Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Organic Spectroscopy => Topic started by: xxdesigulxx on December 09, 2012, 11:11:20 PM
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Hi guys,
I need help identifying the product from the spectra. we did a lab on synthesis of benzyl alcohol(preparing benzyl alcohol from benzyl chloride),
Can some please help me identify the functional groups and the Product using the IR, NMR, and Mass spectrum.
Here are the links :
http://oi50.tinypic.com/5mzrpx.jpg (http://oi50.tinypic.com/5mzrpx.jpg) <-IR spectrum
http://tinypic.com/r/hvo4tj/6 (http://tinypic.com/r/hvo4tj/6) <- mass S
http://tinypic.com/r/2qcnq5x/6 (http://tinypic.com/r/2qcnq5x/6) <- HNMR
thanks. one more thing the boiling point obtained was 160c!. please help me!. Thank you!
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What groups have you identified up to now?
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You have to show your attempts at solving the question to receive help. This is a forum policy, described in the forum rules (http://www.chemicalforums.com/index.php?topic=33740.0).
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Hi.
i was able to identify o-h (between 3400-3500), c-h (2800-3000), c-o(1100-1300)I dont know if i am rightIn hnmr the gap describes that there is unknown element present. So how can i use the mass spectrum to finthat? In mass spec. The parent peak is 122.so like is that the molar mass. I dont get it.
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I do not see an OH stretch in the IR.
The peak at m/e = 91 tells you something. You have the MWt. 122, what fragment could be lost here?
What information can you get from the NMR?
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91 m/z is the base peak i think it tells you that there is benzyl unit present there. NMR there are 3 peaks so, 3 H present there, but i dont know how i can get the formula from there!:(
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That's right the m/e at 91 is a benzyl radical cation, this fits with the NMR showing 5 aromatic protons.
So you have C6H5-CH2-unknown-unknown.
So what could the unknowns be, does the loss of 31 in the mass. spec say anything? Along with 2H and 3H in the NMR.
Have a guess.
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is it due to ester?
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No it is not an ester.
What compounds do you know with a mass of 32?
In the NMR both peaks are singlets. That is no coupling between them. The position of the 2H signal at 4.4 should indicate something to you.
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oh its sulfur. and the the position of 2h at 4.4 tells us that there is formaldehyde, ch2o present. am i right?
Thank you for immediate response. you are a big help. thanks so much!:)
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No it is not sulphur, it is an organic fragment.
Formaldehyde is not present it is though CH2O.
So we have C6H5CH2O-unknown. The unknown part has 3 protons in it.
add up the mass of C6H5CH2O and see what is left.
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the mass of that comes up to 107. so 122-107=15.
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lithium is the one that has 3 protons
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Right, so which organic unit has a mass of 15, knowing that there are 3 protons in that fragment?
Look by protons I mean H atoms, you are looking at a proton NMR
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i dont get it!:(
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The fragment has a mass of 15 and contains 3 hydrogen atom, you know this from the hydrogen (proton) NMR.
so we have C6H5CH2O-Unknown fragment of mass 15 containing 3 hydrogen atoms.
what is this unknown fragment of mass 15 containing 3 hydrogen atoms?
Put it another way you have calculated 107 mass before, plus 3 gives 110, leaving 12!
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lithium?
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Which element has a mass of 12?
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please ignore the last comment i wrote. i wrote that earlies. Carbon has a mass of 12
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Right,
so we now have
C6H5CH2-O-CH3, (methoxymethyl)benzene is your unknown.
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omg thank you so much. It is same as methoxytoluene right? and am i missing something from the IR Spectrum? meaning did i name the functional groups right beside the alcohol?
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The IR does not really tell you much apart from the presence of an aromatic C=C. apart from the OH mistake it's ok.
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thank you so much for your help.
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My pleasure.
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The IR does not really tell you much apart from the presence of an aromatic C=C. apart from the OH mistake it's ok.
I do not conclude the IR shows an OH group is present. It is valuable to compare actual spectra with different functional groups to help estimate the magnitude of absorptions. The OH band is rather small compared to the relatively weak CH bands. Overtones and water can give weak absorptions. If an alcohol were present, you would find an OH band is much stronger than than even multiple CH absorptions.
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Orgopete, did you actually read the entire post? Replies 3 & 4 especially, number 3, from the OP said there was an OH present, number 4, I corrected him and said there was no OH.
So I don't really understand your comment.
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Orgopete, did you actually read the entire post? Replies 3 & 4 especially, number 3, from the OP said there was an OH present, number 4, I corrected him and said there was no OH.
So I don't really understand your comment.
Yes, and I looked at the spectrum. The poster also looked at the spectrum and had concluded the weak band around 3300 cm-1 Indicated an OH. Could both be correct? I presumed the poster was inexperienced and thought the weak peak could have been an OH. My comment was directed to that audience to help them distinguish between an alcohol and the instance in which the some environmental OH or even an overtone of a carbonyl compound could leave a small and weak peak in the OH region.
Please check the spectrum yourself and tell us if the poster mistakenly reported the wrong frequency.
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Thank you for the clarification, it was not clear to whom you were addressing the comment.
The very small peak in the IR which the poster recorded as being between 3400-3500 cm-1is very likely traces of water, certainly not an alcohol, which is much more intense. Certainly the OH stretch lies within this region.