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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: Apple1977 on April 29, 2021, 12:21:02 PM

Title: IR Peaks
Post by: Apple1977 on April 29, 2021, 12:21:02 PM

Can somebody identify the following peaks please in the IR Spectrum .. can you give a full explanation  for each peak please ie C-H bend, Alkene etc …thank you

1068.2
1231.2
1367.1
1452
1733
2241.84
2921.11

Title: Re: IR Peaks
Post by: Apple1977 on April 29, 2021, 12:25:23 PM

I have them down as

OH Group
C-O stretch  ether
S=O stretch sulfonamide
C-H. Bend  Alkene methyl group
S=O. Stretch aldehyde
C (triple bond) N.  Stretch nitrile
C-H stretch Alkene

Can anyone put me right please

Title: Re: IR Peaks
Post by: Babcock_Hall on April 29, 2021, 02:14:54 PM

Not just the frequency but the depth (and occasionally the width) of the signal is extremely helpful in making assignments.  If an -OH group is present, what other signals would you see?

Title: Re: IR Peaks
Post by: Apple1977 on April 30, 2021, 10:49:00 AM

thanks for the info I already know ..lol.  the question was can anyone identify the correct assignments ?

I know about stretches and a-symmetric stretches etc etc ...dipole to dipole moment's strong weak and medium peaks .  all I would like is a professional second eye to look  on the peak assignments and report back . thank you  :D

dare I ask can anyone calculate this ???   I don't know where to start which is why there's no attempt

Water pH Titration Results

Exact concentration of NaOH solution: 0.100136 M

Volume of NaOH solution used in 1st titration: 22.4 mL

Volume of NaOH solution used in 2nd titration: 24.4 mL

Title: Re: IR Peaks
Post by: Babcock_Hall on April 30, 2021, 11:02:21 AM

If I were to assign a signal as C-O, what should I look for next?

I don't know what you mean by S=O aldehyde.  Is that a typo?

More generally, I would say that any one stretch frequency might be associated with one or possibly more than one functional group, depending on the particulars. 

Title: Re: IR Peaks
Post by: Borek on April 30, 2021, 12:56:02 PM

Quote from: Apple1977 on April 30, 2021, 10:49:00 AM

Water pH Titration Results

Exact concentration of NaOH solution: 0.100136 M

Volume of NaOH solution used in 1st titration: 22.4 mL

Volume of NaOH solution used in 2nd titration: 24.4 mL

Huh?

Title: Re: IR Peaks
Post by: Apple1977 on May 01, 2021, 05:12:34 PM

Sorry guys I’m Forensic’s so maybe these are not familiar areas of expertise for you

Title: Re: IR Peaks
Post by: Borek on May 01, 2021, 05:59:02 PM

IR spectra of a compound doesn't depend on the application. There is often no easy and unique peak assignment, IR can be quite messy.

Title: Re: IR Peaks
Post by: Babcock_Hall on May 02, 2021, 09:00:52 AM

I recently started teaching forensic chemistry, and IR is one of the topics, as well as being part of the organic chemistry curriculum that I have taught for some time.  It seems to me that you approaching this problem with the wrong tactic.  You should be working toward finding a single structure that is compatible with all of the available evidence.  That is why I was prodding you about C-O and O-H groups.

With respect to your titration results, I don't understand the context of the question.  Once you fill that in, Borek should be able to guide you.