chemistry lab

[batista_123]

hi guys
I have this lab due tomorrow and I have no idea why my results are not making sense. This is a radical chlorination of 1-chlorobutane, I am sure you have heard of it.
The theoretical percentages of products, according to my calculations, are:
1,1-dichlorobutane 9.50%
1,2-dichlorobutane 38.10%
1,3-dichlorobutane 38.10%
1,4-dichlorobutane 14.30%

ok. we ran a gas chromataography thingy and the teacher posted the results on his website. here is a screenshot.
http://img195.imageshack.us/img195/7962/tiypic.png
By boiling points, I have identified the very left peak as 1,1-dichlorobutane, the one to its right as 1,2, the next one 1,3, and the one to the very right as 1,4.

looking at the second picture, I see that the areas are 3.35, 4.85, 6.07, 11.51
the percentages are
1,1-dichlorobutane 13%
1,2-dichlorobutane 18%
1,3-dichlorobutane 23%
1,4-dichlorobutane 44%
which makes no sense. Then i thought maybe those are not the areas. maybe the areas are 6797.4, 20998.4, 42991.1, 24133.9. but in that case the percentages wont make sense either.

So I am stuck here. This is due tomorrow and I dont see my mistake. can you help me?
god, i hate lab, I would rather take 10 lectures instead of 1 lab.

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[loveoforganic]

If I remember right, gas chrom doesn't work like that. You have a hot block that instantly vaporizes the entire sample - you don't differentially boil individual components into the gas phase. Elution time depends on the interaction with the stationary phase. You'd have to spike the chrom with known samples to positively confirm peak identities.

 

[Astarael]

First of all, your theoretical percentages are off. The chlorine on C1 is electronegative, which means that the transition states for a C2 and C3 radical have different energy associated with them. In this case, I believe the C3 radical (leading to 1,3-dichlorobutane) is more stable, and thus should be slightly higher in abundance than the 1,2 product. I think taking that into account with the fact that you might have flip-flopped two of the compounds (probably what you thought was 1,4 was actually the 1,3 product) and you get something a lot closer to your experimental numbers.

 

[raltima07]

First of all, your theoretical percentages are off. The chlorine on C1 is electronegative, which means that the transition states for a C2 and C3 radical have different energy associated with them. In this case, I believe the C3 radical (leading to 1,3-dichlorobutane) is more stable, and thus should be slightly higher in abundance than the 1,2 product. I think taking that into account with the fact that you might have flip-flopped two of the compounds (probably what you thought was 1,4 was actually the 1,3 product) and you get something a lot closer to your experimental numbers.

+1 this is what I recall