Q55 E - Organic Chemistry (Mcmurry)

Question

There are two different substances with the formula C₂H₆O. Draw both, and tell how they differ.

Step-by-Step Solution

Answer

   ${\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{OH}$                                         ${\mathrm{CH}}_3{\mathrm{OCH}}_3$

The two compounds differ in the location of oxygen atom. This both compound are example of a Functional group isomerism in which compound have same molecular formula but different functional group.

Structural Isomerism

Structural isomers are those isomers in which the atoms are completely arranged in a different order with the same molecular formulas. These are the molecules having the same kind of molecular formula with different connectivities depending upon the order they are put together.

The structural isomerism is also called as constitutional isomerism as per the IUPAC. It is a kind of isomerism where the molecule have the same molecular formula with different orders and bonding, as opposed to that of stereoisomerism.

Types of structural isomerism

There are three types of structural isomerism

Chain Isomerism- Chain isomerism occurs when there is difference in the atomic arrangement of the carbon to carbon chain of molecule. This phenomena is also called as skeletal isomerism. Example butane and 2-methyl propane.

Position Isomerism- positional isomerism arises when there is difference in the position occupied by substituent atom or group of the atoms or due to unsaturation occurring in chain.

Functional Group Isomerism- The functional group isomerism occurs when there is a presence of the odd form of functional group with same molecular formula. For example dimethyl ether and ethanol have same molecular formula C₂H₆O but different functional groups.

Differ two compounds which having same molecular formula C 2 H 6 O by structural isomerism (functional group Isomerism).

A.  ${\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{OH}$                           B. ${\mathrm{CH}}_3{\mathrm{OCH}}_3$

Ethyl alcohol                              Dimethyl ether

 

Sometime there is more than one way to connect a given group of atoms into a molecular structure. They have the same molecular formula but different structures which give them their unique properties. These two compounds are functional isomers. At room temperature dimethyl ether is gas whereas ethanol is liquid.

 The functional group of A is alcohol.

The functional group of B is ether.