Are alkynes weakly polar?

I was reading about physical properties of alkynes in my [Chemistry textbook](https://ncert.nic.in/textbook/pdf/kech206.pdf).


One of the sentence states



> 
> Alkynes are weakly polar in nature.
> 
> 
> 


I didn't understand how alkynes are weakly polar, so I tried to search about it on the internet but couldn't find any explanation.


Many sites (like [this](https://www.angelo.edu/faculty/kboudrea/molecule_gallery/03_alkynes/00_alkynes.htm) and [this](https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Supplemental_Modules_(Organic_Chemistry)/Alkynes/Properties_of_Alkynes)) rather state that alkynes are non-polar.


My question is: are alkynes weakly polar? If yes, why?




Yes, alkynes can display a (small) permanent electric dipole moment, and thus are polar molecules by the usual definition. For example see <https://cccbdb.nist.gov/exp2x.asp?casno=74997&charge=0> where the dipole moment for propyne is given as 0.780 Debye. Given such a molecule is asymmetric is it shouldn't be a surprise that there is a dipole moment.


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