Chemical Forums

Chemistry Forums for Students => High School Chemistry Forum => Topic started by: patrisha_boo on March 30, 2005, 12:29:30 AM

Title: 18 different isomers of octane (c8h18)
Post by: patrisha_boo on March 30, 2005, 12:29:30 AM
1)
   h h h h h h h h
h-c-c-c-c-c-c-c-c-h
   h h h h h h h h

2)
   h h h h h h   h    h
h-c-c-c-c-c-c -  c-    c-h
  h h h h h h   h  h-c-h
                           h
3)
   h h h h h h
h-c-c-c-c-c-c-h
   h h h h hch-hch
                h    h
4)
   h h h h h  
h-c-c-c-c-c-h
   h h hch hch-hch
          h    h    h
5)
   h    h    h    h
h-c-   c-   c-    c  -h
  hch hch hch hch
    h    h    h    h

I don't really know how to find the other 13 isomers.
Title: Re:18 different isomers of octane (c8h18)
Post by: AWK on March 30, 2005, 04:17:32 AM
It should be 18. Try to name all these isomers.
Title: Re:18 different isomers of octane (c8h18)
Post by: Octane on May 19, 2005, 08:41:41 PM
n-octane

2-methylheptane
 3-methylheptane
4-methylheptane

2,2-dimethylhexane
2,3-dimethylhexane
2,4-dimethylhexane
2,5-dimethylhexane
3,3-dimethylhexane
3,4-dimethylhexane
3-ethylhexane

2,2,3-trimethylpentane
2,2,4-trimethylpentane
2,3,3-trimethylpentane
2,3,4-trimethylpentane
3-ethyl-2-methylpentane
3-ehtyl-3-methylpentane
 
2,2,3,3-tetramethylbutane

I belive that that is all, I have rechecked them several times and no doubling, there is 18 of them too.
Title: Re:18 different isomers of octane (c8h18)
Post by: Donaldson Tan on May 20, 2005, 12:24:49 AM
gosh.. 900++ views for this post.. LOL
Title: Re:18 different isomers of octane (c8h18)
Post by: Communique on May 28, 2005, 01:11:44 PM
Quote from: Octane on May 19, 2005, 08:41:41 PM
2,3,4-trimethylpentane
3-ethyl-2-methylpentane
3-ehtyl-3-methylpentane

Wouldnt it be
3,3,4-trimethylpentane
2-methyl-3-ethylpentane
3-methyl-3-ethylpentane

The last two I think are the same as what you have posted, just named a little differently. As a lab in chem class were supposed to name and draw out all the isomers of octane and my question is, would a difference in naming like that matter at all? Because they are really the same thing I think...
Title: Re:18 different isomers of octane (c8h18)
Post by: janne18 on May 29, 2005, 05:31:53 AM
Quote from: Communique on May 28, 2005, 01:11:44 PM
Wouldnt it be
3,3,4-trimethylpentane
2-methyl-3-ethylpentane
3-methyl-3-ethylpentane

The last two I think are the same as what you have posted, just named a little differently. As a lab in chem class were supposed to name and draw out all the isomers of octane and my question is, would a difference in naming like that matter at all? Because they are really the same thing I think...

Nope. I agree with Octane. Remember that substituents are supposed to have the lowest possible numbers and that the substituents should be in alfabetic order. ethyl before methyl :)
Title: Re:18 different isomers of octane (c8h18)
Post by: AWK on May 30, 2005, 01:34:46 AM
Octane did some errors.
the proper name of all isomers are (left to right, up to down  - see my scheme):
n-octane,  2-methylheptane, 3-..., 4-...,
2,2-dimethylhexane, 2,3-..., 2,4-..., 2,5-...,
3,3-dimethylhexane, 3,4-..., 3-ethylhexane,
2,2,3-trimethylpentane, 2,2,4-..., 2,3,3-..., 2,3,4-...,  3-ethyl-2-methylpentane,
3-ethyl-3-methylpentane,
2,2,3,3,-tetramethylbutane.
Title: Re:18 different isomers of octane (c8h18)
Post by: woelen on May 30, 2005, 03:45:26 AM
Quote from: AWK on March 30, 2005, 04:17:32 AM
It should be 18. Try to name all these isomers.
Wow... you did your homework very well.

Just to tease you with this puzzle on alkanes.... ;D
What is the generic mathematical expression of the number of isomers of CnH2n+2?
Give the number of isomers as an integer function of n.

Below follows the value of this function for some small values of n.

1 1
2 1
3 1
4 2
5 3
6 5
7 9
8 18
9 35
10 75
12 355
15 4347



Wilco
Title: Re:18 different isomers of octane (c8h18)
Post by: AWK on May 30, 2005, 07:14:36 AM
http://www.scctm.org/Awards/Ballard_Paper.pdf