Question

How can `"E/Z"` isomers arise?

Answer 1

Consider the simple molecule `"2-butylene..........."`

Explanation:

Now for `H_3C-CH=CH-CH_3` we can have 2 geometric isomers:

`"cis-2-butylene"` or `"Z-butene"`; or `"trans-2-butylene"` or `"E-butene"`

For both isomers, the connectivity is MANIFESTLY the same: `C1` connects to `C2` connects......to `C4`. However, the geometry is manifestly different, and this geometric isomerism gives rise to different physical and chemical properties.

For example, `"cis-2-butene"` has a boiling point of `3.7` `""^@C`; on the other hand, `"trans-2-butene"` has a boiling point of `0.9` `""^@C`;