Nmr =/

[Tina324]

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CH3-CO-CH2-O-CH3
I don't understand how this has 3 triplets

CH3-CH2-O-CH2-CH3
i don't understand how this has 2 singlets

How the heck do you determine if something is s singlet, doublet, triplet..etc. I don't get them right every time, so i guess i am off with my method.

hellllp!!!..please

 

[anesthesia_209]

CH3-CO-CH2-O-CH3
I don't understand how this has 3 triplets

CH3-CH2-O-CH2-CH3
i don't understand how this has 2 singlets

How the heck do you determine if something is s singlet, doublet, triplet..etc. I don't get them right every time, so i guess i am off with my method.

hellllp!!!..please

I think the first one should have 3 singlets and the second should be a triplet and a quartet.

Just look for hydrogens. If they are chemically similar (i.e. bonded to the same atom or the molecule is symmetrical) then they will show up in the same peak but will have different magnitude (peak will be higher). This will tell you how many peaks you have.

To determine multiplicity (triplet, quartet, doublet, etc.) you start from the atom that is bonded to the hydrogen and look at the nearby atoms and determine how many hydrogens there are. This will tell you the multiplicity (the number of nearby hydrogens +1 will tell you the multiplicity of the peak - this is related to the different number of ways the nearby hydrogens can affect the hydrogen you are primarily looking at (spin coupling). This is related to the pascal triangle but I don't think you need to go that indepth, just remember the +1 rule.

 

[Mamona]

Can the first one have 2 singlets and 1 triplet?
The second one I agree it has 1 triplet and one quartet

 

[Tina324]

I think the first one should have 3 singlets and the second should be a triplet and a quartet.

Just look for hydrogens. If they are chemically similar (i.e. bonded to the same atom or the molecule is symmetrical) then they will show up in the same peak but will have different magnitude (peak will be higher). This will tell you how many peaks you have.

To determine multiplicity (triplet, quartet, doublet, etc.) you start from the atom that is bonded to the hydrogen and look at the nearby atoms and determine how many hydrogens there are. This will tell you the multiplicity (the number of nearby hydrogens +1 will tell you the multiplicity of the peak - this is related to the different number of ways the nearby hydrogens can affect the hydrogen you are primarily looking at (spin coupling). This is related to the pascal triangle but I don't think you need to go that indepth, just remember the +1 rule.

oops sorry you are right. the first one is 3 singlets, but i don't understand why? wouldn't the methyon the left of the carbonyl exhibit a triplet b./c the CH2 is 2 bonds away? shoulnd't the CH2 exhibit a quartet because the CH3 is 2 bonds away? and shouldn't the methy attached to the O exhibit a triplet?

also, the second one...destroyer says it yields 2 singlets which makes noooo sense.

thank youuuu soo much for answering my questions. I have yet another:

Ph-O-CH2-CH2-CH3
when im tyring to figure out the multiplicity of the CH2 attached to the O, do I look at the H's attached to the Ph group, or the H's attached to the other CH2?

 

[tranv117]

the trick to H coupling is that the Hs can only be separated by THREE BONDS, well this is what I learned through Kaplan and is hasnt failed me yet.

 

[anesthesia_209]

oops sorry you are right. the first one is 3 singlets, but i don't understand why? wouldn't the methyon the left of the carbonyl exhibit a triplet b./c the CH2 is 2 bonds away? shoulnd't the CH2 exhibit a quartet because the CH3 is 2 bonds away? and shouldn't the methy attached to the O exhibit a triplet?

also, the second one...destroyer says it yields 2 singlets which makes noooo sense.

thank youuuu soo much for answering my questions. I have yet another:

Ph-O-CH2-CH2-CH3
when im tyring to figure out the multiplicity of the CH2 attached to the O, do I look at the H's attached to the Ph group, or the H's attached to the other CH2?

Must be a mistake on the second one.

What I meant by 2 bonds away is that you start from the hydrogen atom and you stop at the atom that is two bonds away and count how many hydrogens are attached to it (some use a 3 bonds away method that goes directly to each hydrogen).

The easiest way to do it is-for example look at the CH3. To determine the multiplicity of these 3 hydrogens on this carbon, you look at the closes atoms bonded to the carbon. There's only a CH2. Since this has two hydrogens, you will have a multiplicity of 3 (n+1) for the CH3. That means that the peak corresponding to the CH3 hydrogens will have an integration (magnitude) of 3 and a multiplicity of 3 (a triplet). Not sure if you have to worry about integration on the DAT though...

For the CH2 attached to the O, atoms nearby are an O and a CH2, total of 2 hydrogens, so it will also have a multiplicity of 3 but it will have an integration of 2.

 

[Mamona]

the trick to H coupling is that the Hs can only be separated by THREE BONDS, well this is what I learned through Kaplan and is hasnt failed me yet.

What do you mean separated by 3 bonds

 

[Dencology]

yes. you are right.

Can the first one have 2 singlets and 1 triplet?
The second one I agree it has 1 triplet and one quartet

 

[Tina324]

ughh ok my head is spinning...bear with me please lol

CH3-CO-CH2-O-CH3

red CH3=triplet because 2 bonds to the right is a carbon with 2 H's?
green CH3=?? do i look left on right for this one?
purple CH3=triplet because 2 bonds to the left is a carbon with 2 H's?

thanks

 

[tranv117]

just think how many bonds separate two Hs for coupling.

Like for this example,
CH3-CO-CH2 ==> between the H of CH3 and H of CH2, there are 4 bonds separating the two Hs...draw it out and you'll see what Im talking about. Since more than 3 bonds, the two Hs will not couple. I believe it has to do with electron density. The further the Hs are away from each other, the less each H has an effect on one another so therefore they won't couple.

I think the easiest and best way to understand HNMR is Kaplan Online if you have it.

 

[Mamona]

just think how many bonds separate two Hs for coupling.

Like for this example,
CH3-CO-CH2 ==> between the H of CH3 and H of CH2, there are 4 bonds separating the two Hs...draw it out and you'll see what Im talking about. Since more than 3 bonds, the two Hs will not couple. I believe it has to do with electron density. The further the Hs are away from each other, the less each H has an effect on one another so therefore they won't couple.

I think the easiest and best way to understand HNMR is Kaplan Online if you have it.

I think I understand what you're saying, but going back to the OP example what is the answer 2 singlets and one triplet???

 

[Mamona]

ughh ok my head is spinning...bear with me please lol

CH3-CO-CH2-O-CH3

red CH3=triplet because 2 bonds to the right is a carbon with 2 H's?
green CH3=?? do i look left on right for this one?
purple CH3=triplet because 2 bonds to the left is a carbon with 2 H's?

thanks

If I am understanding right
red CH3 = singlet because doesn't couple due to the 4 bonding separation
green CH2 = singlet, but I don't know the reason why you look to the left?
purple CH3 = triplet due to the green CH2

 

[Tina324]

ohhhh ok i think im starting to get it...dude u are helping me SOOO much, i can't thank you enough.

What i don't get though is whether i should look at the hydrgens at the left or the right to determine multiplicty. for example:

Ph-O-CH2-CH2-CH3
is the COLOR="Red"]CH2[/COLOR] a triplet or quartet (and why?)
also are the H's on the phenyl..singlets?

one more q (relates to the q above)
CH3-CH2-O-CH2-CH3
is the CH2 a triplet or quartet? can't it be either?

thanks again!

 

[anesthesia_209]

ughh ok my head is spinning...bear with me please lol

CH3-CO-CH2-O-CH3

red CH3=triplet because 2 bonds to the right is a carbon with 2 H's?
green CH3=?? do i look left on right for this one?
purple CH3=triplet because 2 bonds to the left is a carbon with 2 H's?

thanks

Scratch the whole two bonds thing. Do it the easy way. Just look at the atoms to the immediate left and to the right of it.

Say you want to figure out the multiplicity of the Red CH3, look to the left and right of the carbon. All you have is CO, which isn't attached to any hydrogens, so you will have a singlet (n+1).

With the Green CH2, look to the immediate left and right. To the left, you have CO and to the right you have an O. Neither of which is attached to a hydrogen. This will also be a singlet.

Now for the Purple CH3, you also get a singlet because none of the nearby atoms are attached to a hydrogen.

That results in 3 singlets.

 

[Tina324]

Ohh ok so the CH2 in CH3-CH2-O-CH2-CH3 will be a quartet because the closest atom with H's is CH3 and has 3 of them ..therefore quartet.

what about this one....
Ph-O-CH2-CH2-CH3
are the H's on the phenyl..singlets?
the 1st CH2 is a triplet?
the 2nd CH2 is a quartet? (can't it be a triplet too?)
the CH3 is a triplet?

thank uuuuuu

 

[anesthesia_209]

ohhhh ok i think im starting to get it...dude u are helping me SOOO much, i can't thank you enough.

What i don't get though is whether i should look at the hydrgens at the left or the right to determine multiplicty. for example:

Ph-O-CH2-CH2-CH3
is the COLOR="Red"]CH2[/COLOR] a triplet or quartet (and why?)
also are the H's on the phenyl..singlets?

one more q (relates to the q above)
CH3-CH2-O-CH2-CH3
is the CH2 a triplet or quartet? can't it be either?

thanks again!

You have to consider both sides. The red CH2 will be a sextet because it is nearby 5 hydrogens (5+1 = sextet).

For the phenyl group, you will have doublets and triplets. Two of the hydrogens have only 1 total hydrogen attached to the nearby carbons where as 3 have 2 hydrogens on the nearby carbons. They'll make roughly 3 peaks (2 of which will probably partly overlap) due to shielding/deshielding effects but you don't need to go that deep into it.

For the last question, the CH2 is a quartet because it has 3 total hydrogens on nearby atoms (3 from CH3 and 0 from O). Remember that both CH2's will only represent one quartet in the NMR though because the molecule is symmetrical.

 

[AndyK]

Scratch the whole two bonds thing. Do it the easy way. Just look at the atoms to the immediate left and to the right of it.

Say you want to figure out the multiplicity of the Red CH3, look to the left and right of the carbon. All you have is CO, which isn't attached to any hydrogens, so you will have a singlet (n+1).

With the Green CH2, look to the immediate left and right. To the left, you have CO and to the right you have an O. Neither of which is attached to a hydrogen. This will also be a singlet.

Now for the Purple CH3, you also get a singlet because none of the nearby atoms are attached to a hydrogen.

That results in 3 singlets.

I second this motion

 

[anesthesia_209]

Ohh ok so the CH2 in CH3-CH2-O-CH2-CH3 will be a quartet because the closest atom with H's is CH3 and has 3 of them ..therefore quartet.

what about this one....
Ph-O-CH2-CH2-CH3
are the H's on the phenyl..singlets?
the 1st CH2 is a triplet?
the 2nd CH2 is a quartet? (can't it be a triplet too?)
the CH3 is a triplet?

thank uuuuuu

The second CH2 will be a sextet because of the CH2 and CH3 (total of 5 hydrogens). Apart from that the rest are right.

 

[AndyK]

Also, you have to remember the hydrogens on the phenyl. The ortho hydrogens will produce a doublet; the meta hydrogens a triplet; the para hydrogen will make a doublet even though there are two adjacent hydrogens because those hydrogens are equivalent.

 

[Tina324]

you guys are amazing. you have cleared up so much for me.

there seems to be a discrepancy between you guys tho....does the phenyl have 3 triplets a 2 doublets OR 3 doublets and 2 triplets?

 

[anesthesia_209]

you guys are amazing. you have cleared up so much for me.

there seems to be a discrepancy between you guys tho....does the phenyl have 3 triplets a 2 doublets OR 3 doublets and 2 triplets?

3 triplets and 2 doublets but since it's symmetrical, it will be 2 triplets and a doublet.

The para hydrogen will be a triplet. Only take symmetry into consideration when you want to know the number and integration of peaks.

 

[Tina324]

oOo kk.

hmm what else do you think is important to know for NMR? i think i can read the graphs (deshielding, the higher the peak the more of that type of H). is that it?

 

[utdent20]

I have a tough time with the those peaks in Cnmr and Hnmr.. any one got any examples we could discuss?

 

[utdent20]

hey Tina,, it seems you've got it.. can you help me out with this post.. i was following along until i lost it with the new sets of problems you posted on this tthread..

 

[Tina324]

haha i will try my best. I hope I have it! test in 3 days!! ahh
kk repost the ones you don't understand and please please post others if you have, so that we can practice.

=)