TBR Hydrocarbon Chapter Passage I

[Jay2910]

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Hey Everyone,

Is it just me or does this explanation look like it has something wrong with it? Why is the center carbon lacking protons? Is that center carbon by chance a tertiary? Or did they not care to put those in because of stereochemistry?

I am having problems with question 5 on Passage I of the Hydrocarbon reactions Chapter btw.

The link is below:
http://i1072.photobucket.com/albums/w371/Goldeolde/IMAG0212.jpg

Thanks!

 

[BB8730]

What is the question asking? It looks like they just omitted them because they were irrelevant to the question.

 

[Jay2910]

The Question asks:
Following the free radical monochlorination of pentane, what is the ratio of 2-chloropentane to 1-chloropentane?

A) 2:3
B) 5:3
C) 2.5: 1
D) 3:1

I thought the answer is C but I didn't take into account the number of hydrogens. I get how they took the ratio number( 1) and multiplied it by "6 possible hydrogens" that Chlorine can replace.
I don't get how they got the 4 . .. I thought it was 6 possible secondary hydrogens . . ..

Can someone please clarify?

 

[BB8730]

I don't get how they got the 4 . .. I thought it was 6 possible secondary hydrogens . . ..

There are only 4 hydrogens that could lead to 2-chloropentane. The two in the middle don't matter (which is probably why they didn't include them in the solution) because they would lead to 3-chloropentane.

 

[shamwowzer]

The Question asks:
Following the free radical monochlorination of pentane, what is the ratio of 2-chloropentane to 1-chloropentane?

A) 2:3
B) 5:3
C) 2.5: 1
D) 3:1

I thought the answer is C but I didn't take into account the number of hydrogens. I get how they took the ratio number( 1) and multiplied it by "6 possible hydrogens" that Chlorine can replace.
I don't get how they got the 4 . .. I thought it was 6 possible secondary hydrogens . . ..

Can someone please clarify?

It wouldn't be 2-chloro pentane if it attached to the middle carbon...

Sent from my DROID2 using Tapatalk

 

[indianjatt]

I find this question very vague. Do they mean how many different hydrogens can the chlorine attack to form each product or are they talking about Product distribution ratios..... If the latter, none of the answer choices would be correct. Anyone willing to clarify?

 

[CodeRedDew]

I find this question very vague. Do they mean how many different hydrogens can the chlorine attack to form each product or are they talking about Product distribution ratios..... If the latter, none of the answer choices would be correct. Anyone willing to clarify?

It's talking about product distribution ratios. I'm assuming TBR gives you the fact that secondary carbon radicals are 2.5x easier to form than primary carbon radicals; therefore, since there are 4 hydrogens on secondary carbons, you must multiply that number by 2.5 (since it takes the extraction of a hydrogen to form a radical). Then by doing so, you compare that number, which is 10, to the number of hydrogens on the primary carbons. Hence the ratio is 10:6 or 5:3.

 

[Hanguk]

Was the 2.5x thing mentioned in the passage? Because if so you have sufficient knowledge to solve the question.