Class 10 Functional groups, Homologous series, Nomenclature of carbon compounds

Topics to be covered

`=>` Functional groups
`=>` Homologous series
`=>` Nomenclature of carbon compounds


`color{green}(★)` Besides forming bonds with hydrogen, carbon has a tendency to form bonds with other elements like halogens, oxygen, nitrogen and sulphur. In a hydrocarbon chain hydrogen can be raplaced by these elements but the condition is that valency of carbon must be satisfied.

`color{green}(★)` The element replacing hydrogen is referred to as a heteroatom.

`color{green}(★)` The heteroatoms and the group containing these confer specific properties to the compound, regardless of the length and nature of the carbon chain and hence are called functional groups.

Homologous Series

`color{green}(★)` The presence of a functional group dictates the properties of the carbon compound, regardless of the length of the carbon chain. For example, the chemical properties of `color{red}(CH_3OH, C_2H_5OH, C_3H_7OH)` and `color{red}(C_4H_9OH)` are all very similar.

`color{green}(★)` A series of compounds in which the same functional group substitutes for hydrogen in a carbon chain is called a homologous series.
For eg:

`color{green}("𝟏 𝐇𝐨𝐦𝐨𝐥𝐨𝐠𝐨𝐮𝐬 𝐬𝐞𝐫𝐢𝐞𝐬 𝐟𝐨𝐫 𝐚𝐥𝐤𝐚𝐧𝐞𝐬:")`

`color{red}(CH_4)` and `color{red}(C_2H_6)` — these differ by a `color{red}(–CH_2)` – unit

`color{red}(C_2H_6)` and `color{red}(C_3H_8)` — these differ by a `color{red}(–CH_2)` - unit

`color{green}("𝟐 𝐇𝐨𝐦𝐨𝐥𝐨𝐠𝐨𝐮𝐬 𝐬𝐞𝐫𝐢𝐞𝐬 𝐨𝐟 𝐚𝐥𝐤𝐞𝐧𝐞𝐬")`

`color{green}("𝟑 𝐇𝐨𝐦𝐨𝐥𝐨𝐠𝐨𝐮𝐬 𝐬𝐞𝐫𝐢𝐞𝐬 𝐨𝐟 𝐚𝐥𝐤𝐲𝐧𝐞𝐬")`

`color{green}(★)` As the molecular mass increases in any homologous series, a gradation in physical properties is seen because the melting and boiling points increase with increasing molecular mass. Other physical properties such as solubility in a particular solvent also show a similar gradation.

`color{green}(★)` But the chemical properties, which are determined solely by the functional group, remain similar in a homologous series.

Nomenclature of Carbon Compounds

`color{green}(★)` The names of compounds in a homologous series are based on the name of the basic carbon chain modified by a `color{red}("“prefix” “phrase before” or “suffix” “phrase after”")` indicating the nature of the functional group.

𝐍𝐚𝐦𝐢𝐧𝐠 𝐚 𝐜𝐚𝐫𝐛𝐨𝐧 𝐜𝐨𝐦𝐩𝐨𝐮𝐧𝐝 𝐜𝐚𝐧 𝐛𝐞 𝐝𝐨𝐧𝐞 𝐛𝐲 𝐭𝐡𝐞 𝐟𝐨𝐥𝐥𝐨𝐰𝐢𝐧𝐠 𝐦𝐞𝐭𝐡𝐨𝐝 –

(i) Identify the number of carbon atoms in the compound. A compound having three carbon atoms would have the name propane.

(ii) In case a functional group is present, it is indicated in the name of the compound with either a prefix or a suffix (as given in Table 4.4).

(iii) If the name of the functional group is to be given as a suffix, the name of the carbon chain is modified by deleting the final ‘e’ and adding the appropriate suffix. For example, a three-carbon chain with a ketone group would be named in the following manner – Propane `color{red}("– ‘e’ = propan + ‘one’ = propanone.")`

(iv) If the carbon chain is unsaturated, then the final ‘ane’ in the name of the carbon chain is substituted by ‘ene’ or ‘yne’ as given in Table

4.4. For example, a three-carbon chain with a double bond would be called propene and if it has a triple bond, it would be called propyne.