Question

Which of the following compounds is an example of a homologous series of alcohols?
$\begin{align}
  & a)C{{H}_{3}}OH \\
 & b)C{{H}_{3}}C{{H}_{2}}OH \\
 & c)C{{H}_{3}}C{{H}_{2}}C{{H}_{2}}OH \\
 & d)All\text{ }of\text{ }the\text{ }above \\
\end{align}$

Answer 1

Hint: Homologous series is a sequence of compounds with the same functional group and similar chemical properties. Try keeping this in mind when picking an answer.

Step-by-Step Solution:
Let us analyse what a homologous series really is before we come up with an answer.
In the field of organic chemistry, a homologous series is a sequence of compounds with the same functional group and similar chemical properties in which the members of the series can be branched or unbranched. This can be the length of a carbon chain, for example in the straight-chained alkanes (paraffins), or it could be the number of monomers in a homopolymer such as amylose.
Compounds within a homologous series typically have a fixed set of functional groups that gives them similar chemical and physical properties. (For example, the series of primary straight-chained alcohols has a hydroxyl at the end of the carbon chain.) These properties typically change gradually along the series, and the changes can often be explained by mere differences in molecular size and mass.
Let us now look at what a homologous series of alcohols could look like.
The alcohols which only contain one hydroxyl group attached to a saturated carbon form a homologous series.
A hydrocarbon homologous series is a series of hydrocarbons which:
Have the same general formula
Differ by CH2 in molecular formulae from neighbouring compounds
Show a gradual variation in physical properties i.e. boiling and melting point
Have similar chemical properties
The general formula for the homologous series of alcohols is:
\[{{C}_{n}}{{H}_{\left( 2n+1 \right)}}OH\]
Using this general formula of homologous series of straight chain alcohols, we see that all of the given options fit the criteria. Therefore, the answer to this question can be concluded to be d).

Note: The concept of homologous series was proposed in 1843 by the French chemist Charles Gerhardt. A homologation reaction is a chemical process that converts one member of a homologous series to the next member.