C 4H 8belongs to the homologous series of
alkenes
Identifying the Homologous Series of C4H8
Let's determine which homologous series the organic compound with the molecular formula C4H8 belongs to. Homologous series are a series of compounds with the same general formula, usually differing from each other by a repeating unit, typically a CH2 group. They have similar chemical properties.
To identify the series, we compare the given formula C4H8 with the general formulas of common hydrocarbon homologous series:
- Alkanes: Saturated hydrocarbons with single bonds. General formula is $\text{C}_n\text{H}_{2n+2}$.
- Alkenes: Unsaturated hydrocarbons with at least one carbon-carbon double bond. General formula is $\text{C}_n\text{H}_{2n}$.
- Alkynes: Unsaturated hydrocarbons with at least one carbon-carbon triple bond. General formula is $\text{C}_n\text{H}_{2n-2}$.
For the compound C4H8, the number of carbon atoms is n = 4. Let's substitute n=4 into the general formulas:
- For alkanes: $\text{C}_4\text{H}_{(2 \times 4) + 2} = \text{C}_4\text{H}_{8+2} = \text{C}_4\text{H}_{10}$. This does not match C4H8.
- For alkenes: $\text{C}_4\text{H}_{2 \times 4} = \text{C}_4\text{H}_8$. This matches C4H8.
- For alkynes: $\text{C}_4\text{H}_{(2 \times 4) - 2} = \text{C}_4\text{H}_{8-2} = \text{C}_4\text{H}_6$. This does not match C4H8.
Based on this comparison, the formula C4H8 fits the general formula $\text{C}_n\text{H}_{2n}$, which corresponds to the alkene homologous series. Examples of compounds with the formula C4H8 include but-1-ene, but-2-ene, and 2-methylpropene, all of which are alkenes.
It is worth noting that cycloalkanes also have the general formula $\text{C}_n\text{H}_{2n}$. Cyclobutane and methylcyclopropane have the formula C4H8 and are cycloalkanes. However, amongst the given options, 'alkenes' is the correct homologous series that matches the general formula CnH2n for an open-chain hydrocarbon with this formula.
Let's summarize the general formulas:
| Homologous Series | General Formula |
|---|---|
| Alkanes | $\text{C}_n\text{H}_{2n+2}$ |
| Alkenes | $\text{C}_n\text{H}_{2n}$ |
| Alkynes | $\text{C}_n\text{H}_{2n-2}$ |
| Cycloalkanes | $\text{C}_n\text{H}_{2n}$ |
| Cycloalkenes | $\text{C}_n\text{H}_{2n-2}$ |
Comparing C4H8 with the options, the formula $\text{C}_4\text{H}_8$ matches the general formula $\text{C}_n\text{H}_{2n}$, which is characteristic of alkenes.
Revision Table: Hydrocarbon Homologous Series
| Series | Key Feature | General Formula (n >= 1 or 2) | Example (n=2 or 3) |
|---|---|---|---|
| Alkanes | Single bonds only | $\text{C}_n\text{H}_{2n+2}$ (n >= 1) | Ethane ($\text{C}_2\text{H}_6$) |
| Alkenes | At least one C=C double bond | $\text{C}_n\text{H}_{2n}$ (n >= 2) | Ethene ($\text{C}_2\text{H}_4$) |
| Alkynes | At least one C$\equiv$C triple bond | $\text{C}_n\text{H}_{2n-2}$ (n >= 2) | Ethyne ($\text{C}_2\text{H}_2$) |
| Cycloalkanes | Ring structure, single bonds | $\text{C}_n\text{H}_{2n}$ (n >= 3) | Cyclopropane ($\text{C}_3\text{H}_6$) |
| Cycloalkenes | Ring structure, at least one C=C | $\text{C}_n\text{H}_{2n-2}$ (n >= 3) | Cyclopropene ($\text{C}_3\text{H}_4$) |
Additional Information on Organic Compound Classification
Understanding the general formulas for different homologous series is crucial for classifying organic compounds based on their molecular formula. This classification helps predict their chemical behaviour and properties. Hydrocarbons, which are compounds made only of carbon and hydrogen, are broadly divided into saturated (alkanes) and unsaturated (alkenes and alkynes) compounds, and also into aliphatic (open-chain or non-aromatic cyclic) and aromatic compounds.
Alkenes are more reactive than alkanes due to the presence of the carbon-carbon double bond. This double bond is a site of high electron density and readily undergoes addition reactions.
While C4H8 fits the general formula for both alkenes and cycloalkanes, the options clearly list alkenes, indicating the focus is on the common open-chain homologous series for this formula type.
Important Questions from Hydrocarbons
The number of structural isomers of pentane is
- Refining of petroleum is carried out using which one of the following techniques?
What is the number of mole(s) of H 2(g) required to saturate one mole benzene?
Which one of the following carbon compounds will not give a sooty flame?
Directions: The following 05 (Five) items consist of two statements, Statement I and Statement II. Examine these two statements carefully and select the answers to these items using the code given below:
Statement I: Petroleum is a mixture of many different hydrocarbons of different densities.
Statement II: The grade of petroleum depends mainly on the relative proportion of the different hydrocarbons.
