A2 |Chemistry Mass Spectrometry Doubt(9701/42/O/N/12)

[mb1995]

I have a doubt in how to solve a question where they ask you to suggest a structure for an organic molecule through a Mass Spectrum of an NMR spectrum.
The following uploaded paper has a similiar question where my doubt initially originated.
(Question number 7C ,Section B, page 15 )
Please explain through reference to the question.
Thankyou~

P.S.
i have my exams this coming monday,i.e., 20/05/2013,so please help if you can before that date,
thankyou once again.

 

[iKhaled]

I have a doubt in how to solve a question where they ask you to suggest a structure for an organic molecule through a Mass Spectrum of an NMR spectrum.
The following uploaded paper has a similiar question where my doubt initially originated.
(Question number 7C ,Section B, page 15 )
Please explain through reference to the question.
Thankyou~

P.S.
i have my exams this coming monday,i.e., 20/05/2013,so please help if you can before that date,
thankyou once again.

alright bro..it is said that the m/e of M is 88 this means its molecular formula (Mr) of the organic compound.

lets calculate the carbon atoms present in the organic compound (1/1.1 x 0.22/5.1)x100 .. this is a formula which u need to learn and the answer will be 4 so we have 4 carbons present in the compound. now lets look at the amount of hydrogen atoms present..see the no on the top of the peak on each group in the NMR represent the amount of hydrogen present in that group so we have a group which has 3 and a group which has 2 and another group which has 3 so this makes a total of 8 hydrogen atoms present..

now we can predict the molecular formula of the compound 88-12(4)-8 = 32 so this 32 can represent the oxygen present for example we can have 32/16 = 2 so 2 oxygen atoms

so our molecular formula may be C4H8O2

lets do some identification using the NMR ... u can see the first peak which is a triplet has 3 hydrogen atoms present in it and it is a triplet so obviously the adjacent group attached to it must have 2 hydrogen atoms in it (applying the n+1 rule) which u need to learn too. now the second peak is a singlet peak with 3 hydrogen atoms present in it..this must be C=O group because any carbon bonded to an O doesnt give a division of peaks and it shows as singlet..the final peak is a quartet which means the adjacent group attached to it has 3 hydrogen atomatoms on it and u can see it also has 2 hydrogen atoms present in that group from here u can make up ur conclusion of this puzzle...

triplet peak is CH3 bonded to CH2
singlet peak is CH3COOR (use the data booklet)
quartet peak is CH2 bonded to CH3 so from here our organic compound will be CH3COOCH2CH3 which is ethyl ethanoate

got it ?

 

[mb1995]

Thanks, got it cleared, really appreciate your effort.