Question

Comment on alkynes preparation and chemical properties of alkyne.

Answer 1

$i.$ An alkyne may be prepared by heating a dehaloalkane with alcoholic $KOH$.

$R-\underset{X}{\underset{|}{\stackrel{X}{\stackrel{|}{CH}}}}-\underset{X}{\underset{|}{C{H}_2}}+2KOH⟶R-C\equiv CH+2KX+2H_{2}O$

$ii.$ Vicinal tetrahaloalkanes can be dehalogenatedwith $Zn$ metal in an organometallic reaction to form alkynes.

$R-\underset{X}{\underset{|}{\stackrel{X}{\stackrel{|}{C}}}}-\underset{X}{\underset{|}{\stackrel{X}{\stackrel{|}{C}}}}-R+Zn⟶R-C\equiv C-R+Zn{X}_2$

$\underset{–}{Chemicalproperties}$

$1.$ The $H$ atoms attached to triply bonded carbon atoms are acidic in nature.

$2.$ Alkynes undergo electrophilic addition reactions.

See the given structure.

$3.$ Alkynes undergo polymerisation under suitable conditions.