a. Give the structure of lowest molecular mass and optically active alkyne.
b. Give the structure of unsaturated hydrocarbon with lowest molecular mass showing diastereomers.
c. Give the structure of alkyne that gives the same product on reaction with either `H_2+Ni_2B` or `K+C_2H_5OH`.
d. Give the structure of alkyne that gives the same single product on reaction with either `(B_2H_6//THF+H_2O_2//overset(Ө)H)` or dil. `H_2SO_4//Hg^(2+)//H^(o+)`.
e. Give the structure of alkyne that gives the same two products with either of the reagents in (d).

Explanation

a. For an alkyne to be optically active, four different groups should be attached to the C atom. To have the lowest molecular mass, the four groups should be:
(1) H (2) `HC-=C-` (3) Me (4) Et-
The structure is:

b. To show diastereomers, there must be one double bond of the type
To posses the lowest molecular mass, R should be alkyne.
The structure is:

c. Since the reaction of alkyne with `H_2+Ni_2B` is syn-addition and that with `(K+C_2H_3OH)` is anti-addition of two H atoms, it would give `c//s` and `trans` stereoisomers. To avoid this the alkyne must be terminal.
The structure is:
d. Since the HBO reaction is anti-Markovnikov's and catalytic hydration of alkyne is Markovnikov's to give the same single product, the alkyne must be of symmetrical and internal type.
The structure is

e. To get two different products, teh alkyne must be of unsymmetrical and internal type.
The structure is: