Q14E - Organic Chemistry (Mcmurry)

Question

Name the following alkynes, and predict the products of their reaction

With:

 (1)  ${\mathbf{H}}_{\mathbf{2}}$in the presence of a Lindlar’s catalyst

 (2)  ${\mathbf{H}}_{\mathbf{3}}{\mathbf{O}}^{\mathbf{+}}$in the presence of ${\mathbf{H}}_{\mathbf{2}}{\mathbf{SO}}_{\mathbf{4}}$

Step-by-Step Solution

Answer

1. The IUPAC name of the structure given is 3,3-Dimethylhex-1-yne. The product formed when 3,3-Dimethylhex-1 yne reacts with  ${\mathrm{H}}_2$ in presence of Lindlar’s catalyst is 3,3-Dimethylhex-1-ene. The product formed on reaction with  ${\mathrm{H}}_3{\mathrm{O}}^{+}$ in presence of ${\mathrm{H}}_2{\mathrm{SO}}_4$  is 3,3-Dimethyl-hexan-2-one.
2.  The IUPAC name of the structure given is 2,7-Dimethyloct-4-yne. The product   formed when 2,7-Dimethyloct-4-yne reacts with   in presence of Lindlar’s catalyst is cis 2,7-Dimethyloct-4-ene. The product formed on reaction with   ${\mathrm{H}}_3{\mathrm{O}}^{+}$ in presence of ${\mathrm{H}}_2{\mathrm{SO}}_4$  is 2,7-Dimethyloctan-4-one.

Definition of alkynes

Molecular compounds containing triple bonds are referred to as alkynes

Structure and naming

Black sphere represent - carbon

Grey sphere represent – hydrogen

The spheres are substituted by the respective atoms to get the structural formula. Then the compound is named following the rules of IUPAC nomenclature. The IUPAC name of the given compound is 3,3-Dimethyl-hexan-2-one.

Reaction with H 2 in presence of Lindlar’s catalyst

In the presence of Lindlar’s catalyst one hydrogen molecule is added across the triple bond. In this reaction the alkyne is reduced to alkene.   3,3-dimethylhex-1-yne  is reduced to 3,3-dimethylhex-1-ene in presence of Lindlar’s catalyst.

Reaction with H 3 O + in the presence of H 2 SO 4

In acidic medium, the alkyne is converted to a ketone. Thus, 3,3-dimethylhex-1-yne is converted to 3,3-dimethylhexan-2-one.

Structure and naming

Black sphere represent - carbon

Grey sphere represent – hydrogen

The spheres are substituted by the respective atoms to get the structural formula. Then the compound is named following the rules of IUPAC nomenclature. The IUPAC name of the given compound is 3,3-Dimethyl-hexan-2-one.

Reaction with H 2 in presence of Lindlar’s catalyst

In the presence of Lindlar’s catalyst one hydrogen molecule is added across the triple bond. In this reaction the alkyne is reduced to alkene.   2,7-dimethyloct-4-yne  is reduced to cis 2,7-dimethyloct-4-ene in presence of Lindlar’s catalyst.

Reaction with H 3 O + in the presence of H 2 SO 4

In acidic medium, the alkyne is converted to a ketone. Thus, 2,7-dimethyloct-1-yne is converted to 2,7-dimethyloctan-2-one.