Question

Two successive compounds, having same functional group. They have a difference of :

• A. -CH$_2$ Unit
• B. -CH$_3$ Unit
• C. -C$_2$H$_2$ Unit
• D. -CH$_4$ Unit

Hint:

Remember that a homologous series is characterized by compounds having the same functional group and differing by a -CH$_2$ unit. This difference leads to a predictable change in molecular mass (14 amu) and a gradual change in physical properties.

Answer 1

The Correct Option is A

Step 1: Understand the concept of homologous series.
In organic chemistry, a homologous series is a series of compounds with the same general formula, usually varying by a single parameter such as the length of a carbon chain. All compounds in a homologous series have the same functional group and similar chemical properties, with a gradual change in physical properties as the series progresses. Step 2: Identify the difference between successive members of a homologous series.
Successive compounds in a homologous series differ by a -CH$_2$ (methylene) unit. For example, in the alkane series:
Methane (CH$_4$)
Ethane (C$_2$H$_6$) - differs from methane by one -CH$_2$ group (CH$_4$ + CH$_2$ = C$_2$H$_6$)
Propane (C$_3$H$_8$) - differs from ethane by one -CH$_2$ group (C$_2$H$_6$ + CH$_2$ = C$_3$H$_8$) This pattern holds true for other homologous series as well (e.g., alcohols, carboxylic acids, etc.), as long as they have the same functional group. Step 3: Compare the conclusion with the given options.
The difference between two successive compounds having the same functional group is a -CH$_2$ unit. This corresponds to option (1). $$(1) -CH$_2$ Unit$$