Question

8) Propose a structure for the compound with IR, NMR, and mass spectra shown below. The integration of the peaks is in arbitrary units above them. 18 marks (Hint: check for possible isotopes in MS) 2400 2100 1800 1500 1200 900 600 300 OHz 12007 19554 J = 6.6 Hz 6667 5768 J = 6.6 Hz LLLLLLLLLL LLLLLLLLLLLLLLLLLLL Oppm (8) wavelength, micrometers 5 5.5 6 7 8 2.6 2.8 3 3.5 4 4.5 9 10 11 12 13 14 1516 100 percent transmittance 800 600 3800 3400 3000 2600 2200 2000 1800 1600 1400 1200 1000 wavenumber, cm - relative abundance Ihrelinnum minuman m 0 10 20 30 40 inumanninum 50 60 70 80 90 100 110 120 130 140 m/z

Answer 1

Proposed Structure Name: 3-chlorobut-1-ene Chemical Formula: C4H7C1 Exact Mass: 90.0236 34 Degree of Unsaturation = C+1 -- + FTIR Stretch (cm-1) 3090 2985 1660 1370 850 Bond C-H stretching (alkene) C-H stretching (Aliphatic) C=C stretch C-H rock C-Cl stretching

1H NMR IH Signal Integration No of protons Multiplicity Chemical Shift (ppm) 5.2 H marked 1 H marked 2 H marked 3 H marked 4 120072 6667 768 19554 3 1 1 2 doublets multiplet quintet 5 2. 48 1.6 Mass Fragments: m/z: 55 m/z: 90, 92 m/z: 75, 77 Multiplicity Rule: The multiplicity of any peak depends on the number of neighboring protons. If a protons contain n number of neighboring protons then the splitting will be n+1. Suppose a proton contains 2 neighboring H then it will give a triplet (2+1). However sometimes the splitting changes due to germinal vicinal etc. coupling in certain cases. The double bond equivalent is 1. It contains one pi-bond. Multiplet peak at 6 and two doublets peak at 5.2 is characteristics for terminal alkene group. The presence of Chlorine is confirmed by the mass spectrum. Chlorine isotopes are present in almost 75% and 25% natural abundancey. So two peaks for the molecular ion peak at 90 (100% wrt peak at 92) and 92 (33% wrt peak at 90) is appearing in mass spectrum. The presence of CH3 group is confirmed by the doublet peak at 1.6 ppm for 3H. The FTIR also corroborates the structure. Peak at 3090 cm is for alkene C-H stretching. Presence of chlorine shows C- Cl stretching peak at 850 cm.