[help22]

Hey,

I am having a bit of trouble identifying to unknown compounds. From the tests I have done I am still unsure of what they could be.

Unknown A: is a clear liquid that is souable in NaOH, NaHCO3, and has a boiling point above 100. I have come to the conclusion that it is a carboxcylic acid. Also the IR is 3420 and the PRM is as follows- 1.0 t 3H
                                                        1.5 d 3H
                                                        2.0 m 2H
                                                        3.6 m 1H
                                                        4.4 s, 1H

Unknown B: this one is a bit easier for me to deal with. It is a yellow powder that is insouable in NaOH, NaHCO3, but not in H2SO4. I have concluded that it is a ketone. Also the melting point is around 90 but I believe this was an error cause the machine was turned on and off a few times in a row. The IR is 1715 and the PMR is as follows- 2.1 s 3H
                         6.9-7.4 m, 4H.
I think that unknown B may be biphenyl but I am not sure. Can anyone help me figure out what these unknowns are?

Thanks

[Nick]

For A, please post your PRM solvent.

For B, I am confused.  You conclude that it is a ketone and then propose biphenyl.  Biphenyl has no carbonyl, but you corrected concluded that the IR indicates a ketone.  It looks to me like methyl phenyl ketone, CH3(CO)(C6H5).  This would give a singlet for the methyl group.  However, you would expect 5 aromatic protons and you report only four.  Double check your results and see if you integrated correctly.  If you are sure there are only four aromatic protons, you might have a halogen on the benzene ring meta to the acetyl group.

[kiwi]

for unknown A, what are the other significant peaks in the IR?

[macman104]

This is a great site.  Helped me out many a time.

For A, the triplet/doublet group at 1 and 1.5, are probably an ethyl group.  Also, if you are assuming it is a carboxylic acid, do you by chance have a peak far downfield, in the 10-11 region?  Also, there needs to be a peak in the 1700-1720ish peak for the C=O bond in the acid.

[help22]

Well for unknown B I did certian tests to figure out if it was an alcohol, alkene, aldehyde, or ketone. The TA confirmed it was a ketone when I asked her. With the IR and PMR data the information that I posted was all that I was given. I assumed its biphenyl because in the procedure it says that if the substance is negative it is biphenyl. And I also looked up the physcial chracteristics of it and it says that it is a yellow powder. So I have no idea if i am right. I did the melting point but again I feel like it was inacurate it ranged from 75 to 90.


the IR is 1715            PMR is                   2.1 s 3H
                                                          6.9-7.4 m, 4H       

For Unknown A, all I know is that it is a soulable in practaically everything and it is aclear liquid. It formed bubbles when I put NaOH in the soultion which indicated that it had a carboyxlic acid.

the IR is 3420            PMR is                 1.0 t 3H
                                                        1.5 d 3H
                                                        2.0 m 2H
                                                        3.6 m 1H
                                                        4.4 s, 1H


Basically I just have to figure out the names of these compounds and I am stuck.

[Custos]

You're stuck because you don't have enough information. For compound A the PMR is consistent(ish) with a secondary butyl group

CH₃-CH₂-CH(CH₃)-R

The first CH₃ would be a triplet, the CH₂ would be a multiplet as would the CH and the second CH₃ would be a doublet, all at around the right resonance, depending on what R is. The only inconsistent things are the one proton singlet at 4.4, and as macman104 said, the absence of your COOH resonance.

For compound B the PMR looks like a methyl and a disubstituted benzene ring. If the compound is indded a ketone then a substituted methyl phenyl ketone would fit. What the added substituent is however is hard to guess. It could be p-nitroacetophenone for example, which is a yellow solid melting around 80^o.

[macman104]

I hope you don't mind me copying the relevant parts of your PM to me, but some parts of your PM didn't make sense, and I thought some of the info in it may be helpful to others trying to assist you.  In your PM, you say:

unknown A- I think is 1-butanol.

All i know about the formula is that there are 10 H's and a O somewhere.

The Pmr is as follows and the IR is 3420.
1.0 t, 3H
1.5 d, 3H
2.0 m, 2H
3.6 m, 1H
4.4 s, 1H exch.
The compound is clear and forms bubbles which means it is carboxcylic acid.

Stop.  You say you think it is 1-butanol, but then say because it forms bubbles it is a carboxcylic acid.  1-butanol is not an carboxcylic acid.  Also, what do you mean by the abbreviation "exch."  If it is an alcohol, that may possibly be the OH group, and would also explain your IR peak.  Last part of your PM...

For compound B I am totally lost. I think the formula is either C8H7ClO or C8H7O.

the PMR is 2.1 s 3H
               6.9 - 7.4 4H
IR 1715.

You keep stating what your IR is.  I was wondering, do you have a printout from doing an IR scan, or do you just have a list given to you of what peaks are there?  If you have an actual scan, can you please list other peaks that are present, especially for compound A.  Take a look at hexanoic acid  If you look at the 1H NMR (Which, btw, I've never heard referred to as PMR, *shrug*), and the IR, you will see the result of a typical alkyl acid.  See the big peak in the IR at 1700?  Do you have one like that?

There should be more than just the one peaks in the IR, that are noteworthy, so if you have access to them, listing other peaks may be helpful.  Or, if you can do even better, and scan them, that works also.  More info would be very helpful.

[help22]

It is just a list not a chart so I am unable to see where any peaks are. And I am assuming the exch means it turns into an alcohol.

[sjb]

... If you look at the 1H NMR (Which, btw, I've never heard referred to as PMR, *shrug*)...

Just shorthand for Proton Magnetic Resonance, nothing fancy

S

[Custos]

It is just a list not a chart so I am unable to see where any peaks are. And I am assuming the exch means it turns into an alcohol.

"exch" means the proton resonance will disappear if you add D₂O. i.e the proton is "exchangeable" in water. Protons that are exchangeable are generally those attached to heteroatoms (N, O, S)... so groups such as -OH, COOH, NH₂ and so on. Usually protons attached to carbon atoms do not exchange, unless they are enolisable.