Isomers diastereomers

Stereo isomers have the same constitution, but a different spatial arrangement of their atoms they differ in their configuration. Two cases have to be distinguished geometric isomers (diastereomers) and enantiomers. 

Some nomenclature note that in the trans isomer, the two methyl groups are on opposite sides of the double bond, or across from each other. In the cis isomer, they are on the same side of the double bond. Like constitutional isomers, diastereomers have different physical and chemical properties. 

Non-polar supports like polystyrene/divinylbenzene copolymers or carbon are also used as column materials. Alumina is polar and acidic while TiOi, and zirconia are much more neutral. They all have good aqueous stability compared to silica. Normal phase chromatography is restricted to the separation of stereochemical isomers, diastereomers, low molecular weight aromatic compounds and functionalized long chain aliphatic compounds. 

The three geometric isomers (diastereomers) for M(AAAA)B2 complexes, one of which is of trans geometry with respect to the two simple ligand B (centre), and two of which are of cis geometry (cis-ft at left, cis-a at right) and in those cases have enantiomers, also drawn. 

Am. (a) Constitutional isomers (b) cis-tram isomers which are also categorized as optical isomers (diastereomers) (c) enantiomers (d) different compounds which are not isomers (e) enantiomers (/) same compound (g) cis-tram isomers (diastereomers). 

CD-containing mobile phases in HPLC have been successfully used for the separation of various isomers such as structural isomers, diastereomers and enantiomers. For example, ortho, meta, para isomers of cresol, xylene and aU six isomers of nitrocinnamic acid were separated on the Lichrosorb RP-C18 column with jS-CD solution as mobile phase [41]. Similar results were also obtained for ortho, meta and para isomers of nitrophenol, nitroaniline, fluoronitrobenzene. 

Therefore, they cannot exist as enantiomers. Instead, we call these isomers diastereomers. 

Ergot alkaloids that contain a C9 = CIO double bond readily undergo reversible epimerization at the asymmetric carbon atom in the 8 position in the lysergic acid part of the molecule to produce a mixture of left-hand rotational isomers with the C-8-(R) configuration which are called ergopeptines, and right-hand rotational (S)-isomers diastereomers called ergopeptinines, as shown in Fig. 35.2. 

Co-crystals of Alike Molecules (including Enantiomers, Isomers, Diastereomers. ..)... 

Consider the following pairs of structures. In each case, are the structures different conformers or are they isomers If they are isomers, then state whether they are constitutional isomers, diastereomers, or enantiomers. 

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