Chemical Forums

Please login or register.

Login with username, password and session length

Sponsored links

Pages: [1]   Go Down

Author Topic: NMR spectrum of aldehyde!  (Read 5558 times)

0 Members and 1 Guest are viewing this topic.

Winga

  • Chemist
  • Full Member
  • *
  • Mole Snacks: +39/-10
  • Offline Offline
  • Posts: 510
NMR spectrum of aldehyde!
« on: July 26, 2004, 06:28:15 PM »

In a class test. I need to find out the structural formula of a compound with providing the empirical formula (C5 H10 O), IR spect, NMR spect and mass spect.

The answer is 3-methylbutanal.

(CH3)2-CH-CH2-CHO

In NMR sepct, there should be 4 signals. The aldehydic proton has a chemical shift around 9. However, there is no spin-spin coupling between aldehydic proton and methylene protons (nearby protons).

Theorectically, the signal of aldehydic proton should be present as triplet and the methylene protons is also triplet (another methine proton just next to them).

In this spect, the signal of aldehydic proton is singlet while the methylene protons is doublet. An explanation from someone is that, there is oxygen affect that proton. But I don't think this case is as same as the high concentrated / pure alcohol which gives no coupling and the effect of magnetic anistropy by C=O double bond only reinforce the applied magnetic field that the proton feels.

The answer 3-methylbutanal is correct and the NMR spect is made by real experiment. So, how to explain it?
« Last Edit: July 26, 2004, 06:44:49 PM by Winga »
Logged

Organic_lover*

  • Regular Member
  • ***
  • Mole Snacks: +1/-2
  • Offline Offline
  • Gender: Female
  • Posts: 14
Re: NMR spectrum of aldehyde!
« Reply #1 on: January 21, 2012, 01:57:36 PM »

You can find the aswer to your question in this book:

Introduction of Spectroscopy
Donald Pavia and Gary Lampman
Logged
"Nothing in life is to be feared, only understood. Now is the time to understand more to fear less." {Marie Curie}

dipesh747

  • Regular Member
  • ***
  • Mole Snacks: +7/-5
  • Offline Offline
  • Posts: 89
Re: NMR spectrum of aldehyde!
« Reply #2 on: January 23, 2012, 03:37:26 AM »

Look up the Karplus relation
Logged

AWK

  • Global Moderator
  • Sr. Member
  • ***
  • Mole Snacks: +357/-108
  • Offline Offline
  • Gender: Male
  • Posts: 4858
Re: NMR spectrum of aldehyde!
« Reply #3 on: January 23, 2012, 04:01:26 AM »

It depends on quality of spectrometer
http://www.ymdb.ca/spectras/2496
Logged
AWK

orgopete

  • Chemist
  • Sr. Member
  • *
  • Mole Snacks: +177/-64
  • Offline Offline
  • Posts: 2133
    • Curved Arrow Press
Re: NMR spectrum of aldehyde!
« Reply #4 on: January 23, 2012, 09:07:33 AM »

It depends on quality of spectrometer
http://www.ymdb.ca/spectras/2496

Isn't the J-value of the aldehyde 3Hz? Shouldn't you be able to see that with almost any spectrometer of the last 50 years?
Logged
Author of a multi-tiered example based workbook for learning organic chemistry mechanisms.

AWK

  • Global Moderator
  • Sr. Member
  • ***
  • Mole Snacks: +357/-108
  • Offline Offline
  • Gender: Male
  • Posts: 4858
Re: NMR spectrum of aldehyde!
« Reply #5 on: January 24, 2012, 09:24:26 PM »

It depends on quality of spectrometer
http://www.ymdb.ca/spectras/2496

Isn't the J-value of the aldehyde 3Hz? Shouldn't you be able to see that with almost any spectrometer of the last 50 years?
but Winga wrote:
Quote
The aldehydic proton has a chemical shift around 9. However, there is no spin-spin coupling between aldehydic proton and methylene protons (nearby protons).
Logged
AWK

discodermolide

  • Chemist
  • Sr. Member
  • *
  • Mole Snacks: +369/-67
  • Offline Offline
  • Gender: Male
  • Posts: 4565
    • My research history
Re: NMR spectrum of aldehyde!
« Reply #6 on: January 25, 2012, 08:03:01 AM »

Is the aldehyde signal not an ABq where the J value is very small and you only observe the middle two lines?
I have spectra of aldehydes on this computer where the aldehyde signal appears to be a doublet. (Sorry I forgot to include the scale but the signal is at 9.5 around)
Logged
Development Chemists do it on Scale, Research Chemists just do it!
My Research History
Pages: [1]   Go Up
 

Mitch Andre Garcia's Chemical Forums 2003-Present.

Page created in 0.114 seconds with 24 queries.