# How can "E/Z" isomers arise?

Feb 2, 2017

Consider the simple molecule $\text{2-butylene...........}$

#### Explanation:

Now for ${H}_{3} C - C H = C H - C {H}_{3}$ we can have 2 geometric isomers:

$\text{cis-2-butylene}$ or $\text{Z-butene}$; or $\text{trans-2-butylene}$ or $\text{E-butene}$

For both isomers, the connectivity is MANIFESTLY the same: $C 1$ connects to $C 2$ connects......to $C 4$. However, the geometry is manifestly different, and this geometric isomerism gives rise to different physical and chemical properties.

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