# What is the molecular formula of 2-ethynyloctahydro-1H-indene?

I thought the formula for this $$\ce{C11H15}$$, but it's not. I need assistance in finding the proper formula:

• You forgot the $\ce{H}$ on the triple bond! :-) – Mathew Mahindaratne Feb 16 '19 at 6:16

I suspect you forgot one hydrogen at the terminal carbon in alkyne group $$\ce{R-C#C-H}$$. With this in mind the formula would be $$\ce{C11H16}$$: