7
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I have almost the whole night trying to identify this structure with no avail as there is always one part that does not fit. The determined formula for this structure was $\ce{C13H17BrO}$ from the $m/z=268$ (M-100%), $m/z=269$ (M+1-14.7%), and $m/z=270$ (M+2-98.6%).

The $\ce{^1H}$-NMR data is as follows with integration in parentheses:

a. $\pu{7.30-7.27 ppm}$: multiplet (5) - arene with 5 hydrogens

b. $\pu{3.20 ppm}$: singlet (2) - R-CH2-Br attached to tetra-substituted carbon?

c. $\pu{2.45 ppm}$: triplet (2) - R-CH2-CH2-CO-CH3

d. $\pu{2.17 ppm}$: singlet (3) - R-CH2-CO-CH3

e. $\pu{1.68 ppm}$: sextet (2) - R-CH2-CH2-CH3

f. $\pu{0.90 ppm}$: triplet (3) - R-CH2-CH3

And this is the structure I come up with:

![enter image description here

which is the only structure that fits all the hydrogen integrations, but does not support the chemical shift at all.

I believe this is part of the molecule

enter image description here

because it takes care of shifts d,c,e,f. However, it is impossible to attach that structure to the remaining Arene, CH2-Br, and tetra substituted carbon. Actually spent over 6 hours on this problem and I'm losing my mind please help me.

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    $\begingroup$ You are just concerned with the shift of 2.45 right? I think your proposed structure does take care of that shift. The inductive effect of the carbonyl and the bromine atom may just be sufficient to cause such a deshielding effect. $\endgroup$ – Tan Yong Boon Oct 3 '19 at 11:31
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    $\begingroup$ c. 2.45 ppm triplet (2)- R-CH2-CH2-CO-CH3? $$$$ Did you mean R-CH2-CH2-CH3? $\endgroup$ – Karsten Theis Oct 3 '19 at 14:22
  • $\begingroup$ Did you deduce molecular formula by MS data or it is given? If so, I believe you may need additional decimal point on parent peak and others to do so. For example, ChemDraw is given M+1 peak as 14.1% instead of 14.7% on your data for $\ce{^{79}Br}$ containing peak. $\endgroup$ – Mathew Mahindaratne Oct 3 '19 at 16:39
  • $\begingroup$ Also, the part of molecule you are suggesting is a complete molecule. So, it can't be a part. $\endgroup$ – Mathew Mahindaratne Oct 3 '19 at 16:52
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    $\begingroup$ TanYongBoon Yeah, the shift at 2.45 doesn't really make sense according to this chart that I was given since a shift a 2.40 correlates to the CH2 attached to a carbonyl, but I too think its somewhat plausible that the 2.45 shift could be cause by deshielding thanks!. Karsten According to my proposed structure it is Ch2-ch2-ch3, but the ppm shift and splitting is more in line with the ch2 attached to a carbonyl, sorry I might have worded it strangely. Mathew I determined the formula from (M+1)/13 and 1:1 ratio of M to M+2 for 79 Bromine, but it didn't match up to the exact values! $\endgroup$ – Jonathan Joestar Oct 3 '19 at 22:25