chemistry

i need and answer

I'm not sure I understand what you are asking.

The compound you have written is chloro-pentane. Normal pentane is C5H12. In your compound one of the hydrogen atoms has been replaced with a chlorine atom. I am assuming at least part of your problem is in specifying the location of the chlorine atom.

If I remember freshman chemistry correctly, you number the carbon atoms from one to five from left to right. If the chlorine atom is bonded to the first carbon atom, then your compound is "1- chloropentane". For the second carbon atom it would be "2-chloropentane", and for the third carbon atom it would be "3-chloropentane". In this case, there would be no difference between 2 and 4-Chloropentane and between 1 and 5 chloropentane.

There is also a consideration when the arrangements can be mirror images of each other. In that case we would also add an alpha-prefex to tell which type (left or right) the isomer would be, but I do not believe that applies here.

In short, I see three possible isomers of chloro-pentane:

1. "1-chloropentane" which is either:

H H H H H
| | | | |
Cl-C-C-C-C-C-H
| | | | |
H H H H H

or

H H H H H
| | | | |
H-C-C-C-C-C-Cl
| | | | |
H H H H H

2. "2-chloropentane", which is either:


H Cl H H H
| | | | |
H-C-C-C-C-C-H
| | | | |
H H H H H

or

H H H Cl H
| | | | |
H-C-C-C-C-C-H
| | | | |
H H H H H

3. And 3-Chloropentane:


H H Cl H H
| | | | |
H-C-C-C-C-C-H
| | | | |
H H H H H

Since you mentioned seven isomers, I suppose your instructor may want the chlorines in the other positions on each carbon atom, such as:

H H H H H
| | | | |
H-C-C-C-C-C-H
| | | | |
Cl H H H H

for "1-chloropentane". If this is the case, then there are 12 isomers, but still only three ways of writing it.

What I've written are the IUPAC (International Union of Pure and Applied Chemists) nomenclature from freshman chemistry in 1974. It's possible I'm not up on the latest nomenclature conventions. You may wish to do an internet search on "isomers" to come up with what's current.

You can also branch the pentane--e.g.
(CH3)2-CH-CH2-CH2Cl

etc (with the chlorine @ various positions)

or

(CH3)3-C-CH2Cl