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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: Dolphinsiu on March 30, 2007, 08:23:38 AM

Title: Prediction for unknown cpd
Post by: Dolphinsiu on March 30, 2007, 08:23:38 AM
Deduce a structure consistant with the following data

C = 58.38%, H = 9.80% (C:H = 1:2)

(EI) m/z (abundance %): 207 (10), 205 (30), 204 (12), 192 (15), 190 (45), 170 (10), 164 (11), 162 (33), 157 (11), 156 (100)

(207:205 = 1:3, Cl is existed, 205 imply at least one N, 205 - 156 = 49 imply -CH2Cl fragmentation. The overall formula is C10H20NOCl)

IR (cm-1) : 2900, 1650

1H NMR (CDCl3):
1. 0.9 (6H,d)
2. 1.0 (6H,d)
3. 1.1 (3H,d)
4. 2.3 (1H,m)
5. 2.5 (2H,m)
6. 3.5 (2H, bd)

What I predict is:
                             
                                 (3)
       
                          CH3  CH3  O   
                           l       l      ll
(H3C)2 - N - CH2 - C  -   C  -   C - CH2Cl
                           l       l
                          CH3   H
 
   (2)           (5)    (1)    (4)         (6)

Does my prediction have problems?
Title: Re: Prediction for unknown cpd
Post by: Dan on March 30, 2007, 08:57:49 AM
Does my prediction have problems?

I'm afraid so. I don't have time to check this in detail right now, but...

Your structure is not consistant with your formula (no N in the structure).
You have a C with a valency of 5.

                     CH3  CH3  O   
                      l       l      ll
(H3C)2 - CH2 - C  -   C  -   C - CH2Cl
                      l       l
                     CH3   H

IR does not support the presence of a ketone. Looks like an amide.
Title: Re: Prediction for unknown cpd
Post by: Dolphinsiu on March 31, 2007, 03:54:06 AM
Sorry! I have not typed N (typing mistakes)

Title: Re: Prediction for unknown cpd
Post by: Dolphinsiu on March 31, 2007, 04:20:14 AM
                              O
                              ll
If 1650 really imply  - C - N (CH3)2


Fragmentation of -CH2Cl is still correct!

Then

I will predict
                       (4)
              CH3   H               O
              l         l                ll
Cl - CH2 - C  -    C -    CH2 -  C  - N - (CH3)2
              l         l
              CH3    CH3
      (6)    (1)      (3)     (5)                   (2)

Is my second prediction close to yours?

But from Mass spectrum

190 and 162 imply the loss of 15(CH3) and 43(COCH3) respectively!

So I still don't know the actual structure!
Title: Re: Prediction for unknown cpd
Post by: Dan on March 31, 2007, 06:33:58 AM
I don't think that structure accounts very well for the nmr data. The methyl groups on N would peak at higher ppm, and the splitting patterns are not consistent with that structure.

I haven't come up with anything that gives a good correspondance to the nmr data either. Are you sure that both 6H, d are in fact doublets and not two singlets?

ie. is it possible that 6H, d is actually 2 x 3H, s?
Can you get any more info on the structure of the multiplets?

Also, 43 in the MS could be an isopropyl group, Me2CH. An isopropyl group may also be responsible for a 6H, d in the nmr.
Title: Re: Prediction for unknown cpd
Post by: Dolphinsiu on March 31, 2007, 06:43:32 AM
I just copy from my past paper. I also don't have any idea in this question! Actually I am weak in predicting the unknown cpds!