Question

Which of the following is (are) member of same homologous series? (A) \(\mathrm{CH}_{3}-\mathrm{OH}, \mathrm{CH}_{3}-\mathrm{O}-\mathrm{CH}_{3}, \mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{CH}_{2}-\mathrm{OH}\) (B) \(\mathrm{CH}_{3}-\mathrm{COOH} \cdot \mathrm{CH}_{3}-\mathrm{COOCH}_{3}, \mathrm{CH}_{3}-\mathrm{CO}-\mathrm{CH}_{2}-\mathrm{CH}_{2}-\mathrm{OH}\) (C) \(\mathrm{C}_{3} \mathrm{H}_{2} \mathrm{Cl}, \mathrm{C}_{5} \mathrm{H}_{11} \mathrm{Cl}, \mathrm{C}_{7} \mathrm{H}_{15} \mathrm{Cl}\) (D) \(\mathrm{H}_{2} \mathrm{O}, \mathrm{CH}_{3}-\mathrm{OH} \cdot \mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{OH}\)

Short answer

The answer is (C) and (D). The compounds in these options follow the general formulas \(\mathrm{C_{n}H_{2n+1}Cl}\) (alkyl halide series) and \(\mathrm{C_{n}H_{2n+2}O}\) (alcohol series), respectively, indicating that they belong to the same homologous series.

Step-by-step solution

Identify the general formula of each homologous series

Here, we need to derive a general formula for each homologous series that represents the constant unit difference between each member's molecular mass. (A) The compounds have the following functional groups: alcohol, ether, and alkane with an alcohol group. There is no consistent pattern. (B) The compounds have the following functional groups: carboxylic acid, ester, and ketone with an alcohol group. There is no consistent pattern. (C) The compounds have the following general formula: \(\mathrm{C_{n}H_{2n+1}Cl}\), which represents the alkyl halide homologous series. Here, n refers to the number of carbon atoms. (D) The compounds have the following general formula: \(\mathrm{C_{n}H_{2n+2}O}\) which represents the alcohol homologous series. Here, n refers to the number of carbon atoms.

Determine the option with the same homologous series

From our analysis in Step 1, options (C) and (D) both follow a general formula, corresponding to the alkyl halide and alcohol homologous series, respectively. Thus, the compounds in options (C) and (D) are members of the same homologous series. Therefore, the answer is (C) and (D).

Key concepts

Understanding Organic Chemistry

Organic chemistry is a fascinating and extensive field of chemistry that deals with carbon-containing compounds. Known for their vast diversity, these compounds form the basis of life and are central to modern industry and medicine. Interestingly, carbon atoms have the unique ability to bond with each other in long chains and rings, which gives rise to an incredible variety of structures.

Within organic chemistry, scientists study the properties, reactions, and synthesis of organic molecules. A fundamental concept within this field is the ability to identify patterns in molecular structures. This leads us to homologous series—groups of organic compounds that have similar chemical properties and differ by a constant unit, usually a '-CH2-' group. These series demonstrate how slight changes in structure can lead to compounds with related, yet distinct, properties.

Understanding the structural differences and similarities within homologous series is crucial for predicting the behavior of organic compounds in various chemical reactions.

Functional Groups: The Chemical Reactivity Signposts

Functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. Think of them as distinct 'functional' areas in an organic compound. These groups define how a molecule will interact with other substances and are key to understanding organic chemistry.

Common functional groups include alcohols (with an -OH group), carboxylic acids (with a -COOH group), and alkyl halides (with a -X, where X is a halogen atom). By identifying the functional groups present in a molecule, chemists can predict the molecule's physical and chemical properties, such as solubility and acidity.

It's important for students to become familiar with these functional groups, as they are the foundational concepts that allow us to classify organic compounds, understand their reactivity, and navigate through the vast landscape of organic chemistry.

Alkyl Halides: Understanding their Role and Reactivity

Alkyl halides are a type of organic compound where a halogen (such as fluorine, chlorine, bromine, or iodine) is bonded to an alkyl group (a carbon chain). These compounds are well-known for their interesting reactivity and are commonly used in various chemical reactions, like nucleophilic substitutions or elimination reactions.

In the context of homologous series, alkyl halides have a general formula of \( \mathrm{C_{n}H_{2n+1}X} \), where 'X' represents a halogen atom. They form a series where each successive compound differs by a '-CH2-' unit from the previous one. This pattern provides a predictable change in physical properties, such as boiling points, as the carbon chain increases while maintaining similar chemical reactivity—making them an excellent case study for understanding the behavior of homologous series in organic chemistry.

Alcohols: Versatile Hydroxyl-bearing Compounds

Alcohols are organic compounds where one or more hydrogen atoms in an alkane are replaced by a hydroxyl (-OH) group. Their general formula is \( \mathrm{C_{n}H_{2n+2}O} \) for the simplest alcohols where only one hydroxyl group is present. As one of the most common functional groups, alcohols play a vital role in organic chemistry and can be found in various forms ranging from simple molecules like methanol (\( CH3OH \)) to complex structures such as steroids.

The presence of the hydroxyl group makes alcohols polar, which affects their boiling points and solubility in water. Alcohols can engage in hydrogen bonding, making them more water-soluble than their hydrocarbon counterparts. Moreover, alcohols can be classified into primary, secondary, and tertiary types, based on the number of carbon atoms connected to the hydroxyl-bearing carbon—another fine example of classifying organic compounds based on their structural characteristics.