# Question #bdebe

May 26, 2017

Actually I think, the question refers to the priority preference during nomenclature of hydrocarbon containing both carbon-carbon double bond $\left(C = C\right)$and carbon-carbon triple bond $\left(C \equiv C\right)$.

The general rule is that any unsaturation $\left(C = C\right) \mathmr{and} \left(C \equiv C\right)$ to be preferred during placing locants (numbering) i.e to have minimum locant.

But if both $\left(C = C\right) \mathmr{and} \left(C \equiv C\right)$ occupy same position counting from opposite ends then $\left(C = C\right)$ to be given minimum locant and 'yne' suffix for $\left(C \equiv C\right)$. is always followed by 'en' suffix for $\left(C = C\right)$ to be added after the stem/root name.

Example

1.$\stackrel{6}{C} {H}_{3} \stackrel{5}{C} H = \stackrel{4}{C} H \stackrel{3}{C} {H}_{2} \stackrel{2}{C} \equiv \stackrel{1}{C} H$
Here the unsaturation $\left(C \equiv C\right)$ gets minimum locant if numbered from right. So the name becomes, $\text{hex-4-en-1-yne}$

2.$\stackrel{6}{C} {H}_{3} \stackrel{5}{C} \equiv \stackrel{4}{C} \stackrel{3}{C} {H}_{2} \stackrel{2}{C} H = \stackrel{1}{C} {H}_{2}$
Here the unsaturation $\left(C = C\right)$ gets minimum locant if numbered from right. So the name becomes, $\text{hex-1-en-4-yne}$

3 . $\stackrel{1}{C} {H}_{2} = \stackrel{2}{C} H \stackrel{3}{C} {H}_{2} \stackrel{4}{C} {H}_{2} \stackrel{5}{C} \equiv \stackrel{6}{C} H$
Here bot the unsaturation $\left(C = C\right) \mathmr{and} \left(C \equiv C\right)$ get minimum locant(1), if numbered from left and right. Here the preference should be given to $\left(C = C\right)$ and numbering from left will be correct.

So the name becomes, $\text{hex-1-en-5-yne}$