Question

The general formula of alkynes is:
A. \[{C_n}{H_{2n + 2}}\]
B. \[{C_n}{H_{2n}}\]
C. \[{C_n}{H_{2n - 2}}\]
D. \[{C_n}{H_n}\]

Answer 1

Hint: Try to recall that alkynes are acyclic unsaturated hydrocarbons containing carbon-carbon triple bonds .The carbon atoms of a triple bond in alkynes are sp-hybridized. Now, by using this you can easily find the correct option from the given options.

Complete step by step solution:
It is known to you that alkynes are acyclic unsaturated hydrocarbons and the carbon atoms of a triple bond are sp-hybridized. They are linear in shape.
-Alkynes do not show geometrical isomerism because they are linear in shape.
-Also, it is known that propyne is the second member of alkyne series. The chemical formula of ethyne is \[{C_3}{H_4}\].
-Now, since the chemical formula of propyne is known to you and also, it is known that propyne is the second member of alkyne series. So, you can easily find the general formula of alkynes by inspecting each option by putting the value of n =3.
-Option A: On putting the value n=3 in \[{C_n}{H_{2n + 2}}\], we get the chemical formula \[{C_3}{H_8}\]. So, option A is not the correct option and this is the general formula of alkanes.
-Option B: On putting the value n=3 in \[{C_n}{H_{2n}}\], we get the chemical formula \[{C_3}{H_6}\]. So, option B is also an incorrect option and this is the general formula of alkenes.
-Option C: On putting the value n=3 in \[{C_n}{H_{2n - 2}}\], we get the chemical formula \[{C_3}{H_4}\]. So, option C is the correct option and this is the general formula of alkynes.
-Option D: On putting the value n=3 in we get the chemical formula \[{C_3}{H_3}\]. So, option D is also not the correct option.
Hence, from above we can easily say that option C is the correct option to the given question.

Note:
-It should be remembered that terminal alkynes give white precipitate of silver alkyonides on reaction with tollen’s reagent.
-Also, you should remember that like alkenes, alkynes also undergo electrophilic addition reactions.