[ish]

Here's the problem:
.50000g 1,3-dimethylcyclohexane reacts with chlorine to give mono-chlorinated products.  All the dimethylcyclohexane is used up.  Relative rates of reactivity for tertiary, secondary and primary hydrogens under free radical chlorination conditions are 5.0, 3.6 and 1.0 respectively.  Ignoring stereoisomers calculate the number of grams of each unique mono-chlorinated product.  Show work.

So here's my take:6 total primary Hydrogens, 8 secondary and 2 tertiary.  With the rates given that means the ratio is primary: 1*6=6,  secondary: 3.6*8=28.8 tertiary: 5*2=10.  As far as determining amount of product, percentage-wise that gives me primary: 6/44.8= 13.4%     secondary= 28.8/44.8=64.3%    tertiary: 10/44.8=22.3%.       I have .5/114.23= 0.0043771 moles of dimethylhexane so I'm thinking I need to add that many moles of chlorine to the .5g of dimethylcyclohexane to get the total weight from which I will take my percentages.  With my percentages of that total weight I should be correct.....right?

[Dan]

       I have .5/114.23= 0.0043771 moles of dimethylhexane so I'm thinking I need to add that many moles of chlorine to the .5g of dimethylcyclohexane to get the total weight from which I will take my percentages.  With my percentages of that total weight I should be correct.....right?

If you have x mol of starting material you have x mol of products - if you calculate the molecular weight of the product you can calculate the mass of the product. Chlorine has replaced a hydrogen, it is not just a case of adding chlorine.

That gives you the masses of pri, sec and tert products, but the question asks for the mass of each unique chlorinated product - there several unique secondary chloride products.

[ish]

Thanks Dan- I thought about the different secondary products as I woke up this morning, weird how the human brain works....

I'm seeing four different secondary products (since stereoisomers aren't counted), I think that in reality steric hindrance would favor some over others but without that info I think I should just divide the total percentage of secondary products by 4 to get the occurance of each unique secondary product.

I understand what I got wrong about just adding the weight of chlorine, what you're saying is that x moles reagent A (the dimtheylcyclohexane for me) + x moles reagent B (the chlorine) = has to equal x moles product, so once I have the number of moles of product A I am good to go with simply that info.  Maybe I should review some Gen Chem over Christmas break

Thanks a ton for your help, I feel like I am usually 90% of the way there with these problems but with the way they grade us that doesn't come out to a 90% in grading