmetric carbon atoms in the compound (glyceraldehyde, lactic acid, sugars, tartaric add, amino acids). The other kind is exemplified by diastereoisomers, which are not mirror images. These occur in compounds having two or more asymmetric carbon atoms thus, such compounds have 2 optical isomers, where n is the number of asymmetric carbon atoms. 

Two molecules with the same molecular formula and the same bond-to-bond connectivity that are not the same compound are called stereoisomers. Unless they are geometric isomers, stereoisomers must each contain at least one chiral center in the same location. There are two types of stereoisomers enantiomers and diastereomers. 

In Chapter i you learned the geometry of the bonds around an atom. For example, the four bonds of an -hybridized carbon have a tetrahedral geometry. But what happens when several such carbons are bonded together What is the geometrical relationship between the bonds on different carbons What is the overall shape of the molecule Is more than one shape possible If so, are they different in energy Can they interconvert If so, how fast These and other questions will be answered in this chapter and the next, which discuss the stereochemistry, or three-dimensional structures, of organic molecules. In these chapters you will encounter a new type of isomer stereoisomers. Unlike the constitutional isomers that you have already seen, stereoisomers have the same bonds or connectivity, but the bonds are in a different three-dimensional orientation. 

Optical Isomer Stereoisomers other than geometric (cis-trans) isomers that include substances that can rotate the plane of plane polarized light. 

Classify each pair of compounds as constitutional isomers, stereoisomers, identical molecules, or not isomers of each other, and I I... 

Label each pair of aikenes as constitutional isomers, stereoisomers, or identical. 

Within the same series, the branched chain isomer generally has greater lipid solubility, hypnotic activity, and shorter duration of action than the straight chain isomer. Stereoisomers have approximately equal potencies. 

Optical isomers Stereoisomers that rotate the plane of plane polarized light. 

We have already seen (in Section 3.1) that some molecules are not super-imposable on their mirror images and that these mirror images are optical isomers (stereoisomers) of each other. A chiral (asymmetric) carbon atom is the usual source of optical isomerism, as was the case with amino acids. The simplest carbohydrate that contains a chiral carbon is glyceraldehyde, which... 

Enantiomers Stereoisomers whose molecule structures mirror each other at one or more asymmetrical carbon atoms (also called isomers, stereoisomers see also racimers, epimers). 

Isomers are chemical compounds with the same molecular formula, but which are different in some way. The major lypes are constitutional isomers, stereoisomers, and enantiomers (the last one is actually a subset of the second-to-last one, but we ll get there in a minute). 

Cis isomers Stereoisomers with groups on the same side of a carbon-carbon double bond... 

Stereoisomers (Sections 1.13B, 4.9A, 4.13, 5.2B, and 5.14) Compounds with the same molecular formula that differ only in the arrangement of their atoms in space. Stereoisomers have the same connectivity and, therefore, are not constitutional isomers. Stereoisomers are classified further as being either enantiomers or diastereomers. 

For some compounds, knowing the molecular formula and the bond connectivity is still not enough to uniquely specify the identity of an isomer. Stereoisomers are compounds that have identical molecular formulas and identical bond connectivity, but have different three-dimensional structures. There are two types of stereoisomers geometric isomers and optical isomers. 

Cis,trans isomers Stereoisomers that have the same connectivity of their atoms... 

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