Question

Which of the following statements is correct for alkyne with the molecular formula ${C_6}{H_{10}}$ ?
(A) It shows structural isomers.
(B) It shows $4$ terminal and $3$ internal alkynes.
(C) It shows $3$ terminal and $4$ internal alkynes.
(D) Only one isomer is chiral.

Answer 1

Alkene and alkynes are unsaturated hydrocarbons containing $C - C$ double and triple bonds respectively. Like alkenes have the suffix – ene, alkynes use the ending –yne. They have a general empirical formula ${C_n}{H_{2n - 2}}$ . They are also known as acetylenes.

Complete answer:
Terminal and internal alkynes: Internal alkynes, the triple bond between carbons are in between the molecules, while for terminal alkynes, the triple bond will be on the terminal end of the molecule. Alkynes are more acidic than the alkanes and alkenes. Internal alkynes feature carbon substituents on each acetylenic carbon. Terminal alkynes have the formula $R{C_2}H$ . Only terminal alkynes have protons. An example is methyl acetylene. Terminal alkynes, like acetylene itself, are mildly acidic, with $p{K_a}$ values of around $25$ .
Terminal alkynes
It shows $7$ structural isomers.
It shows $4$ terminal and $3$ internal alkynes.
Only one isomer is chiral.
So, the correct options are (A) It shows structural isomers, (B) It shows $4$ terminal and $3$ internal alkynes and (D) only one isomer is chiral.

Note:
Internal alkynes, with its $sp$ carbons attached to other carbons, will show weak bands for its triple bond at the $2100 - 2260c{m^{ - 1}}$ region. Terminal alkynes, where the $sp$ carbon is attached to a hydrogen, will show bands on the IR spectrum for both its alkynyl hydrogen and its triple bond.