♦ Tension $\equiv CH$: 3300 $cm^{-1}$
♦ Tension $-C\equiv C-$: 2150 $cm^{-1}$. Symmetrical alkynes do not present this band, being very weak in the internal ones. The conjugation lowers the value slightly.
IR spectrum of 1-hexine
In the spectrum, in addition to the characteristic bands of the alkyne, the CH tension bands of the chain (below 3000) and the scissor bending bands of CH 2 (1467) and those of symmetric and asymmetric bending of methyl are observed. .
IR spectrum of 2-hexine
2-Hexyne is an internal alkene and does not show the CH$\equiv band at 3300 $cm^{-1}$. It also presents a very weak $C\equiv C$ voltage band, due to its poor polarity.
IR spectrum of phenylacetylene
Conjugation lowers the value of the frequency at which the tension band $C\equiv C$ appears
