Question

Using the provided MS and IR spectra, predict the structure and identity of the unknown. Show all workings and reasoning. Identify important peaks or fragments that led to your conclusion. You are free to use Rule 13 and/or index of hydrogen deficiency when necessary.

0 1 73 O + 65% CHM 341: Organic Chemistry I. MS-IR Homework. Using the provided MS and IR spectra, predict the structure and identity of the following unknowns. Show all workings and reasoning. Identify important peaks or fragments that led to your conclusion. You are free to use Rule 13 and/or index of hydrogen deficiency when necessary. Note that, in some cases, more than one structure may be correct 1. Unknown A 8 Relative Intensity $ 0- Hhhh 40 50 60 70 m/z TRANSHEIM

Answer 1

M+ = 98
Rule of 13: devide 98 by 13 we get: n=7 and remainder is r=7
Empirical formula is = CnHn+r = C7H14
IR shows peak 1720 means there is a carbonyl group present. Hence add one oxygen by replacing CH4: C6H10O
Degree of unsaturation = ((2C+2)+N-H-X)/2 = (14+0-10-0)/2 = 2
There are two sites of unsaturation.
IR shows carbonyl peak so one site is accounted there and hence remaining site may be for one ring.
IR: 2950 and 2850: sp3 C-H stretching
1720: C=O stretching
1450: CH2 scissoring
1350: C-H bending
a small peak at 3400 indicates the overtone of ketone C=O.

Mass analysis:

M (98) mz = 55 mz = 42 mz = 70 20 30 40 50 60 70 80 90 100

mz = 55 - 一一.一 一.. mz = 70 -CO m/z = 42

Thus the compound is cyclohexanone.