Q56 E - Organic Chemistry (Mcmurry)

Question

There are three different substances that contain a carbon–carbon double bond and have the formula C₄H₈. Draw them, and tell how they differ.

Step-by-Step Solution

Answer

The three substances that contain a carbon-carbon double bond and have the formula${\mathrm{C}}_4{\mathrm{H}}_8$ are

 

$C{H}_{3}C{H}_{2}CH=C{H}_2$    $C{H}_{3}CH=CHC{H}_3$ 

The compound differ in the location of double bond and the way that carbon atoms are connected with each other.

Isomers

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 connectivity’s 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.

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 4 H 8 by structural isomerism (Position Isomerism).

Due to difference in the unsaturation of the molecule they show different chemical properties despite there molecule formula is same i.e. ${\mathrm{C}}_4{\mathrm{H}}_8$ .

      $C{H}_{3}C{H}_{2}CH=C{H}_2$      $C{H}_{3}CH=CHC{H}_3$                                                                                      

                                                                                                  

        A.1-butene                          B. 2-butene                         C. 2-methyl-1-propene

 

These structural difference is explained by the concept of Positional Isomerism in which there is difference in the position occupied by substituent atom or group of the atoms or due to unsaturation occurring in chain.

Here, the compounds show difference in the structure of double bond. So, we can differ all three compounds despite of having same molecular formula.