Identify the functional group, list the first three members of the homologous series and draw the structure of but-1-yne. Explain the distinction between an alkene and alcohol using bromine water. Des

a)

(iii) The functional group $-C\equiv C-$ represents an alkyne. The first member is ethyne ($\text{C}_2\text{H}_2$), the second is propyne ($\text{C}_3\text{H}_4$). The third member is butyne ($\text{C}_4\text{H}_6$). A possible structure for butyne is but-1-yne:

$$\text{CH}_3\text{CH}_2\text{C}\equiv\text{CH}$$

(iv) Compound D (alcohol) can be distinguished from compound B (alkene) using bromine water.

• When bromine water (orange-brown) is added to compound B (alkene), it will be decolorized as the bromine adds across the double bond.
• When bromine water is added to compound D (alcohol), there will be no observable change (it remains orange-brown).

(v)

• For the functional group $-C-C-$ (saturated carbon-carbon bond, as in alkanes), the reaction with a bromine molecule is Substitution.
• For the functional group $-C=C-$ (carbon-carbon double bond, as in alkenes), the reaction with a bromine molecule is Addition.