The properties of alkenes depend on their geometry

You have met alkenes participating in reactions in a number of chapters, but our discussion of how to make alkenes has so far been quite limited, Chapter 19 was about elimination reactions, and there you met El and E2 reactions. 

In Chapter 14, you met an important reaction known as the Wittig reaction, which also forms alkenes. 

These two compounds, ( )-and (E)-dimethyl but-2-enedioate, are commonly known as dimethyl maleate and dimethyl fumarate. They provide a tel ling exam pie of how different the physical properties of geometrical isomers 

In this chapter we shall talk about reactions similar to the ones on the previous page and we shall be interested in how to control the geometry of double bonds. Geometrical isomers of alkenes are different compounds with different physical, chemical, and biological properties. They are often hard to separate by chromatography or distillation, so it is important that chemists have methods for making them as single isomers. 

The activity of the fungicide diniconazole is dependent on the geometry of its double bond the -isomer disrupts fungal metabolism, while the Z-isomer is biologically inactive. 

These two compounds, (Z)- and )-dimethyl but-2- can be. Dimethyl maleate is a liquid with a boiling point of 

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