Structure determination of organic compounds: by IR, UV-Vis, 1H & 13C NMR and Mass spectroscopic techniques.
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1.Among the following, the compound that displays an IR band at 2150 cm-1 is….
Azidobenzene is show IR bond at 2150 cm-1, str(NNN) v bond gives characteristic 2150 cm-1 bond.
2.In the 1H NMR spectrum of myrtenal, the two methyl groups are expected to display signals at (chemical shift values (δ)in ppm)
In the myrtenal, two methyl groups give two 1H-NMR peaks, because both methyl groups have different environment
Hb :1.33 (s,3H)
Ha :0.74 (s,3H)
3. In the UV-visible absorption spectrum of an α,β-unsaturated carbonyl compound, with increasing solvent polarity,
- n->π* transitions undergo hypsochromic shift, π->π* undergo bathochromic shift.
- n->π* transitions undergo bathochromic shift, π->π* undergo hypsochromic shift.
- bothn->π* and π->π* transitions undergo bathochromic shift.
- both n->π*
In the UV-visible absorption spectrum of an α,β-unsaturated carbonyl compound with increasing solvent polarity, n->π* transitions undergoes hypsochromic shift and π->π* undergoes bathochromic shift.
4.The correct structure of the compound, which shows following 13C NMR DEPT-135 data is 13C NMR DEPT-135: negative peaks at δ30.2, 31.9, 61.8, 114.7 ppm; positive peak at 130.4 ppm
In 13C-NMR DEPT-135 spectra gives peaks of only those carbon atoms which have two or three protons attached to it, i.e. –CH2 and –CH3. The –CH2 peaks comes downword (i.e. (-)ve peaks) and – CH3 and –CH peaks comes upward i.e. (+) ve peaks. In given compound 13C-NMR DEPT-135 gives four negative peaks which indicates presence of 4, -CH2 grops.
5.A compound displays the following spectral data. The correct structure of the compound is
6.In the mass spectrum of 1, 2-dichloroeth-ane, approximate ratio of peaks at m/z values 98, 100, 102 will be
(1.) 3 : 1 : 1
(2.) 9 : 6 : 1
(3.) 1 : 1 : 2
(4.) 1 : 2 : 1
When chlorine is present, the M + 2 peak becomes very significant. The heavy isotope these elements is two mass units heavier than the lighter isotope. The natural abundance of 37Cl is 32.5% that of 35Cl. When Chlorine is present, the M + 2 peak becomes quite intense. If a compound contains two chlorine atoms, a distinct M + 4 peak, as well as an intense M + 2 peak, should be observed.
The M : M+2 : M+4 peaks for two chlorine atom is in the ratio of 100 : 65.3 : 10.6 which on simplification gives 9 : 6 : 1