Question

A molecule of formula C7H12 reacts consecutively as shown below to produce propyl cyclohexane- carboxylate. Identify the structure of the C7H12 molecule and the materials that are produced after each step. Draw only the organic material.

Answer 1

Concepts and reason

The concept used to solve this question is to utilize the functioning of given reagents in the reaction sequence to determine the structure of the unknown compound. The reagent ${\rm{B}}{{\rm{H}}_{\rm{3}}}$ followed by ${{\rm{H}}_{\rm{2}}}{{\rm{O}}_{\rm{2}}}/{\rm{O}}{{\rm{H}}^ - }$ is used in the hydroboration reaction followed by oxidation reaction of an alkene. The reagent ${\rm{Cr}}{{\rm{O}}_{\rm{3}}}/{{\rm{H}}_{\rm{2}}}{\rm{S}}{{\rm{O}}_{\rm{4}}}$ is used in the oxidation of alcohol to carboxylic acid. The reagent LiOH is a base which is used in the deprotonation of carboxylic acid. The reagent bromopropane is used as an alkylating agent.

Fundamentals

Organic chemistry is a branch of chemistry which deals with the synthesis of scaffolds using different reagents by taking specific synthetic route. Every reagent has a specific application which can be used in the synthesis for the functional group transformation. The functional group in the compounds decides the reactivity of the compounds.

The reagent ${\rm{B}}{{\rm{H}}_{\rm{3}}}$ followed by ${{\rm{H}}_{\rm{2}}}{{\rm{O}}_{\rm{2}}}/{\rm{O}}{{\rm{H}}^ - }$ is used in the hydroboration reaction followed by oxidation reaction of an alkene to give an alcohol. Therefore, when this reagent is used the starting material should have an alkene functional group that means the starting material should have at least one double bond.

The reagent ${\rm{Cr}}{{\rm{O}}_{\rm{3}}}/{{\rm{H}}_{\rm{2}}}{\rm{S}}{{\rm{O}}_{\rm{4}}}$ is used in the oxidation of alcohols. Therefore, when this reagent is used the starting material should have an alcohol functional group.

The reagent LiOH is a base which is used in the deprotonation of acidic proton. Therefore, when this reagent is used the starting material should have an acidic proton in it.

The reagent bromopropane is used as an alkylating agent. This reagent can be used in alkylation of an organic compound by following the nucleophilic substitution reaction mechanism.

From the above description of reagents, the following the reaction sequence can be obtained.

From the above scheme, the functional group transformations taken place in the side chain only not on the cyclohexane ring.

The given molecular formula is ${{\rm{C}}_{\rm{7}}}{{\rm{H}}_{{\rm{12}}}}$ .

The double bond equivalence can be calculated as follows:

$\begin{array}{l}\\{\rm{DBE}}\,{\rm{ = }}\,{\rm{C}}\,{\rm{ + }}\,{\rm{1}} - \frac{{{\rm{H}} - {\rm{N}}\,{\rm{ + }}\,{\rm{X}}}}{2}\\\\\,\,\,\,\,\,\,\,\,\,\,\, = \,7 + \,1\, - \frac{{12}}{2}\\\\\,\,\,\,\,\,\,\,\,\,\,\, = \,2\\\end{array}$

The DBE = 2 indicates that the compound may have two double bonds or 1 triple bond or 1 one double bond and a ring.

As in the final compound, the cyclohexane ring is present so the starting material must contain a cyclohexane ring with one double bond.

Also, the reagent used in the first step is ${\rm{B}}{{\rm{H}}_{\rm{3}}}$ followed by ${{\rm{H}}_{\rm{2}}}{{\rm{O}}_{\rm{2}}}/{\rm{O}}{{\rm{H}}^ - }$ which is used in the hydroboration reaction followed by oxidation reaction of an alkene to give an alcohol.

Therefore, it is an alkene.

As in the above mentioned scheme, the functional group transformations taken place in the side chain only so the starting material should contain a terminal double bond which satisfies all the reaction conditions.

From the above points, the expected structure of the starting materail with molecular formula ${{\rm{C}}_{\rm{7}}}{{\rm{H}}_{{\rm{12}}}}$ is as follows:

The structure of the starting material from step 1 is as follows:

When methylenecyclohexane is reacted with ${\rm{B}}{{\rm{H}}_{\rm{3}}}$ followed by ${{\rm{H}}_{\rm{2}}}{{\rm{O}}_{\rm{2}}}/{\rm{O}}{{\rm{H}}^ - }$ undergoes hydroboration followed by oxidation to give primary alcohol as product.

Therefore, the structure of the second compound is as follows:

The structure of the second compound from step 2 is as follows:

When cyclohexylmethanol is reacted with ${\rm{Cr}}{{\rm{O}}_{\rm{3}}}/{{\rm{H}}_{\rm{2}}}{\rm{S}}{{\rm{O}}_{\rm{4}}}$ undergoes oxidation to give carboxylic acid as product.

Therefore, the structure of the third compound is as follows:

The structure of the third compound from step 3 is as follows:

When cyclohexanecarboxylic acid is reacted with LiOH undergoes deprotonation to give lithium salt cyclohexanecarboxylic acid as product.

Therefore, the structure of the fourth compound is as follows:

Ans: Part a

Part a

Answer

The structure of the compound with molecular formula ${{\rm{C}}_{\rm{7}}}{{\rm{H}}_{{\rm{12}}}}$ is as follows:

Answer 2