# Identifying Structure based off 1H-NMR & Mass Spectroscopy Data [closed]

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:

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

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.

• 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. – Tan Yong Boon Oct 3 '19 at 11:31
• c. 2.45 ppm triplet (2)- R-CH2-CH2-CO-CH3?  Did you mean R-CH2-CH2-CH3? – Karsten Theis Oct 3 '19 at 14:22
• 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. – Mathew Mahindaratne Oct 3 '19 at 16:39
• Also, the part of molecule you are suggesting is a complete molecule. So, it can't be a part. – Mathew Mahindaratne Oct 3 '19 at 16:52
• 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! – Jonathan Joestar Oct 3 '19 at 22:25