Naming Haloalkanes [Rule Contradiction] (1 Viewer)

[namelyanonymous]

In one of my textbooks, the final rule for naming if there is more than one possible name is:

"The correct name is the one in which the lowest locant is assigned to the functional group cited first as a prefix" i.e. it goes by alphabetical order

In another, the final rule is:

"The correct name is the one that gives the lowest number to the most electronegative halogen"

These contradict in some cases, so I'm unsure which one to go by.

E.g., how would you name:

CH3-CHBr-CH2-CHCl-CH3

If you go by the rule from the first book, then it would be called 2-bromo-4-chloropentane

If you go by the rule in the second book, then it would be called 4-bromo-2-chloropentane (as Cl is more electronegative than Br)

Which one do I use??

Thanks in advance!

 

[nerdasdasd]

In one of my textbooks, the final rule for naming if there is more than one possible name is:

"The correct name is the one in which the lowest locant is assigned to the functional group cited first as a prefix" i.e. it goes by alphabetical order

In another, the final rule is:

"The correct name is the one that gives the lowest number to the most electronegative halogen"

These contradict in some cases, so I'm unsure which one to go by.

E.g., how would you name:

CH3-CHBr-CH2-CHCl-CH3

If you go by the rule from the first book, then it would be called 2-bromo-4-chloropentane

If you go by the rule in the second book, then it would be called 4-bromo-2-chloropentane (as Cl is more electronegative than Br)

Which one do I use??

Thanks in advance!

2-bromo-4-chloropentane

 

[golgo13]

They are like you outlined both correct and arguable in an exam, however like nerdasdasd, has replied it should be 2-bromo-4-chloropentane, because you want the prefix with the highest priority in naming the one alphabetic to have the lowest number in this particular case.
Hope that helps