Answer:
Terminal alkynes \[(R-C\equiv C-H)\]
are weakly acidic in nature because of \[sp\]-hybridised state of the triple
bonded carbon atom. Due to substantial \[s\]-character (50%), the triple bonded
carbon is electronegative in nature and this enables the release of \[{{H}^{+}}\]
ion from \[\equiv C-H\] bond. However, ethyne is a stronger acid than propyne.
This is attributed to the electron releasing \[+I\] effect of the methyl group
which tends to increase the electron density on the triple bonded carbon atom
in propyne. The release of \[{{H}^{+}}\]ion from propyne is more difficult than
from ethyne or it is a weaker acid than ethyne.
\[\underset{\text{Ethyne}}{\mathop{H-C\equiv
C-H}}\,\,\] \[\underset{\text{Propyne}}{\mathop{C{{H}_{3}}\xrightarrow{{}}-C\equiv
C-H}}\,\]
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