Question

1. What is an isomer? How many possible isomers of hexane are there? What are the structural differences between these isomers? Answer: Type your answer here. (Score for Question 2: ___ of 6 points) 2. Look at page 54 in your Laboratory Guide. Note that butane has two possible isomers but that decane has 75 possible isomers. Why does the number of possible isomers go up with an increasing number of carbon atoms? Answer: Type your answer here. (Score for Question 3: ___ of 7 points) 3. Look at the table of boiling points on page 54 of your Laboratory Guide. These are the boiling points for the unbranched hydrocarbons listed. Consider your models and, drawing on your knowledge of bonding and chemical forces, infer what might contribute to the increasing boiling points as the carbon chains grow longer. Then state whether you think all of the isomers of a compound have the same or different boiling points; give a reason for your answer. Answer: Type your answer here.

Answer 1

Answer 1:
Isomers are compounds with same molecular formula but different structure formula. Isomers are classified into two types
a) Structural/configurational isomers
b) Stereo isomers
In structural/configurational isomers  atom and functional groups are attached in different fashion. Structural isomers may have different functional groups. Structural isomers are further classified as chain isomers, position isomers and functional isomers. In case of stereo-isomers, compounds have same functional group, but different orientation in space. They also have difference activity towards polarized light.

 Answer 2:
Hexane has a molecular formula of C6H14. It exhibits following structural isomers
a) hexane,
b) 2-methylpentane
c)3-methylpentane
d) 2,2-dimethylbutane
e) 2,3-dimethylbutane
Thus, in all there are 5 isomers of hexane

Answer 3: 
Butane has two possible isomers but that decane has 75 possible isomers. This can be attributed to the fact that butane has 4 carbon atoms, while decane has 10 carbon atom. As the number of carbon atom increases, there are higher possible sites of linkage, in different fashion. Therefore, as number 69 of carbon atoms increases, number of different possible isomers increases. 

Answer 4:
It has been observed that, though isomers have same molecular formula, but the have different boiling points. Infact, branched isomers have lower boiling point as compared to linear isomers. For example, hexane has boiling point = 69 oC, 2 methyl pentane has boiling point = 60 oC, 2,4, dimethyl butane has boiling point = 58 oC and 2,2 dimethyl butane has boiling point = 50 oC. Thus, it can be observed that branched isomers have lower boiling points as compared to linear isomers. This can be attributed to lower van der Waal's forces of interaction in branched isomers as compared to linear isomers.