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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: newbie! on May 30, 2011, 11:50:44 AM

Title: NMR help (13C and 1H)
Post by: newbie! on May 30, 2011, 11:50:44 AM

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added the stuff in red, but i cant get much further.
there are 7 shifts i need to assign, 2 on the aromatic (coz the other 2 are equivaelnt) but then there are 2 CH3's on plus another 1 on each side of the double bond? thats way more than 7.
help appreciated

Title: Re: NMR help (13C and 1H)
Post by: Dan on May 30, 2011, 03:17:03 PM

Quote from: newbie! on May 30, 2011, 11:50:44 AM

there are 2 CH3's on plus another 1 on each side of the double bond? thats way more than 7.

Remember, the three H atoms on a methyl group are almost always equivalent.

Title: Re: NMR help (13C and 1H)
Post by: newbie! on May 30, 2011, 04:17:54 PM

thx :)

so count them as 1 then?

oh and coupling confuses the s#*$ out of me  :s

help with this pls.
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a pic would be great.
i think across the double bond is 7, like trans across it. but they are all 7 i could be drawing 7's everywhere!?

Title: Re: NMR help (13C and 1H)
Post by: rucik5 on May 30, 2011, 07:15:08 PM

Hi. These are carboxylic acids, not aldehydes (but it doesn't matter). You're asked to provide the splitting pattern and integration (coupling pattern), draw the peaks. (The easy way do get there is to use any software [or webpage], draw the structure and 'predict' the NMR!) Four coupling - at this stage, only worry about the n+1 rule. What pattern would a single, isolated proton have? What about two protons next to three protons? And vice versa: three protons next to two protons? Then, consider chemical shifts; which protons would be most deshielded?