Question

2. Answer the following questions for an unknown with molecular formula C HBrO2 given the spectral data below: (a) Calculate the molecular weight and the exact mass of the compound. (b) Deduce the structure. Relative Abundance percent) (166) Om 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 triplets

Answer 1

Hi Dear Friend, the unknown identified as methyl 3-bromopropionate

Н.С Br.

a)

Given molecular formula = C₄H₇BrO₂

molecular weight = [(4 x C) + (7 x H) + (1 x Br) + (2 X O)]

= [(4 x 12.0107 ) + ( (7 x 1.00794 ) + (1 x 79.904 ) + (2 x 15.9994 )] = 167.0012 g/mol

considering stable isotopes of C (12), H (1), Br (79), O (16), the exact mass of compounds is also 167.0012 g/mol

b)

m/z 166 - m/z 135 = 31 indicates loss of H₃CO⁺ fragment

m/z 166 - m/z 107 = 59 indicates loss of H₃C-O-CO⁺ fragment

m/z 87 is base peak which is result of a loss of Br from m/z 166 ( 166 - 79 = 87)

m/z 15 (CH3), m/z 29 (CH3-CH2-)

HNMR:

there are only 3 signals 3H, singlet; 2H, triplets - two suggesting a methyl ester

methyl 3-bromopropionate 0- HC- (A) 0-CH2-CH2-B1 (C) (B) Assign. Shift (ppm) 3.7 lo in 9 8 7 6 5 4 3 1/1 ppm

Hope this helped you!

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