Question

Which of the following statements is not correctly showing the trend of the properties mentioned ?

• A. $C{H}_{3}C{H}_{2}OH>C{H}_{3}C{H}_{2}C{H}_{2}OH>\underset{\left(Solubility\right)}{C{H}_{3}C{H}_{2}C{H}_{2}C{H}_{2}OH}$
• B. $C{H}_{3}C{H}_{2}OH>C{H}_{3}C{H}_{2}C{H}_{2}OH>\underset{\left(Boilingpoint\right)}{C{H}_{3}C{H}_{2}C{H}_{2}C{H}_{2}OH}$
• C. $C{H}_{3}C{H}_{2}C{H}_{2}OH>C{H}_3\underset{C{H}_3}{\underset{|}{CH}}-C{H}_{2}OH>\underset{Boilingpoint}{C{H}_3-\underset{C{H}_3}{\underset{|}{\stackrel{C{H}_3}{\stackrel{|}{C}}}}-OH}$
• D. $C{H}_3-\underset{C{H}_3}{\underset{|}{\stackrel{C{H}_3}{\stackrel{|}{C}}}}-OH$<$C{H}_3\underset{C{H}_3}{\underset{|}{CH}}-C{H}_{2}OH$ <$C{H}_{3}C{H}_{2}C{H}_C{H}_{2}OH$

Answer 1

Answer: (D)

$C{H}_3-\underset{C{H}_3}{\underset{|}{\stackrel{C{H}_3}{\stackrel{|}{C}}}}-OH$<$C{H}_3\underset{C{H}_3}{\underset{|}{CH}}-C{H}_{2}OH$ <$C{H}_{3}C{H}_{2}C{H}_C{H}_{2}OH$

Boiling point and solubility of alcohols is determined by the ease and extent of H-bonding among the alcohol molecules. More is the hydrogen bonding higher is the boiling point and solubility in water. Thus, tertiary alcohols being highly hindered will have least hydrogen bonding and thus low boiling point/solubility as compared to less hindered secondary alcohol.

Therefore the order of boiling point is primary alcohol>secondary alcohol>tertiary alcohol as:

$C{H}_{3}C{H}_{2}C{H}_{2}OH>C{H}_{3}CH\left(C{H}_3\right)C{H}_{2}OH>C{H}_{3}C(C{H}_3{)}_{2}OH$

In case of linear versus branched alcohol, linear alcohol has higher melting/boiling points due to better stacking and surface area contact.

But in case of highly branched vs. branched molecules more sphere-like structure of the molecule better is the stacking thus higher will be the melting point. Thus order of melting point will be

$C{H}_{3}CH\left(C{H}_3\right)C{H}_{2}OH<C{H}_{3}C(C{H}_3{)}_{2}OH<C{H}_{3}C{H}_{2}C{H}_{2}C{H}_{2}OH$

A and B. Solubility and boiling point of alcohols depends on the chain length. Longer is the chain length, lesser is the solubility/boiling point as the extent of H-bonding decreases. Also, the hydrophobic nature of the hydrocarbon chain reduces the solubility.

thus order of solubility and boiling point will be:

$C{H}_{3}C{H}_{2}OH>C{H}_{3}C{H}_{2}C{H}_{2}OH>C{H}_{3}C{H}_{2}C{H}_{2}C{H}_{2}OH$