Question 4 Page 69 (ii) - Chapter 4 Class 10 - Carbon and its Compounds

Draw the structures for the following compounds.

(ii) Bromopentane*

*Are structural isomers possible for bromopentane?

Answer:

Bromopentane is Bromine (Bromo-) atom attached to a 5 carbon( -pent) compound with single bonded ( -ane ) carbon atoms. 

It has a Bromine atom connected to it at one end.  

Yes, bromopentane has several structural isomers:

  STEP 1

The simplest 5 carbon compound we can draw is by placing all five in a straight line. 

• So first, we will place 5 carbon atoms in a straight line , and place the H atoms in a way that satisfies their valency. This structure is known as n-pentane.
• To this we will add the Br atom at one end, to make bromopentane.
• Moving around this Br atom to different positions, we can get 3 distinct compounds that have the same chemical formula. These compounds, namely, 1-Bromopentane, 2-Bromopentane, 3-Bromopentane, are isomers of Bromopentane. 

STEP 2  

Further, more structural isomers can be found by moving the carbon atoms on the end to make a branching structure.

• Moving 1 carbon atom so as to form one branch and placing H-atoms to satisfy valency forms a structure known as Isoprene .
• The Br atom can be placed in different positions to obtain 3 distinct structures , namely 1-bromo-3-methylbutane , 2-bromo-3-methylbutane , 2-bromo-2-methylbutane. These are also structural isomers of bromopentane as they have the same formula.

STEP 3

Now, we repeat the above step, to form Neopentane and place a Br atom in different positions to form distinct structures that will also be structural isomers to bromopentane.

We cannot move the Br atom or the methyl group anywhere to form any more distinct structures.

Hence, Bromopentane has 7 structural isomers .