H NMR question regarding signals

[inquiry101]

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so if i have 1-chloropropane and 2-chloroproprane, how many NMR signals would each of these compounds display?


this question was taken from the TPR science workbook, orgo passage 6, question 5. The answer is 3,2

however, i am getting 4 signals for 1-chloropropane and 3 signals for 2-chloroproprane by using the n+1 rule for neighboring hydrogens.


Please help!

 

[vayntraubinator]

so if i have 1-chloropropane and 2-chloroproprane, how many NMR signals would each of these compounds display?


this question was taken from the TPR science workbook, orgo passage 6, question 5. The answer is 3,2

however, i am getting 4 signals for 1-chloropropane and 3 signals for 2-chloroproprane by using the n+1 rule for neighboring hydrogens.


Please help!

propane implies 3 carbons, so there should be 3 equivalent sets of hydrogens.

Cl-CH2-CH2-CH3

For 2-chloropropane we have:

CH3-CH(Cl)-CH3

The two CH3's on each side of propane are symmetrical with respect to the chlorine so they compose of 1 chemically equivalent group. The hydrogen attached to the carbon attached to the chlorine counts as one group. Thus there are 2.

Dont use N+1 rule for finding number of signals. That rule is used just to find the splitting of a particular signal

 

[MShopes]

so if i have 1-chloropropane and 2-chloroproprane, how many NMR signals would each of these compounds display?


this question was taken from the TPR science workbook, orgo passage 6, question 5. The answer is 3,2

however, i am getting 4 signals for 1-chloropropane and 3 signals for 2-chloroproprane by using the n+1 rule for neighboring hydrogens.


Please help!

1-chloropropane is 3 signals...3 different types of H's...Two H's are connected to the Cl, thats the first type of H, then two H's in the second carbon which is the second type of H's and then the third carbon contain three H's which are different than the second carbon H's because the second carbon H's are closer to Cl.

2-chloropropane is 2 signals....2 different types of H's-watch the symmetry on both sides and how the 3 H's on both side are the same. On each side, the two carbons contain 3 H's that are the same because they are both connected to two carbons that are connected from right and left to a middle carbon atom containing one H and one Cl. And the second type of H is the H on the carbon directly containing the Cl.

Hope this helps!

Don't use any rules for this as vayntraubinator just said....instead use common sense and concept combined.

 

[salim271]

I agree with the above posts. I find it best to just remember the way NMR works, it only looks at protons, so just figure out which protons are giving different signals.

 

[inquiry101]

thanks a lot guys, i appreciate it

 

[BilalL]

Looking for symmetry is key in these problems. First notice that the H's on the C with Cl must have a unique signal. So the task is just identifying if the other protons are symmetrical or not.